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Chapter 19

Binary Input & Output Java I ITP 120



ITP 120 Java Programming I2

Patrick Healy

Class #15 – Input and OutputChapter Objectives

To understand how I/O is handled in Java

To distinguish between text I/O and binary I/O

To read and write bytes using FileInputStream and FileOutputStream

To read and write primitive values and strings using the DataInputStream and

DataOutputStream classes

To store and restore objects using ObjectOutputStream and ObjectInputStream, and

to understand how objects are serialized and what kind of objects can be serialized

To use the Serializable interface to enable objects to be serializable (optional)

To know how to serialize arrays (optional)

To use RandomAccessFile for both read and write (Optional).




Patrick Healy

Class #15 – Input and Output

Overview

The java.io.* package provides a library of classes to read and writevarious types of data.

In Java, all data I/O is handled in the form of streams

Data streams can be byte streams or character streams

The java.io package has classes that process byte streams of all types

NOTE: In Java, a character is 2 BYTES !

Also NOTE: a Unicode character is 2 bytes !

The Reader and Writer classes process character streams.

Streams can be layered, so that one type of streams can be convertedto another type of streams by chaining. Chaining a character stream

reader to a byte stream reader to read bytes on one end and producecharacters at the other end .




Patrick Healy


Overview --- Streams

A stream is an abstraction of a continuous one-way flow of data.

Program

Output Stream

File

Input Stream


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Patrick Healy


2 Types of Stream Classes: Bytes & Characters

The stream classes can be categorized into two types: byte streams and

character streams.

The InputStream/OutputStream class is the

root of all BYTE stream classes

The Reader/Writer class is the root of all CHARACTER stream

classes.

The subclasses of InputStream/OutputStream are analogous to the

subclasses of Reader/Writer.



Patrick Healy


Byte Stream Classes (note: the word “stream” )

InputStream

OutputStream

RandomAccessFile

Object

PipeOutputStream

SequenceInputStream

StringBufferInputStream

ByteArrayOutputStream

ObjectOutputStream

FilterOutputStream

FileOutputStream

PipedInputStream

PushBackInputStream

BufferedInputStream

LineNumberInputStream

DataInputStream

BufferedOutputStream

DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

ByteArrayInputStream InputData

OutputData

ObjectOutput

ObjectInput



Patrick Healy

Class #15 – Input and OutputCharacter Stream Classes (Character = 2 bytes)

Reader

Writer

StreamTokenizer

Object

PrintWriter

BufferedWriter

CharArrayWriter

PipedWriter

FilterWriter

PipedReader

LineNumberReader

FileReader

PushBackReader

FileWriter

StringWriter

StringReader

InputStreamReader

CharArrayReader

BufferedReader

FilterReader

OutputStreamWriter



How is I/O Handled in Java?A File object encapsulates the properties of a file or a path, but does not contain

the methods for reading/writing data from/to a file. In order to perform I/O, youneed to create objects using appropriate Java I/O classes.

Formatter output = new Formatter("temp.txt");

output.format("%s", "Java 101");

output.close();

Scanner input = new Scanner(new File("temp.txt"));

System.out.println(input.nextLine());

Program

Input object

created from an

input class

Output objectcreated from an

output class

Input stream

Output stream

File

File 01011…1001

11001…1011



Text Files vs. Binary Files Data stored in a text file are represented in human-readable form.

Data stored in a binary file are represented in binary form. You

cannot read binary files. Binary files are designed to be read byprograms. For example, the Java source programs are stored in textfiles and can be read by a text editor, but the Java classes are stored inbinary files and are read by the JVM. The advantage of binary files isthat they are more efficient to process than text files.

Although it is not technically precise and correct, you can imaginethat a text file consists of a sequence of characters and a binary fileconsists of a sequence of bits. For example, the decimal integer 199 isstored as the sequence of three characters: '1', '9', '9' in a text file andthe same integer is stored as a byte-type value C7 in a binary file,because decimal 199 equals to hex C7.



Binary I/O

Text I/O requires encoding and decoding. The JVM converts a Unicode

to a file specific encoding when writing a character and coverts a filespecific encoding to a Unicode when reading a character. Binary I/O

does not require conversions. When you write a byte to a file, the original

byte is copied into the file. When you read a byte from a file, the exact

byte in the file is returned.

Text I/O program

The Unicode of

the characterEncoding/

Decoding

Binary I/O program

A byte is read/written(b)

(a)

e.g.

"199"

The encoding of the characteris stored in the file

0x31

e.g.

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7

The same byte in the file



Binary I/O Classes

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream



java.io.InputStream

+read(): int

+read(b: byte[]): int

+read(b: byte[], off: int,

len: int): int

+available(): int

+close(): void

+skip(n: long): long

+markSupported(): boolean

+mark(readlimit: int): void

+reset(): void

Reads the next byte of data from the input stream. The value byte is returned as

an int value in the range 0 to 255. If no byte is available because the end of

the stream has been reached, the value – 1 is returned.

Reads up to b.length bytes into array b from the input stream and returns the

actual number of bytes read. Returns -1 at the end of the stream.

Reads bytes from the input stream and stores into b[off], b[off+1], …,

b[off+len-1]. The actual number of bytes read is returned. Returns -1 at theend of the stream.

Returns the number of bytes that can be read from the input stream.

Closes this input stream and releases any system resources associated with the

stream.

Skips over and discards n bytes of data from this input stream. The actualnumber of bytes skipped is returned.

Tests if this input stream supports the mark and reset methods.

Marks the current position in this input stream.

Repositions this stream to the position at the time the mark method was last

called on this input stream.

The value returned is a byte as an

int type.

InputStream



The value is a byte as an int type.

OutputStream

java.io.OutputStream

+write(int b): void

+write(b: byte[]): void

+write(b: byte[], off: int,

len: int): void

+close(): void

+flush(): void

Writes the specified byte to this output stream. The parameter b is an int value.(byte)b is written to the output stream.

Writes all the bytes in array b to the output stream.

Writes b[off], b[off+1], …, b[off+len-1] into the output stream.

Closes this input stream and releases any system resources associated with thestream.

Flushes this output stream and forces any buffered output bytes to be written out.



FileInputStream/FileOutputStream

FileInputStream/FileOutputStream

associates a binary input/outputstream with an external file. All themethods inFileInputStream/FileOuptputStrea

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream



FileInputStream

To construct a FileInputStream, use the following constructors:

public FileInputStream(String filename)

public FileInputStream(File file)

A java.io.FileNotFoundException would occur if you attemptto create a FileInputStream with a nonexistent file.



FileOutputStream

To construct a FileOutputStream, use the following

constructors:

public FileOutputStream(String filename)

public FileOutputStream(File file)

public FileOutputStream(String filename, boolean append)

public FileOutputStream(File file, boolean append)

If the file does not exist, a new file would be created. If the filealready exists, the first two constructors would delete the currentcontents in the file. To retain the current content and append newdata into the file, use the last two constructors by passing true tothe append parameter.

TestFileStream

Run

http://html/TestFileStream.html

http://html/TestFileStream.html



FilterInputStream/FilterOutputStream

Filter streams are streams that filter bytes for some purpose. The basic byte input streamprovides a read method that can only be used for reading bytes. If you want to read integers,

doubles, or strings, you need a filter class to wrap the byte input stream. Using a filter classenables you to read integers, doubles, and strings instead of bytes and characters.FilterInputStream and FilterOutputStream are the base classes for filtering data. When youneed to process primitive numeric types, use DatInputStream and DataOutputStream to filterbytes.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream



DataInputStream/DataOutputStream DataInputStream reads bytes from the stream andconverts them into appropriate primitive type valuesor strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

DataOutputStream converts primitive type values or

strings into bytes and output the bytes to the stream.



DataInputStream

DataInputStream extends FilterInputStream and

implements the DataInput interface.

java.io.DataInput

+readBoolean(): boolean

+readByte(): byte

+readChar(): char

+readFloat(): float

+readDouble(): float

+readInt(): int

+readLong(): long

+readShort(): short +readLine(): String

+readUTF(): String

Reads a Boolean from the input stream.

Reads a byte from the input stream.

Reads a character from the input stream.

Reads a float from the input stream.

Reads a double from the input stream.

Reads an int from the input stream.

Reads a long from the input stream.

Reads a short from the input stream.Reads a line of characters from input.

Reads a string in UTF format.

InputStream

FilterInputStream

DataInputStream

+DataInputStream(

in: InputStream)



DataOutputStream DataOutputStream extends FilterOutputStream and implements the

DataOutput interface.

java.io.DataOutput

+writeBoolean(b: Boolean): void

+writeByte(v: int): void

+writeBytes(s: String): void

+writeChar(c: char): void

+writeChars(s: String): void

+writeFloat(v: float): void

+writeDouble(v: float): void

+writeInt(v: int): void

+writeLong(v: long): void +writeShort(v: short): void

+writeUTF(s: String): void

Writes a Boolean to the output stream.

Writes to the output stream the eight low-order bitsof the argument v.

Writes the lower byte of the characters in a string tothe output stream.

Writes a character (composed of two bytes) to theoutput stream.

Writes every character in the string s, to the output

stream, in order, two bytes per character.

Writes a float value to the output stream.

Writes a double value to the output stream.

Writes an int value to the output stream.

Writes a long value to the output stream.Writes a short value to the output stream.

Writes two bytes of length information to the outputstream, followed by the UTF representation of every character in the string s.

OutputStream

FilterOutputStream

DataOutputStream

+DataOutputStream(out: OutputStream)



Characters and Strings in Binary I/O

A Unicode consists of two bytes. The writeChar(char c)

method writes the Unicode of character c to the output.The writeChars(String s) method writes the Unicode foreach character in the string s to the output. Why UTF-8? What is UTF-8?

UTF-8 is a coding scheme that allows systems to operate with both ASCIIand Unicode efficiently. Most operating systems use ASCII. Java usesUnicode. The ASCII character set is a subset of the Unicode character set.Since most applications need only the ASCII character set, it is a waste torepresent an 8-bit ASCII character as a 16-bit Unicode character. The UTF-

8 is an alternative scheme that stores a character using 1, 2, or 3 bytes.ASCII values (less than 0x7F) are coded in one byte. Unicode values lessthan 0x7FF are coded in two bytes. Other Unicode values are coded inthree bytes.



Using DataInputStream/DataOutputStream

Data streams are used as wrappers on existing input and

output streams to filter data in the original stream. Theyare created using the following constructors:

public DataInputStream(InputStream instream)

public DataOutputStream(OutputStream outstream)

The statements given below create data streams. The firststatement creates an input stream for file in.dat; thesecond statement creates an output stream for file

out.dat.DataInputStream infile =

new DataInputStream(new FileInputStream("in.dat"));

DataOutputStream outfile =

new DataOut utStream new FileOut utStream "out.dat"

TestDataStream Run

http://html/TestDataStream.html





Checking End of File

TIP: If you keep reading data at the end of a stream, anEOFException would occur. So how do you check the

end of a file? You can use input.available() to check it.input.available() == 0 indicates that it is the end of a file.

Order and Format

CAUTION: You have to read the data in the same order and same format inwhich they are stored. For example, since names are written in UTF-8 usingwriteUTF, you must read names using readUTF.



BufferedInputStream/

BufferedOutputStream Using buffers to speed up I/O

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

BufferedInputStream/BufferedOutputStream does not contain new methods. All

the methods BufferedInputStream/BufferedOutputStream are inherited from theInputStream/OutputStream classes.

Constructing



Constructing

BufferedInputStream/BufferedOutputStream

// Create a BufferedInputStreampublic BufferedInputStream(InputStream in)

public BufferedInputStream(InputStream in, int bufferSize)

// Create a BufferedOutputStream

public BufferedOutputStream(OutputStream out)

public BufferedOutputStream(OutputStreamr out, int

bufferSize)



Case Studies: Copy File

This case study develops a program that copies files. The user

needs to provide a source file and a target file as command-linearguments using the following command:

java Copy source target

The program copies a source file to a target file and displays thenumber of bytes in the file. If the source does not exist, tell theuser the file is not found. If the target file already exists, tell theuser the file already exists. Copy Run

Obj t I/O

Optional

http://html/Copy.html

http://html/Copy.html



Object I/O

DataInputStream/DataOutputStream enables you to perform I/O for

primitive type values and strings. ObjectInputStream/ObjectOutputStreamenables you to perform I/O for objects in addition for primitive typevalues and strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

p

Obj tI tSt



ObjectInputStream

ObjectInputStream extends InputStream and implementsObjectInput and ObjectStreamConstants.

java.io.ObjectInput

+readObject(): Object Reads an object.

java.io.InputStream

java.io.ObjectInputStream

+ObjectInputStream(in: InputStream)

java.io.DataInput

ObjectStreamConstants

Obj tO t tSt



ObjectOutputStream

ObjectOutputStream extends OutputStream and implementsObjectOutput and ObjectStreamConstants.

java.io.ObjectOutput

+writeObject(o: Object): void Writes an object.

ava.io.OutputStream

java.io.ObjectOutputStream

+ObjectOutputStream(out: OutputStream)

java.io.DataOutput


U i Obj t St



Using Object Streams

You may wrap an

ObjectInputStream/ObjectOutputStream on anyInputStream/OutputStream using the following

constructors:

// Create an ObjectInputStream

public ObjectInputStream(InputStream in)

// Create an ObjectOutputStream

public ObjectOutputStream(OutputStream out)

TestObjectOutputStream Run

TestObjectInputStream Run

Random Access Files

http://html/TestObjectOutputStream.html

http://html/TestObjectInputStream.html

http://html/TestObjectInputStream.html

http://html/TestObjectOutputStream.html



Random Access Files

All of the streams you have used so far are known as read-

only or write-only streams. The external files of these streamsare sequential files that cannot be updated without creating anew file. It is often necessary to modify files or to insert newrecords into files. Java provides the RandomAccessFile classto allow a file to be read from and write to at randomlocations.

RandomAccessFile



RandomAccessFile

Creates a RandomAccessFile stream with the specified File object andmode.

Creates a RandomAccessFile stream with the specified file name

string and mode.

Closes the stream and releases the resource associated with the stream.

Returns the offset, in bytes, from the beginning of the file to where the

next read or write occurs.

Returns the length of this file.

Reads a byte of data from this file and returns – 1 an the end of stream.

Reads up to b.length bytes of data from this file into an array of bytes.

Reads up to len bytes of data from this file into an array of bytes.

Sets the offset (in bytes specified in pos) from the beginning of the

stream to where the next read or write occurs.

Sets a new length of this file.

Skips over n bytes of input discarding the skipped bytes.

Writes b.length bytes from the specified byte array to this file, startingat the current file pointer.

Writes len bytes from the specified byte array starting at offset off to

this file.

DataInput DataInput

java.io.RandomAccessFile

+RandomAccessFile(file: File, mode:

String)

+RandomAccessFile(name: String,

mode: String)

+close(): void

+getFilePointer(): long

+length(): long

+read(): int


+read(b: byte[], off: int, len: int) : int

+seek(long pos): void

+setLength(newLength: long): void

+skipBytes(int n): int

+write(b: byte[]): void

+write(byte b[], int off, int len) +write(b: byte[], off: int, len: int):

void

Fil P i



File Pointer

A random access file consists of a sequence of bytes.

There is a special marker called file pointer that ispositioned at one of these bytes. A read or writeoperation takes place at the location of the file pointer.When a file is opened, the file pointer sets at the

beginning of the file. When you read or write data to thefile, the file pointer moves forward to the next data. Forexample, if you read an int value using readInt(), theJVM reads four bytes from the file pointer and now the

file pointer is four bytes ahead of the previous location.

bytefile byte … byte byte byte byte byte … byte byte byte byte byte

file pointer


file pointer

(A) Before readInt()

(B) Before readInt()

i M h d



RandomAccessFile Methods

Many methods in RandomAccessFile are the same as those

in DataInputStream and DataOutputStream. Forexample, readInt(), readLong(), writeDouble(),readLine(), writeInt(), and writeLong() can be usedin data input stream or data output stream as well as inRandomAccessFile

streams.

M h d



RandomAccessFile Methods, cont.

void seek(long pos) throws

IOException;

Sets the offset from the beginning of the

RandomAccessFile stream to where the next read

or write occurs.

long getFilePointer()

IOException;

Returns the current offset, in bytes, from the

beginning of the file to where the next read

or write occurs.

i M h d




long length()IOException

Returns the length of the file.

final void writeChar(int v)

throws IOException

Writes a character to the file as a two-byte Unicode, with

the high byte written first.

final void writeChars(String s)

throws IOException Writes a strin to the file as a se uence of

R d A Fil C t t



RandomAccessFile Constructor

RandomAccessFile raf =

new RandomAccessFile("test.dat", "rw");//allows read and write

RandomAccessFile raf =

new RandomAccessFile("test.dat", "r");//read only

Case Studies: Address BookOptional



Case Studies: Address Book

Now let us use RandomAccessFile to create a useful project for

storing and viewing and address book. The user interface of theprogram is shown in Figure 16.24. The Add button stores a new

address to the end of the file. The First , Next , Previous, and

Last buttons retrieve the first, next, previous, and last addresses

from the file, respectively.

Fixed Length String I/O



Fixed Length String I/O

Random access files are often used to process files of

records. For convenience, fixed-length records areused in random access files so that a record can belocated easily. A record consists of a fixed number of fields. A field can be a string or a primitive data type.

A string in a fixed-length record has a maximum size.If a string is smaller than the maximum size, the rest of the string is padded with blanks.

Record 1 Record 2 Record n

Field1 Field 2 … Field k

file

e.g.,

Student 1 Student 2 Student n

name street city state zip

FixedLengthStringIO

http://html/FixedLengthStringIO.html

http://html/FixedLengthStringIO.html



End of Presentation

Binary Input & Output Chapter 18


C Fil j




Patrick Healy

CopyFile.java

CopyFile.java is a program that copies files. The user needs to provide a sourcefile and a target file as command-line arguments using the following command:

java CopyFile source target

Also: java CompFile source target

The program copies a source file to a target file and displays the number of bytes

in the file. If the source does not exist, tell the user the file is not found. If the targetfile already exists, tell the user the file already exists.


Object I/O (optional)




Patrick Healy

Object I/O (optional)

DataInputStream/DataOutputStream enables you to perform I/O for primitive type values andstrings. ObjectInputStream/ObjectOutputStream enables you to perform I/O for objects in

addition for primitive type values and strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream





Patrick Healy

ObjectInputStream (optional)

ObjectInputStream extends InputStream and implements ObjectInput and

ObjectStreamConstants.

java.io.ObjectInput

+readObject(): Object Reads an object.

java.io.InputStream

java.io.ObjectInputStream

+ObjectInputStream(in: InputStream)

java.io.DataInput






Patrick Healy

ObjectOutputStream (optional)

ObjectOutputStream extends OutputStream and implements ObjectOutput and

ObjectStreamConstants.

java.io.ObjectOutput

+writeObject(o: Object): void Writes an object.

ava.io.OutputStream

java.io.ObjectOutputStream

+ObjectOutputStream(out: OutputStream)

java.io.DataOutput



Using Object Streams (optional)




Patrick Healy

Using Object Streams (optional)

You may wrap an ObjectInputStream/ObjectOutputStream on anyInputStream/OutputStream using the following constructors:

// Create an ObjectInputStream

public ObjectInputStream(InputStream in)

// Create an ObjectOutputStream

public ObjectOutputStream(OutputStream out)

Demo: TestObjectOutputStream.java

TestObjectInputStream.java


The Serializable Interface




Patrick Healy

The Serializable Interface

Not all objects can be written to an output stream. Objects that CAN be written to an object

stream is said to be serializable. A serializable object is an instance of the java.io.Serializable

interface. So the class of a serializable object must implement the Serializable interface.The Serializable interface is a marker interface. It has no methods, so you don't need to add

additional code in your class that implements Serializable.

Implementing this interface enables the Java serialization mechanism to automate the process

of storing the objects and arrays.





Patrick Healy

The transient Keyword

If an object is an instance of Serializable, but it contains non-serializable instance data fields,

can the object be serialized? The answer is NO !

To enable the object to be serialized, you can use the transient keyword to mark these data

fields to tell the JVM to ignore these fields when writing the object to an object stream.

Class #15 – Input and OutputThe transient Keyword, cont.




Patrick Healy

Consider the following class:

public class ITP120 implements java.io.Serializable {

private int v1;

private static double v2;

private transient A v3 = new A();

}

class A { } // A is not serializable

When an object of the ITP120 class is serialized, only variable v1 isserialized. Variable v2 is not serialized because it is a static variable, andvariable v3 is not serialized because it is marked transient. If v3 were notmarked transient, a java.io.NotSerializableException would occur.


Serializing Arrays (optional)




Patrick Healy

Serializing Arrays (optional)

An array is serializable if all its elements are serializable. So an entire array can be saved

using writeObject into a file and later restored using readObject.

Listing 18.6 stores an array of five int values, an array of three strings, and an array of two

JButton objects, and reads them back to display on the console.

Demo Program: TestObjectStreamForArray.java


Random Access Files




Patrick Healy

Random Access Files

All of the streams you have used so far are known as read-only or write-only streams. The

external files of these streams are sequential files that cannot be updated without creating

a new file.

It is often necessary to modify files or to insert new records into files. Java provides the

RandomAccessFile class to allow a file to be read from and write to at random locations.

Class #15 – Input and OutputRandomAccessFile




Patrick Healy

Creates a RandomAccessFile stream with the specified File object andmode.

Creates a RandomAccessFile stream with the specified file name

string and mode.

Closes the stream and releases the resource associated with the stream.



Returns the length of this file.Reads a byte of data from this file and returns – 1 an the end of stream.

Reads up to b.length bytes of data from this file into an array of bytes.

Reads up to len bytes of data from this file into an array of bytes.

Sets the offset (in bytes specified in pos) from the beginning of the

stream to where the next read or write occurs.

Sets a new length of this file.

Skips over n bytes of input discarding the skipped bytes.Writes b.length bytes from the specified byte array to this file, starting

at the current file pointer.

Writes len bytes from the specified byte array starting at offset off to

this file.

DataInput DataInput

java.io.RandomAccessFile

+RandomAccessFile(file: File, mode:String)

+RandomAccessFile(name: String,

mode: String)

+close(): void

+getFilePointer(): long

+length(): long+read(): int


+read(b: byte[], off: int, len: int) : int

+seek(long pos): void

+setLength(newLength: long): void

+skipBytes(int n): int+write(b: byte[]): void

+write(byte b[], int off, int len) +write(b: byte[], off: int, len: int):

void

Class #15 – Input and OutputFile Pointers




Patrick Healy

A random access file consists of a sequence of bytes. There is a specialmarker called file pointer that is positioned at one of these bytes. A read or

write operation takes place at the location of the file pointer. When a file isopened, the file pointer sets at the beginning of the file. When you read or write data to the file, the file pointer moves forward to the next data. For example, if you read an int value using readInt(), the JVM reads four bytes from the file pointer and now the file pointer is four bytes ahead of the

previous location.

Class #15 – Input and OutputFile Pointers

( i th i t 4 b t h d)




Patrick Healy

(moving the pointer 4 bytes ahead)


file pointer


file pointer

(A) Before readInt()

(B) Before readInt()


R d A Fil Methods




Patrick Healy

RandomAccessFile Methods

Many methods in RandomAccessFile are the same as those in

DataInputStream and DataOutputStream .

For example, readInt(), readLong(), writeDouble(), readLine(), writeInt(), and writeLong()

can be used in data input stream or data output stream as well as inRandomAccessFile streams.

Class #15 – Input and OutputRandomAccessFile Methods, cont.




Patrick Healy

void seek(long pos) throws IOException;

Sets the offset from the beginning of the RandomAccessFile stream to

where the next read or write occurs.

long getFilePointer() IOException;

Returns the current offset, in bytes, from the

beginning of the file to where the next read or write occurs.


RandomAccessFile Methods cont




Patrick Healy


long length()IOException

Returns the length of the file.

final void writeChar(int v) throwsIOException

Writes a character to the file as a two-byte Unicode, with the high byte written

first.

final void writeChars(String s)throws IOException

Writes a string to the file as a sequence of characters.


RandomAccessFile Constructors




Patrick Healy

RandomAccessFile Constructors

RandomAccessFile raf =new RandomAccessFile("test.dat", "rw"); //allows read and write to the file

RandomAccessFile raf =new RandomAccessFile("test.dat", "r"); //read only

Demo program: TestRandomAccessFile.java

(uses FixedLengthStringIO.java)

Case Study: Address Book



Now let us use RandomAccessFile to create a useful project for

storing and viewing and address book. The user interface of theprogram is shown in Figure 16.24. The Add button stores a new

address to the end of the file. The First , Next , Previous, and

Last buttons retrieve the first, next, previous, and last addresses

from the file, respectively.Run: AddressBook.java which uses FixedLengthStringIO.java

Chapter 18 Demo Programs



59


ReadBytes.java (skip) WriteData.javaWriteDemo.java ReadData.java

ShowFile.java

CopyFile.java CopyFileUsingByteStream.java

CompFile.java

RWData.java

RandomAccessDemo.java

PrintWriterDemo.javaReadChars.java or BuffReader.java

ReadLines.java (BufferedReader)




60


TextFileScannerDemo.java Uses input file morestuff.txt

HasNextLineDemo.java

Uses input file original.txt

and creates output file numbered.txt

BufferReaderDemo.java

Uses input file: buffer.txt




61


TestDataStreams.javaTestFileClass.java

TestPrintWriters.java

ViewFile.java (GUI text file viewer program)

needs MyFrameWithExitHanding.java class fileParsingTextFile.java (needs grades.dat file)

(creates gradesout.dat)

TestRandomAccessFile.java

AddressBook.java (creates file address.dat) needs FixedLengthStringIO.class file




62


TestDataStream.javaTestFileReader.java (needs temp.txt)

TestFileStream.java

TestFileWriter.java (needs testdata.txt)

TestObjectStreamForArray.java ( creates array.dat)TestObjectOutputStream.java

(creates object.dat)

TestObjectInputStream.java (reads object.dat)

Class #15 – Input and OutputChapter 18 Input / Output




Patrick Healy

Optional: More on Java File I/O

Chapter 18 Java I ITP 120

Class #15 – Input and OutputChapter 18: More on Input and Output

Stream Classes (byte & character streams)




Patrick Healy

Stream Classes (byte & character streams) Predefined Streams (System.in, System.out, System.err)

Processing External FilesData Streams

Print Streams

Buffered Streams

Text Input and Output on the Console

Random Access Files

Class #15 – Input and OutputChapter 18 Input /Output Objectives

Understand input & output streams and learn how to create them




Patrick Healy

Understand input & output streams and learn how to create them.

Discover the uses of byte and character streams.

To know how to read from / write to external files using file streams.

To become familiar with the File class.

To use print streams to output data of primitive types in text format.

To know how to read and write text data files.

Use text input and output on the console.

Use RandomAccessFile for reading & writing random access files.

Class #15 – Input and OutputOverview

The java io * package provides a library of classes to read and write




Patrick Healy

The java.io. package provides a library of classes to read and writevarious types of data.

In Java, all data I/O is handled in the form of streams Data streams can be byte streams or character streams

The java.io package has classes that process byte streams of all types

NOTE: In Java, a character is 2 BYTES !

NOTE: Unicode character is 2 bytes ! The Reader and Writer classes process character streams.

Streams can be layered, so that one type of streams can be convertedto another type of streams by chaining. Chaining a character streamreader to a byte stream reader to read bytes on one end and produce

characters at the other end .

Class #15 – Input and OutputOverview Streams

In Java all Input/Output is handled by streams




Patrick Healy

In Java, all Input/Output is handled by streams

A stream is an abstraction of the continuous one-way flow of data

Java streams can be applied to any source of data, so it is easy to getinput from the keyboard and send output to a monitor, and the same

applies to file input & output.

All streams EXCEPT random-access file streams flow only in one

direction.

See the diagram on the next slide

Class #15 – Input and OutputOverview --- Streams




Patrick Healy

A stream is an abstraction of a continuous one-way flow of data.

Program

Output Stream

File

Input Stream

Class #15 – Input and OutputOverview and Background

The original version of Java defined only the byte stream but character




Patrick Healy

The original version of Java defined only the byte stream, but character

streams were quickly added.

Byte streams can be used when reading or writing binary data. Character streams are designed for handling character I/O.

Character streams use UNICODE. In Java, a character is 2 bytes

Unicode is for the internationalization of Java in different languages.

The Java I/O system is quite LARGE because of the TWO separateclass hierarchies of bytes and streams.

How is I/O Handled in Java?



A File object encapsulates the properties of a file or a path, but does not contain

the methods for reading/writing data from/to a file. In order to perform I/O, you

need to create objects using appropriate Java I/O classes.

Formatter output = new Formatter("temp.txt");output.format("%s", "Java ITP 120");

output.close();

Scanner input = new Scanner(new File("temp.txt"));

System.out.println(input.nextLine());

Program

Input object

created from an

input class

Output object

created from an

output class

Input stream

Output stream

File

File 01011…1001

11001…1011

Class #15 – Input and OutputText Files vs. Binary Files




Patrick Healy

Data stored in a text file are represented in human-readable form. Datastored in a binary file are represented in binary form. You cannot read

binary files. Binary files are designed to be read by programs. For example,the Java source programs are stored in text files and can be read by a texteditor, but the Java classes are stored in binary files and are read by theJVM.

The advantage of binary files is that they are more efficient to process than

text files.

Although it is not technically precise and correct, you can imagine that atext file consists of a sequence of characters and a binary file consists of asequence of bits. For example, the decimal integer 199 is stored as thesequence of three characters: '1', '9', '9' in a text file and the same integer isstored as a byte-type value C7 in a binary file, because decimal 199 equalsto hex C7 ( 12 x 16 + 7 = 192 + 7 = 199 decimal )

Binary I/O

T I/O i di d d di Th JVM U i d



Text I/O requires encoding and decoding. The JVM converts a Unicode

character to file-specific encoding when writing a character, and coverts

a file-specific encoding to a Unicode character when reading a character.Binary I/O does not require conversions. When you write a byte to a file,

the original byte is copied into the file. When you read a byte from a file,

the exact byte in the file is returned.

Text I/O program

The Unicode of

the characterEncoding/

Decoding

Binary I/O program

A byte is read/written(b)

(a)

e.g.

"199"

The encoding of the character

is stored in the file

0x31

e.g.

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7

The same byte in the file

Class #15 – Input and Output2 Types of Stream Classes: Bytes & Characters




Patrick Healy

The stream classes can be categorized into two types: byte streams and

character streams. The InputStream/OutputStream class is the

root of all byte stream classes

The Reader/Writer class is the root of all character stream

classes.

The subclasses of InputStream/OutputStream are analogous to the

subclasses of Reader/Writer.

Class #15 – Input and OutputByte Stream Classes (note: “stream” )

D t I tStByteArrayInputStream

I tD t




Patrick Healy

InputStream

OutputStream

RandomAccessFile

Object

PipeOutputStream

SequenceInputStream

StringBufferInputStream

ByteArrayOutputStream

ObjectOutputStream

FilterOutputStream

FileOutputStream

PipedInputStream

PushBackInputStream

BufferedInputStream

LineNumberInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

InputData

OutputData

ObjectOutput

ObjectInput

Class #15 – Input and OutputCharacter Stream Classes (Character = 2 bytes)

CharArrayReader




Patrick Healy

Reader

Writer

StreamTokenizer

Object

PrintWriter

BufferedWriter

CharArrayWriter

PipedWriter

FilterWriter

PipedReader

LineNumberReader

FileReader

PushBackReader

FileWriter

StringWriter

StringReader

InputStreamReader

BufferedReader

FilterReader

OutputStreamWriter

Class #15 – Input and OutputPredefined Streams in Java

All Java programs automatically import the java.lang package.




Patrick Healy

p g y p j g p g

The java.lang package defines a class called System whichencapsulates several aspects of the runtime environment.

The System class contains 3 predefined stream variables called:

in, out, and err (System.in, System.out, System.err)

These variables are declared as public and static with the System

class. This means they can be used by any other part of your program

and without a reference to a specific object in the System class.

Class #15 – Input and OutputPredefined Streams in Java: System class

System.in refers to the standard input stream which is the




Patrick Healy

keyboard by default. (Keyboard )

System.out refers to the standard output stream which is the

console by default. (Monitor)

System.err refers to the standard error stream which is also theconsole by default. (Monitor)

These streams may be redirected to any compatible I/O device.

Class #15 – Input and OutputPredefined Streams in Java: System class

System.in is an object of type InputStream. (byte stream)




Patrick Healy

System.out is an object of type PrintStream. (byte stream)

System.err is an object of type PrintStream. (byte stream)

They are all byte streams and are a part of the original Java

specification.

They are NOT character streams ! (Unicode character = 2 bytes)

Class #15 – Input and OutputReading Keyboard Input

// Read an array of bytes from the keyboard.

i j i *




Patrick Healy

import java.io.*;

public class ReadBytes {

public static void main(String[ ] args)

throws IOException {

byte data[ ] = new byte[10]; // Byte array “data” holds 10 bytes

System.out.println("Enter some characters:");

System.in.read(data); // Use the “read” method to read some bytes

System.out.print("You entered: ");

for(int i=0; i < data.length; i++)

System.out.print((char) data[i]); // Cast data to a character

} // End main method} // End class ReadBytes

Class #15 – Input and OutputReading Keyboard Input

Here is a sample run from the previous program:




Patrick Healy

Enter some characters: (prompt from program)READ BYTES (User entered READ BYTES)

You entered: READ BYTES (output from program)

Class #15 – Input and OutputWriting Output to the Monitor

// Demonstrate System.out.write(). Java program WriteDemo.java




Patrick Healy

public class WriteDemo

{public static void main(String[ ] args)

{

int b; // Program prints an „X‟ on the monitor

b = 'X'; // The character is an intSystem.out.write(b); // A byte stream; write low-order 8 bits

System.out.write('\n'); // Print a newline character \n

} // End of main( ) // print() and println() are easier to use than write()

} // End of class WriteDemo

Class #15 – Input and OutputStream classes (Bytes & Characters)

The java.io package provides two categories of classes:B te stream readers and riters




Patrick Healy

Byte stream readers and writers Character stream readers and writers

At the top of the hierarchy for stream classes are the abstract classesInputStream and Output Stream

The subclasses branch out and specializes into the different types of streams that they handle.

InputData, OutputData, and ObjectInput interfaces are implemented bythe classes that handle data, such as, int, double, char, etc., andobjects. Only ObjectInput specifies methods for reading objects.

DataInputStream - which is a subclass of FilterInputStream, which inturn is a subclass of InputStream – implements the InputData interface

and can read primitive data, and objects from byte streams.

Class #15 – Input and OutputStream Classes

FileInputStream can read raw streams of data from files.




Patrick Healy

DataOutputStream can write primitive data; this class implements the

OutputData interface RandomAccessFile implements both InputData and OutputData

interfaces, therefore, it can read and write data to streams.

ObjectOutputStream implements the ObjectOutput interface and can

write object data to streams.

Class #15 – Input and OutputInputStream Class (for reading bytes)




Patrick Healy

The following methods are defined in InputStream

and are often useful: public abstract int read() throws IOException

Reads the next byte and returns its value in therange of 0 to 255. At the end of the stream, itreturns a - 1.

public int read(byte b[]) throws IOException

Reads bytes into array b,, returns b.length if thenumber of available bytes is >= b.length. Returnsthe number of bytes read if the number of available

bytes is < than b.length, and returns –1 at the end

of the stream.





Patrick Healy

The following methods are defined in InputStream and are often useful:

public void close() throws IOException

This method closes the input stream.

public void available() throws IOExceptionReturns the number of bytes that can be read from the input stream without blocking.





Patrick Healy

The following method is defined in InputStream and isoften useful:

public long skip(long n) throws IOException

Skip over and discard n bytes of data from theinput stream. The actual number of bytes skipped

is returned.

Class #15 – Input and OutputReading & Writing Files Using Byte Streams

To create a byte stream linked to a file, use FileInputStream or

FileOutputStream




Patrick Healy

FileOutputStream

To open a file, create an object of one of these classes, specifying thename of the file as an argument to the constructor.

Once the file is open, you can read from the file or write to the file.

To read form a file, you may use the read( ) method.

int read( ) throws IOException When you are done with a file, you should close it by calling close()

void close( ) throws IOException

Closing a file releases the system resources allocated to the file,

allowing them to be used by another file.


/* Display a text file.

T hi if h




Patrick Healy

To use this program, specify the name

of the file that you want to see.For example, to see a file called TEST.TXT,

use the following command line.

Command line usage: java ShowFile TEST.TXT */

// Program ShowFile.java follows on the next slide ->


public class ShowFile {





Patrick Healy

( g g )


int i;FileInputStream fin; // Declare file pointer

try {

fin = new FileInputStream(args[0]); } // Open the input file

catch(FileNotFoundException exc) {

System.out.println(“Error: “ + exc.getMessage( ));

System.out.println("File Not Found");

return; }

} catch(ArrayIndexOutOfBoundsException exc) {


System.out.println("Usage is: java ShowFile File.txt ");

return; }


// Read bytes until EOF is encountered

d {




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do {

i = fin.read( ); // Read an integer if(i != -1) System.out.print((char) i); // Cast the int as a char

} while( i != -1); // When i = -1, EOF is encountered

fin.close( ); // Close the input file

} // End of main method

} // End of class ShowFile

Class #15 – Input and OutputWriting to a File Using Byte Streams

/* Java program to Copy a text file.

T thi if th




Patrick Healy

To use this program, specify the name

of the source file and the destination file.For example, to copy a file called File1.txt

to a file called File2.txt , use the following

on the command line:

Usage: java CopyFile File1.txt File2.txt */


// CopyFile.java Demo byte stream file operations

import java io *;




Patrick Healy

import java.io.*;

public class CopyFile {public static void main(String[ ] args) throws IOException

{

int i;

FileInputStream fin; // Declare 2 byte stream files (pointers)

FileOutputStream fout; // Output file pointer


try { // outer try block




Patrick Healy

try { // outer try block

// try to open input file

try { // inner try

fin = new FileInputStream(args[0]);

} catch(FileNotFoundException exc) {

System.out.println(“Error:”

+ exc.getMessage( ) );

System.out.println("Input File Not Found");return; }


// open output file

try {




Patrick Healy

try {

fout = new FileOutputStream(args[1]);} catch(FileNotFoundException exc) {

System.out.println(“Error: “ + exc.getMessage());

System.out.println("Error Opening Output File");

return;

}

} // End of outer try block


Writing to a File Using Byte Streams

catch(ArrayIndexOutOfBoundsException exc) {

System.out.println(“Error: “ + exc.getMessage( ) );




Patrick Healy

System.out.println("Usage: CopyFile File1 File2");

return; }try { // Try to copy file1 to file2

do {

i = fin.read( ); // Read a byte

if(i != -1) fout.write(i); // Write the byte to the output file

} while(i != -1); // Loop while not at EOF (-1)

} // End of try block

catch(IOException exc)

{ System.out.println("File Error"); }

fin.close( ); // Close the input file

fout.close( ); // Close the output file

} // End of main( ) method

} // End of class CopyFile


Reading & Writing Binary Data

So far, we have been reading and writing bytes containing ASCII bytes.

You may want to create a file that contains other types of data such as




Patrick Healy

You may want to create a file that contains other types of data such as

integers, doubles, or shorts , that is: int, double, short, etc.

In Java, to read and write binary values of the simple Java data types,

you should use:

DataInputStream and DataOutputStream (for binary data)

DataOutputStream implements the OutputData interface.

The OutputData interface defines methods that write all of Java‟s

simple data types to a file.



Note: Binary data is NOT in human-readable text format, obviously.




Patrick Healy

The constructor for DataOutputStream is:

DataOutputStream(OutputStream outputStream)

outputStream is the stream to which the binary data is written.



The constructor for DataInputStream is:

DataInputStream(InputStream inputStream)




Patrick Healy

DataInputStream(InputStream inputStream)

inputStream is the stream that is linked to the instance of

DataInputStream being created.

DataInputStream implements the DataInput interface which providesthe methods for reading all of Java‟s simple data types.

DataInputStream uses an InputStream instance as its foundation,

overlaying it with methods that read the various Java data types.


Reading & Writing Binary Data Examples

To create an input stream for the file in.dat ( bytes)




Patrick Healy

DataInputStream infile =new DataInputStream(new FileInputStream(“in.dat”));

To create an output stream for the file out.dat:

DataOutputStream outfile =

new DataOutputStream(new FileOutputStream(“out.dat”));



Common Input Methods Defined by DataInputStream (a byte stream)

Input Method Purpose




Patrick Healy

Input Method Purpose

boolean readBoolean ( ) Reads a booleanbyte readByte ( ) Reads a byte

char readChar ( ) Reads a char

double readDouble( ) Reads a double

float readFloat ( ) Reads a float

int readInt ( ) Reads an int

long readLong ( ) Reads a long

short readShort ( ) Reads a short



Common Output Methods Defined by DataOutputStream ( byte stream)

Output Method Purpose




Patrick Healy

p p

void writeBoolean (boolean val) writes the boolean specified by valvoid writeByte (int val) writes the low-order byte val

void writeChar(int val) writes the value val as a char

void writeDouble(double val) writes the double val

void writeFloat(float val) writes the float val

void writeInt(int val) writes the int val

void writeLong(long val) writes the long val

void writeShort(int val) writes val as a short



Here is a Java program that demonstrates DataOutputStream and

DataInputStream. It writes and then reads back various types of data




Patrick Healy

to and from a file.

// Write and then read back binary data.

import java.io.*;

public class RWData {

public static void main(String[ ] args) throws IOException{

DataOutputStream dataOut; // Declare output, input file pointers

DataInputStream dataIn;



int i = 120;

double d = 1049.56;




Patrick Healy

boolean b = true;

try {

dataOut = new

DataOutputStream(new FileOutputStream(“testdata")); }

catch(IOException exc) {


System.out.println("Cannot open file.");

return; }



try { // Write the binary data

System.out.println("Writing " + i);

dataOut writeInt(i);




Patrick Healy

dataOut.writeInt(i);

System.out.println("Writing " + d);

dataOut.writeDouble(d);

System.out.println("Writing " + b);

dataOut.writeBoolean(b);

System.out.println("Writing " + 12.2 * 7.4);

dataOut.writeDouble(12.2 * 7.4);

}




System.out.println("Write error: + exc.getMessage( )");

}




Patrick Healy

}

dataOut.close( );System.out.println(); // Print a blank line

// Now, read them back.

try {

dataIn = new

DataInputStream(new FileInputStream("testdata"));

}


System.out.println("Cannot open file. + exc.getMessage( )");

return;

}



try { // Read the binary data

i = dataIn.readInt();

S t t i tl ("R di " i)




Patrick Healy

System.out.println("Reading " + i);

d = dataIn.readDouble();

System.out.println("Reading " + d);

b = dataIn.readBoolean();System.out.println("Reading " + b);

d = dataIn.readDouble();

System.out.println("Reading " + d);

}




System.out.println("Read error.“ + exc.getMessage( ) ); }




Patrick Healy

dataIn.close();} // End of main ( )

} // End of class RWData

The output from the previous program follows:

Writing 120 Reading 120

Writing 1023.56 Reading 1049.56

Writing true Reading true

Writing 90.28 Reading 90.28


Reader class methods for reading characters

The Reader class is similar to the InputStream class. The




Patrick Healy

methods in Reader are subject to character interpretation.

Remember: A character is 2 bytes !

public abstract int read() throws IOException

public int read(char b[]) throws IOException


public void skip() throws IOException


OutputStream ( bytes) & Writer (for characters)

Like InputStream (for reading bytes) and Reader (for reading

h ) O S d W i h




Patrick Healy

characters), OutputStream and Writer are the counterparts.

They are the base classes for for all output streams of bytes and

characters, respectively.

The next slide shows methods which are in both OutputStream and

Writer.

See next slide ->


OutputStream (Writing bytes)

public abstract void write(int b) throws IOException

Write a byte b (for OutputStream) or a charcter




Patrick Healy

Write a byte b (for OutputStream) or a charcter

(for Writer) public void write(byte[] b) throws IOException

This method writes all bytes in the array b to theoutput stream (for OutputStream) or characters inthe array of characters (for Writer)


This method closes the output stream.

public void flush() throws IOException

Flush the output stream and send any buffered data

in the stream to its destination.


Writer (Writing characters) (Same as OutputStream)

public abstract void write(int b) throws IOException

Write a byte b (for OutputStream) or a character




Patrick Healy

Write a byte b (for OutputStream) or a character

(for Writer) public void write(byte[] b) throws IOException

This method writes all bytes in the array b to theoutput stream (for OutputStream) or characters inthe array of characters (for Writer)


This method closes the output stream.

public void flush() throws IOException

Flush the output stream and send any buffered data

in the stream to its destination.


Console Input using Character Streams

For Java code that will be internationalized, inputting data from the

console using Java‟s character -based streams is a better, more

convenient way to read characters from the keyboard than using byte




Patrick Healy

convenient way to read characters from the keyboard than using byte

streams.

Since System.in is a byte-stream, you need to wrap System.in inside of

some type of Reader.

The best class for reading console input is BufferedReader whichsupports a buffered input stream. (BufferedReader inherits from

Reader)

But, you cannot construct a BufferedReader directly from System.in



You must first convert the input from System.in from a byte stream

into a character stream. To do this, you must use InputStreamReader.

InputStreamReader converts bytes to characters




Patrick Healy

InputStreamReader converts bytes to characters.

To obtain an InputStreamReader object that is linked to System.in, use

the following constructor:

InputStreamReader ( InputStream inputStream )

Since System.in refers to an object of type InputStream, it can be used

for inputStream such as in: InputStreamReader(System.in)



Next, using the object produced by InputStreamReader, construct a

BufferedReader using the following constructor:




Patrick Healy

BufferedReader(Reader inputReader )

Here, inputReader is the stream that is linked to the instance of

BufferedReader being created.



Putting it all together, the following line of code creates a BufferReader

that is connected to the keyboard.




Patrick Healy

BufferedReader br =

new BufferedReader( new InputStreamReader(System.in));

After the above statement executes, “br” will be a character-based

stream that is linked to the console thru System.in (which reads bytes)



Reading Characters

Characters can be read from System.in using the read( ) method

defined by BufferedReader




Patrick Healy

defined by BufferedReader.

BufferedReader defines the following versions of read( )

int read( ) throws IOException

int read(char data[ ] ) throws IOException int read(char data[ ], int start, int max) throws IOException



int read( ) throws IOException

reads a single Unicode character and returns a -1 when the end of thestream is reached.




Patrick Healy

int read(char data[ ]) throws IOException

reads characters from the input stream until:

(1) the array is full, (2) EOF is reached, or (3) an error occurs.

int read(char data[ ], int start , int max ) throws IOException

reads input into array data beginning at the location specified bystart , storing up to max characters. It returns the number of charactersread or -1 when the end of the stream is reached.

Pressing the [Enter] key generates an end-of-stream condition.



The following program demonstrates the read( ) method by reading

characters from the console until the user types a period.




Patrick Healy

// Use a BufferedReader to read characters from the console.

import java.io.*;

public class ReadChars {

public static void main(String[ ] args) throws IOException{



BufferedReader br = new

BufferedReader(new InputStreamReader(System.in));

System out println("Enter some characters; period to quit ");




Patrick Healy

System.out.println("Enter some characters; period to quit.");

// read characters

do {

c = (char) br.read(); // Cast the character to a byte

System.out.println(c); // Print the character } while(c != '.'); // Loop as long as the input char is not a period


} // End of ReadChars class



Output from the previous program could be:

Enter some characters; period to quit.

I




Patrick Healy

I

T

P

J

A

V

A

. <- note the period character which stopped the input stream



Reading Character Strings from the Keyboard …

To read a string from the keyboard, use the version of readLine( ) that is

a member of the BufferedReader class. The general form is:




Patrick Healy

a member of the BufferedReader class. The general form is:

String readLine( ) throws IOException

It returns a string object that contains the characters read. It returnsnull if an attempt is made to read beyond the end of the stream.



The following program demonstrates BufferedReader and the readLine() method. The

program reads and displays lines of text until the user enters the word “stop”

// Read a string from console using a BufferedReader.




Patrick Healy

import java.io.*;class ReadLines {


throws IOException

{

// create a BufferedReader using System.in

BufferedReader br = new BufferedReader(new

InputStreamReader(System.in));

String str;




Console Output using Character Streams

The preferred method of writing to the console (monitor) when using

Java is through a PrintWriter stream.

PrintWriter is one of the character-based classes.




Patrick Healy

Using a character-based class makes it easier to internationalize

Java programs.

PrintWriter has several constructors, but this is the one to be used in

the demonstration program which is on the following slides:

PrintWriter(OutputStream outputStream, boolean flushOnNewline)



PrintWriter(OutputStream outputStream, boolean flushOnNewline)

Here outputStream is an object of type OutputStream




Patrick Healy

Here, outputStream is an object of type OutputStream.

flushOnNewLine controls whether Java flushes the output stream

every time a println( ) method is called.

If flushOnNewLine is true flushing automatically takes place.

If flushOnNewLine is false, flushing is not automatic.



To write to the console (monitor) using a PrintWriter, specify

System.out for the output stream and flush the stream after each call to

println( ).




Patrick Healy

For example, the following line of code creates a PrintWriter that isconnected to console (monitor) output.

PrintWriter pw = new PrintWriter(System.out, true);

The Java program on the next slide demonstrates a PrintWriter



// Demonstrate PrintWriter.

import java.io.*;




Patrick Healy

public class PrintWriterDemo {

public static void main(String[ ] args) {

PrintWriter pw = new PrintWriter(System.out, true);

int i = 120;double d = 123.67;



pw.println("Using a PrintWriter."); // PrintWriter Demo

pw.println(i);

pw.println(d);




Patrick Healy

pw.println(i + " + " + d + " is " + i +d);


} // End of class PrintWriterDemo

The output from the previous program is:

Using a PrintWriter.

120

123.67

120 + 123.67 is 243.67


File Input & Output using Character Streams

In general, to perform character-based file I/O, you will use the

FileReader and FileWriter classes.

Using a FileWriter




Patrick Healy

FileWriter creates a Writer that you can use to write to a file.

FileWriter is derived from OutputStreamWriter and Writer classes

Commonly used constructors are:

FileWriter (String fileName) throws IOException

FileWriter (String fileName, boolean append ) throws IOException

fileName is the full path name of the file. If append is true, then output is

appended to the end of the file. Otherwise, the file is overwritten.


File I / O using Character Streams FileWriter

// A simple keyboard-to-disk utility that demonstrates a FileWriter.

import java.io.*;

public class KtoD {




Patrick Healy

p {



String str;

FileWriter fw;BufferedReader br =

new BufferedReader( new InputStreamReader(System.in));



try {

fw = new FileWriter("test.txt"); // Try to open the file

}




Patrick Healy

}



System.out.println("Cannot open output file.");

return ;}



System.out.println("Enter text ('stop' to quit).");

do {

System.out.print(": ");




Patrick Healy

str = br.readLine( );

if(str.compareTo("stop") == 0) break;

str = str + "\r\n"; // add carriage return & newline

fw.write(str);

} while(str.compareTo("stop") != 0);

fw.close( );

} // End of main ( ) method

} // End of class KtoD


File I / O using Character Streams FileReader

The FileReader class creates a Reader that you can use to read the

contents of a file. FileReader is derived from the InputStreamReader

and Reader classes. It has access to the methods in those classes.




Patrick Healy

The most common constructor is:

FileReader(String fileName) throws FileNotFoundException

where fileName is the full path name of the file.

It throws a FileNotFoundException if the file does not exist.



The following program reads a text file called “test.txt” and displays

the information on the screen.

// A simple disk-to-screen utilitiy that demonstrates a FileReader.




Patrick Healy

import java.io.*;

class DtoS {

public static void main(String[ ] args) throws Exception

{

FileReader fr = new FileReader("test.txt");

BufferedReader br = new BufferedReader(fr);

String s;



while((s = br.readLine()) != null)

{

System.out.println(s);




Patrick Healy

}

fr.close( ); // Close the file


} // End of DtoS class


The File Class: Objectives

To discover file properties, delete and rename files using the File class

To understand how I/O is processed in Java

To distinguish between text I/O and binary I/O




Patrick Healy

To read and write characters using FileReader and FileWriter To improve the performance of text I/O using BufferedReader and BufferedWriter

To write primitive values, strings, and objects as text using PrintWriter and PrintStream

To read and write bytes using FileInputStream and FileOutputStream

To read and write primitive values and strings using DataInputStream/DataOutputStream

To store and restore objects using ObjectOutputStream and ObjectInputStream, and tounderstand how objects are serialized and what kind of objects can be serialized

To use RandomAccessFile for both read and write.


The File Class

The File class is intended to provide an abstraction that deals




Patrick Healy

with most of the machine-dependent complexities of files and

path names in a machine-independent fashion. The filename is

a string.

The File class is a wrapper class for the file name and itsdirectory path.


java.io.File

+File(pathname: String)

+File(parent: String, child: String)

+File(parent: File, child: String)

+exists(): boolean

+canRead(): boolean

+canWrite(): boolean

i Di t () b l

Creates a File object for the specified pathname. The pathname may be adirectory or a file.

Creates a File object for the child under the directory parent. child may be a

filename or a subdirectory.

Creates a File object for the child under the directory parent. parent is a File

object. In the preceding constructor, the parent is a string.

Returns true if the file or the directory represented by the File object exists.

Returns true if the file represented by the File object exists and can be read.

Returns true if the file represented by the File object exists and can be written.

R t t if th Fil bj t t di t

Obtaining file properties and manipulating file




Patrick Healy

+isDirectory(): boolean

+isFile(): boolean

+isAbsolute(): boolean

+isHidden(): boolean

+getAbsolutePath(): String

+getCanonicalPath(): String

+getName(): String

+getPath(): String

+getParent(): String

+lastModified(): long

+delete(): boolean

+renameTo(dest: File): Boolean

Returns true if the File object represents a directory.

Returns true if the File object represents a file.

Returns true if the File object is created using an absolute path name.

Returns true if the file represented in the File object is hidden. The exact

definition of hidden is system-dependent. On Windows, you can mark a file

hidden in the File Properties dialog box. On Unix systems, a file is hidden if its name begins with a period character '.'.

Returns the complete absolute file or directory name represented by the File

object.

Returns the same as getAbsolutePath() except that it removes redundantnames, such as "." and "..", from the pathname, resolves symbolic links (on

Unix platforms), and converts drive letters to standard uppercase (on Win32

platforms).

Returns the last name of the complete directory and file name represented by

the File object. For example, new File("c:\\book\\test.dat").getName() returnstest.dat.

Returns the complete directory and file name represented by the File object.

For example, new File("c:\\book\\test.dat").getPath() returns c:\book\test.dat.

Returns the complete parent directory of the current directory or the file

represented by the File object. For example, newFile("c:\\book\\test.dat").getParent() returns c:\book.

Returns the time that the file was last modified.

Deletes this file. The method returns true if the deletion succeeds.

Renames this file. The method returns true if the operation succeeds.


Example Using the File Class TestFileClass.java

Objective: Write a program that demonstrates how to create

files in a platform-independent way and use the methods in the

File class to obtain their properties. Figure 1 shows a sample

f th Wi d d Fi 2 l




Patrick Healy

run of the program on Windows, and Figure 2 a sample run onUnix

(Windows) (Unix)


The File Class and Processing External Files

The File class provides an abstraction that deals with most of the

machine-dependent complexities of files and path names in a machine-

independent fashion.




Patrick Healy

You can create a new File object using the following statement:

File myfile = new File (“myfile.dat”);

You can use the File class to check properties of files, such as whether

the file exists, or is readable, or updateable.



You can use the getName( ) method to get the name of the file.

For example,

if (myfile.exists( ) )




Patrick Healy

System.out.println(“File “ + myfile.getName( ) + “ already exists”);

The following statement creates a file using the full path using the

Windows operating system:

File myfile = new File(“C: \\Java\\myfile.data”);



You can use the getPath( ) method to get the full path of the file and

the getParent( ) method to get the directory that contains the file.

For example,

if (myfile exists( ) )




Patrick Healy

if (myfile.exists( ) )

{

System.out.println(“The full path is “ + myfile.getPath( ) );

System.out.println(“The directory is “ + myfile.getParent( ) );

}


Demo Program: TestFileClass.java // TestFileClass.java: Demonstrate the File class Chapt 18 I/O ITP120

import java.io.*;

import java.util.*;

public class TestFileClass {

bli i id i (S i [] ) {




Patrick Healy

public static void main(String[] args) {

// Create a File object

File file = new File(".", "images" + File.separator + "bill_gates.gif");

System.out.println("Does it exist? " + file.exists());

System.out.println("Can it be read? " + file.canRead());

System.out.println("Can it be written? " + file.canRead());System.out.println("Is it a directory? " + file.isDirectory());

System.out.println("Is it a file? " + file.isFile());

System.out.println("Is it absolute? " + file.isAbsolute());

System.out.println("Is it hidden? " + file.isHidden());

System.out.println("What is its absolute path? " +

file.getAbsolutePath());


Demo Program: TestFileClass.java try {

System.out.println("What is its canonical path? " +

file.getCanonicalPath());

}

catch (IOException ex) { }




Patrick Healy

System.out.println("What is its name? " + file.getName());

System.out.println("What is its path? " + file.getPath());

System.out.println("When was it last modified? " +

new Date(file.lastModified()));

System.out.println("What is the path separator? " +

File.pathSeparatorChar);

System.out.println("What is the name separator? " +

File.separatorChar);

}

}


Processing External Files

Again, you must use file streams to read from or write

to a disk file.




Patrick Healy

Once again, you can use FileInputStream or

FileOutputStream for byte streams.

And you can use FileReader or FileWriter for character

streams.


File I/O Stream Constructors To create a file stream, use these constructors:

public FileInputStream (String filenameString) // Byte stream constructors

public FileInputStream (File file)




Patrick Healy

public FileOutputStream (String filenameString) // Byte stream constructor

public FileOutputStream (File file)

public FileReader (String filenameString) // Character stream constructors

public FileReader (File file)

public FileWriter (String filenameString) // Character stream constructor

public FileWriter (File file)


File I/O Stream Constructors

Constructing instances of FileInputStream , FileOutputStream ,FileReader, and FileWriter from file names:




Patrick Healy

FileInputStream infile = new FileInputStream("in.dat");

FileOutputStream outfile = new FileOutputStream("out.dat");

FileReader infile = new FileReader("in.dat");

FileWriter outfile = new FileWriter("out.dat");


Demo Program: TestFileReader.java // TestFileReader.java Chapter 18 I/O ITP 120

import java.io.*;

public class TestFileReader {

public static void main(String[ ] args) {




Patrick Healy

public static void main(String[ ] args) {FileReader input = null;

try {

// Create an input stream

input = new FileReader("temp.txt");

int code;

// Repeatedly read a character and display it on the console

while ((code = input.read()) != -1)

System.out.print((char)code);



Demo Program: TestFileReader.java System.out.println("File temp.txt does not exist");

}

catch (IOException ex) {

ex.printStackTrace();

}




Patrick Healy

}finally {

try {

input.close(); // Close the stream

}

catch (IOException ex) {ex.printStackTrace();

}

}

} // End of class TestFileReader


Demo Program: TestFileWriter.java // TestFileWriter.java Chapter 18 File I/O ITP 120

import java.io.*;

public class TestFileWriter {

public static void main(String[ ] args) throws IOException {




Patrick Healy

public static void main(String[ ] args) throws IOException { // Create an output stream to the file

FileWriter output = new FileWriter("temp.txt", true);

// Output a string to the file

output.write(“ NVCC Introduction to Java Programming ITP 120 !!!");

// Close the stream

output.close();

}

}



FileInputStream fis [0]




Patrick Healy

FileInputStream fis

programargs[1]

args[0]

FileOutputStream fos


Processing External Files The previous diagram shows that:

FileInputStream, fis, is used to read data (bytes) from a file

FileOutputStream fos is used to write data (bytes) to a file




Patrick Healy

FileOutputStream, fos, is used to write data (bytes) to a file

Command line:

java CopyFileUsingByteStream f1.txt f2.txt

See the Java program CopyFileUsingByteStream on the following

slides


Processing External Files // CopyFileUsingByteStream.java For Copying files (byte streams)

import java.io.*;

public class CopyFileUsingByteStream

{




Patrick Healy

{

// Main method: args[0] for sourcefile and args[1] for target file


{ // Declare input and output file streams

FileInputStream fis = null;

FileOutputStream fos = null;



if (args.length !=2) // args[0] is source file

{ // args[1] is target file




Patrick Healy

{ g [ ] gSystem.out.println(

"Usage: java CopyFileUsingByteStream f1 f2");

System.exit(0); // Stop the program

}


Processing External Files try

{

// Create file input stream

fis = new FileInputStream(new File(args[0]));




Patrick Healy

// Create file output stream if the file does not exist

File outFile = new File(args[1]);

if (outFile.exists())

{

System.out.println("file " + args[1] + " already exists");

return;

}


Processing External Files else

fos = new FileOutputStream(args[1]); // FileOutputStream

// Display the file size




Patrick Healy

p y

System.out.println("The file " + args[0] + " has "+

fis.available() + " bytes");


Processing External Files // Continuously read a byte from fis and write it to fos

int r;

while ((r = fis.read()) != -1) // EOF is -1

fos.write((byte)r);




Patrick Healy

(( y ) );

}

catch (FileNotFoundException ex)

{

System.out.println(“Error: “ + ex.getMessage( ) );

System.out.println("File not found: " + args[0]);

}


Processing External Files catch (IOException ex)

{

System.out.println(“Some IO Exception occurred”);

System.out.println(“Error: “ + ex.getMessage( ));




Patrick Healy

y p ( g g ( ));

}

Continues to next slide


Processing External Files finally

{

try

{

if (fis != null) fis.close(); // Close the input & output files




Patrick Healy

if (fos != null) fos.close();

}

catch (IOException ex)

{


}

} // End of finally block


} // End of class CopyFileUsingByteStream


Filter Streams Filter streams are streams that filter bytes or characters for some

purpose.

If you want to read integers, doubles, or Strings, you need a filter class

to wrap the input stream.




Patrick Healy

Using a filter class enables you to read integers, doubles, and strings

instead of bytes and characters.

Use FilterInputStream and FilterOutputStream when you need to

process primitive numeric types.


Filter Streams To process strings, use BufferedReader and PushbackReader to filter

characters.

Note: FilterInputStream and FilterOutputStream are abstract classes.




Patrick Healy


FilterInputStream subclasses DataInputStream handles binary formats for all primitive data types.

BufferedInputStream gets data from the buffer and then reads them

from the stream if necessary.




Patrick Healy

LineNumberInputStream keeps track of how many lines are read.

PushBackInputStream allows single-byte look-a-head. Looks at a byte

and pushes it back to the stream if the byte read is NOT the desired

byte.


FilterOutputStream subclasses

DataOutputStream outputs the binary formats for all primitive data

types which is useful if another program uses the output .

BufferedOutputStream outputs to the buffer first and then to the

stream if necessary. You may also call the flush( ) method to write the




Patrick Healy

buffer to the stream.

PrintStream outputs the Unicode format of all primitive types which is

useful if the format is output to the console.


Data Streams (bytes)

The data streams (DataInputStream and DataOutputStream )

read and write Java primitive types in a machine-independent

fashion.




Patrick Healy

This enables you to write a data file for one computer

and read it on another computer that has a different operating

system or file structure.

Class #15 – Input and OutputDataInputStream Methods defined in the DataInput

Interface

int readByte() throws IOException

int readShort() throws IOException

int readInt() throws IOException




Patrick Healy

int readLong() throws IOException

float readFloat() throws IOException

double readDouble() throws IOException char readChar() throws IOException

boolean readBoolean() throws IOException

String readUTF() throws IOException

Class #15 – Input and OutputDataOutputStream Methods defined in the DataOutput

interface

void writeByte(byte b) throws IOException

void writeShort(short is) throws IOException

void writeInt(int i) throws IOException void writeLong(long l) throws IOException




Patrick Healy

void writeLong(long l) throws IOException

void writeFloat(float f) throws IOException

void writeDouble(double d) throws IOException

void writeChar(char c) throws IOException

void writeBoolean(boolean b) throws IOException

void writeBytes(String s) throws IOException

void writeChars(String s) throws IOException

void writeUTF(String s) throws IOException


DataInputStream & DataOutput Stream

Constructors

Data streams are used as wrappers on existing input and

output streams to filter data in the original stream.




Patrick Healy

DataInputStream infile = newDataInputStream(new FileInputStream("in.dat"));

The above creates an input file for in.dat.

DataOutputStream outfile = newDataOutputStream(new FileOutputStream("out.dat"));

The above creates an output file for out.dat.


Using Data Streams The next example shows a program that:

1) Creates 10 random integers,

2) Stores them in a data file,




Patrick Healy

3) Retrieves data from the file,

4) Displays the integers on the console.

See next slide


Using Data Streams Demo Example // TestDataStreams.java: Create a file, store it in binary form, and

// display the contents of the file on the console

import java.io.*;

public class TestDataStreams




Patrick Healy

{

// Main method


{

// Declare data input and output streams

DataInputStream dis = null;

DataOutputStream dos = null;


Using Data Streams Demo Example // Construct a temp file

File tempFile = new File("mytemp.dat");

// Check if the temp file exists

if ( Fil i ())




Patrick Healy

if (tempFile.exists())

{

System.out.println("The file mytemp.dat already exists,"

+" delete it, rerun the program");

System.exit(0);

}


Using Data Streams Demo Example // Write data

try

{

// Create data output stream for tempFile

d D t O t tSt (




Patrick Healy

dos = new DataOutputStream(new

FileOutputStream(tempFile));

for (int i=0; i<10; i++)

dos.writeInt((int)(Math.random()*1000));

}


Using Data Streams Demo Example catch (IOException ex)

{

System.out.println(ex.getMessage( ) );

}

finally




Patrick Healy

{

try

{

if (dos != null) dos.close( ); // Close the file(s)

}


{ System.out.println(“Error: “ + ex.getMessage( ) ); }


Using Data Streams Demo Example // Read data

try

{

// Create data input stream

di D t I tSt ( Fil I tSt (t Fil ))




Patrick Healy

dis = new DataInputStream(new FileInputStream(tempFile));

for (int i=0; i<10; i++)

System.out.print(" "+dis.readInt ( ) ); // Display the integers

}


Using Data Streams catch (FileNotFoundException ex)

{

System.out.println("File not found“ + ex.getMessage( ) ););

}





Patrick Healy


{

System.out.println(ex.getMessage());

}


Using Data Streams finally

{

try

{

if (dis != null) dis.close( ); // Close the file(s)

}




Patrick Healy

}


{

System.out.println(“Error: “ + ex.getMessage( ) ));

}



} // End of class TestDataStreams


Using Data Streams Demo Example The previous Java program TestDataStreams.java creates a

DataInputStream object named “dis” wrapped on FileInputStream and

creates a DataOutputStream object “dos” wrapped on

FileOutputStream

Conceptually,




Patrick Healy

Program DataInputStream dis <-- fileInputStream <--mytemp.dat

DataOutputStream dos fileOutputStreammytemp.dat

The program uses a temporary file, mytemp.dat , to store data.

The program creates mytemp.dat if it does not exist and writes 10 random

integers into mytemp.dat. The data in mytemp.dat is in binary format.




File Class

File class provides functionality for working directly with files in the operating

system

The File class provides overloaded constructors for creating File objects. A File

object can be created by giving the name of the file:

File inputFile = new File(“in.dat”); // Same directory File myInputFile = new File(“C:\\myDirectory\\in.dat”);

A Fil Obj t f t ith fil di t




Patrick Healy

A File Object can refer to either a file or directory

File theDir = new File(“C:\\myDir”); //File object theDir refers to a directory

Some File class methods:

exists() that tests if the named file already exist. mkdir( String st ) for creating directories

list() for listing the contents of directories

getPath() gets the path of the named file

length() returns the file size in bytes


File Class

Example: DirectoryContents.java listing the contents of a directory using File class

import java.io.*;

public class DirectoryContents

{

public static void main(String[ ] args){




Patrick Healy

File myDir = new File(“C: \\");

if(myDir.isDirectory( ) ) {

System.out.println("Contents of directory " + myDir );

String[ ] contents = myDir.list();

for( int I = 0; I < contents.length; I++)

System.out.println(contents[ I ] );

} // End of “if” block


} // End of class DirectoryContents


Using Java I/O

Many of the methods including constructors of Java.io

classes throw exceptions:

The most commonly thrown is IOException.

Reading data from the keyboard

BufferedReader in




Patrick Healy

BufferedReader in

= new BufferedReader(new InputStreamReader(System.in);

An InputStreamReader is like an adapter, it reads bytestreams and converts it into character streams

BufferedReader wraps the InputStreamReader to provide extrafunctionality, allowing to buffer the input to support readLine()


Using Java I/O

Example Reading strings from the keyboard

Import java.io.*

public class ReadStringFromKeyboard {


{ // Converts from bytes to charactersBufferedReader in = new BufferedReader(new InputStreamReader (System.in));




Patrick Healy

String yourInput;

try {

System.out.println("Please enter any string and hit the return key when done:");

yourInput = in.readLine( );

System.out.println("\nBelow is the input you entered");

System.out.println(yourInput);

}

catch (IOException ex) { System.out.println(“Could not read from the keyboard” }


} // End of class ReadStringFromKeyboard


Using Java I/O

Example: Reading from an external file

public class ReadFromFile {


{

String st = null;

File inputFileName = null;

FileReader inputFile = null;




Patrick Healy

FileReader inputFile null;

BufferedReader in = null;

try {

inputFileName = new File("Input1.txt");

inputFile = new FileReader(inputFileName);

in = new BufferedReader(inputFile);

/* Note: The above 3 lines can be combined in one line as below

in = new BufferedReader(new FileReader(new File("Input1.txt"))); */


Using Java I/O

Example Continued

// Now let us start reading from the opened file

while((st = br.readLine()) != null )

{

System.out.println(st); // Print the string

}

}




Patrick Healy

}

catch (FileNotFoundException fnex)

{ System.out.println(“Error: “ + fnex.getMessage( ) );

System.out.println("Input file was not found");

}

catch (IOException ex) { System.out.println(“Error: “ + ex.getMessage( ) );

System.out.println("There was a problem reading from the file");

}


Using Java I/O

Example continued

finally

{

if( br != null)

try {

br.close( ); // Close the file




Patrick Healy

}

catch (Exception ex) {


System.out.println("There was a problem with closing the file");

}

} // End finally block


} // End of class


Print Streams The data output stream outputs a binary representation of data, so

you cannot view its contents as text.

In Java, you can use print streams to output data into files. Thesefiles can then be viewed as text.




Patrick Healy

The PrintStream and PrintWriter classes provide the

functionality for doing this.

PrintStream is for bytes

PrintWriter is for characters (Unicode)


Print Streams: PrintWriter Constructors

PrintWriter(Writer out)

PrintWriter(Writer out, boolean autoFlush)

PrintWriter(OutputStream out) PrintWriter(OutputStream out, boolean autoFlush)




Patrick Healy


Print Streams: PrintWriter Methods (for chars)

void print(Object o)

void print(String s)

void println(String s)

void print(char c)

void print(char[] cArray)




Patrick Healy

p y

void print(int i)

void print(long l)

void print(float f) void print(double d)

void print(boolean b)


Print Streams: PrintWriter Methods

Note:

On the previous slide, you may replace print with println in the various

method definitions.

The println method, which prints the object, is followed by a new line.




Patrick Healy

When the object is passed to print or println,

the object‟s toString( ) method converts it to a String object.


Demo Program Example Using Print Streams

The next sample Java program creates a print stream, pw , of

PrintWriter , wrapped on FileOutputStream, for text format.

pw = new PrintWriter(new FileOutputStream(tempFile),true);




Patrick Healy

The program creates the file, arg[0], if that file does not already exist.

The program writes 10 random integers into the file by using the data

output stream, then closes the stream. The data file could be viewed by using the type command in DOS


Using Print Streams: Demo Example

// TestPrintWriters.java: Create a text file

// using PrintWriter

import java.io.*;

public class TestPrintWriters{

// Main method: args[0] is the output file




Patrick Healy

// Main method: args[0] is the output file

public static void main(String[] args)

{// Declare print stream

PrintWriter pw = null;


Using Print Streams: Demo example

// Check usage

if (args.length != 1)

{

System.out.println("Usage: javaTestPrintWriters file");




Patrick Healy

System.exit(0);

}

File tempFile = new File(args[0]);



if (tempFile.exists())

{

System.out.println("The file " + args[0] +

" already exists, delete it, rerun the program");

S t it(0)




Patrick Healy

System.exit(0);

}



// Write data

try

{

// Create print writer stream for tempFile pw = new PrintWriter(new

Fil O t tSt (t Fil ) t )




Patrick Healy

FileOutputStream(tempFile), true);

for (int i=0; i<10; i++)

pw.print(" "+(int)(Math.random()*1000));}




{


}finally

{




Patrick Healy

{

// Close files

if (pw != null) pw.close();}

}

}



C:\test>java TestPrintWriters

Usage: java TestPrintWriters filename

C:\test>java TestPrintWriters test.dat




Patrick Healy

C:\test>type test.dat (Use the TYPE command to see data in file)

567 915 7 23 677 455 402 997 290 549


Print Streams




Patrick Healy

PrintWriter

program args[0]

FileOutputStream




Using Java I/O

Example: WriteToFile.java (continued)

public static void main (String[ ] args)

{

File outputFileName = null;

PrintWriter outToFile = null;

try {




Patrick Healy

outputFileName = new File("outFile1.txt");

outToFile = new PrintWriter( new FileWriter(outputFileName));

// Now we can start writing to fileoutToFile.println("This message is going to the output file");

outToFile.println("This will be line two in the output file");

outToFile.println("We can write the output file any time we want");

outToFile.flush( ); // Flush output file

}


Using Java I/O

Example 18.6



System.out.println("There was a problem writing to the output file");

}

finally {




Patrick Healy

y {

if ( outToFile != null )

outToFile.close( ); // Close output file



} // End of class WriteToFile


Buffered Streams in Java

Java introduces buffered streams that speed up input and output

by reducing the number of reads and writes. In the case of input, a

bunch of data is read all at once instead of one byte at a time.

In the case of output, data are first cached into a buffer, thenwritten all together to the file.




Patrick Healy

Using buffered streams is highly recommended.


Buffered Stream Constructors

BufferedInputStream (InputStream in)

BufferedInputStream (InputStream in, int bufferSize)

BufferedOutputStream (OutputStream in)

BufferedOutputStream (OutputStream in, int bufferSize)

BufferedReader(Reader in)




Patrick Healy

BufferedReader(Reader in, int bufferSize)

BufferedWriter(Writer out)

BufferedWriter(Writer out, int bufferSize)

Class #15 – Input and OutputDemo Program: ViewFile.java (A Text Viewer program)

This case study writes a program that views a text file in a text area. The

user enters a filename in a text field and clicks the View button; the file is

then displayed in a text area.




Patrick Healy


Buffered Streams in Java ViewFile program

// ViewFile.java: Read a text file and store it in a text area

import java.awt.*; // Buffered I/O example (Demo program)

import java.awt.event.*;

import java.io.*;

import javax.swing.*;




Patrick Healy

public class ViewFile extends MyFrameWithExitHandling

implements ActionListener

{

// Button to view view

private JButton jbtView = new JButton("View");





// Constructor

public ViewFile()

{

// Panel p to hold a label, a text field, and a button

Panel p = new Panel();

p.setLayout(new BorderLayout());




Patrick Healy

p.add(new Label("Filename"), BorderLayout.WEST);

p.add(jtf, BorderLayout.CENTER);

jtf.setBackground(Color.yellow);

jtf.setForeground(Color.red);

p.add(jbtView, BorderLayout.EAST);





// Handle the "View" button

public void actionPerformed(ActionEvent e){

if (e getSource() == jbtView)




Patrick Healy

if (e.getSource() jbtView)

showFile();

}



// Display the file in the text area

private void showFile()

{

// Use a BufferedStream to read text from the fileBufferedReader infile = null;




Patrick Healy

// Get file name from the input text field at the bottom

String filename = jtf.getText().trim();

String inLine;



try

{

// Create a buffered stream

infile = new BufferedReader(new FileReader(filename));

// Read a line




Patrick Healy

// Read a line

inLine = infile.readLine();

boolean firstLine = true;



while (inLine != null) // Append the line to the text area

{

if (firstLine) {

firstLine = false;

jtaFile.append(inLine); }

else

{




Patrick Healy

{

jta.append("\n" + inLine); }

inLine = infile.readLine();

}




catch (FileNotFoundException ex)

{ System.out.println(“Error: “ + ex.getMessage( ) );

System.out.println("File not found: " + filename);

}catch (IOException ex)

{




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{


}



finally

{

try

{

if (infile != null) infile.close( ); // Close input file

}





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{

System.out.println(“Error: “ + ex.getMessage( )); }


} // End of method showFile()

} // End of class ViewFile



Demostrate the ViewFile program by running:

java ViewFile (at the command prompt)

Wait for Java window to appear.




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pp

then type Comcast1.txt or the name of some text file in the text box at the

bottom of the Java window.

Look at the contents on the text file in the Java window.


Text Input & Output on the Console

In previous chapters, you used text input and output with the System

class. The System class, as you have already seen, contains 3 I/O

objects: System.in, System.out, and System.err . The objects in, out

and err are static variables.

The variable in is of InputStream type and out , err are of PrintStream

type. (byte streams)




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yp ( y )

These are the basic objects that all java programmers use to get inputfrom the keyboard, send output to the screen, and display error

messages.



To perform console output, you can use any of the methods for

PrintStream in the System.out object.

To get input from the keyboard, you can use the following statements to

read a string from the keyboard

S t lid




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See next slide

AND ALSO VIEW THE EXPANDED VERSION of MyInput.java which

follows thereafter



BufferedReader br

= new BufferedReader(new InputStreamReader(System.in), 1);

// Note: the 1 above means a buffer size of 1

// Declare and initialize the string String string = " ";

// Get the string from the keyboard




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try

{ string = br.readLine(); }


System.out.println(ex); }


Text I/O on the Console MyInput.java (full)

public class MyInput // Expanded version

{ // Read a string from the keyboard

public static String readString()

{

BufferedReader br = new BufferedReader(new InputStreamReader(System.in), 1);

// Declare and initialize the string




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String string = " ";

// Get the string from the keyboard

try {

string = br.readLine(); }


System.out.println(ex) ; }



// Return the string obtained from the keyboard

return string;

}

// Read an int value from the keyboard

public static int readInt()




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{

return Integer.parseInt(readString());

}





// Read a short value from the keyboard

public static double readShort()

{

return Short.parseShort(readString());

}

// Read a long value from the keyboard




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// Read a long value from the keyboard

public static double readLong()

{

return Long.parseLong(readString());

}



// Read a float value from the keyboard

public static double readFloat()

{

return Float.parseFloat(readString());}

}




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Random Access Files (byte streams)

Java allows you to access the contents of a file in random order

To do this, you will use RandomAccessFile which encapsulates a

random-access file.

RandomAccessFile is a stream class derived from Object

RandomAccessFile is NOT derived from InputStream or OutputStream.

RandomAccessFile implements interfaces InputData & OutputData

InputData & OutputData define the basic I/O methods




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InputData & OutputData define the basic I/O methods.

You can also position the file pointer within the file using the methodseek ( )


Random Access Files (Constructor(s))

The constructor for RandomAccessFile is:

RandomAccessFile (String filename, String access)

throws FileNotFoundException

The name of the file is passed in filename




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The term access determines what type of file access is permitted.

If the access is “r”, the file is read-only.

If the access is “rw”, the file is opened in read-write mode.


Random Access Files (Methods)

The method seek ( ) is used to set the current position of the file

pointer within a random access file:

void seek (long newpos) throws IOException

newpos specifies the new position, in bytes, of the file pointer from

the beginning of the file




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the beginning of the file.

After a call to seek( ), the next read or write operation will occur at the

new file position.


Random Access Files (Methods)

public long getFilePointer ( ) throws IOException



public long length ( ) throws IOException

Returns the length of the file in bytes.

public final void writeChar (int v) throws IOException

Writes a character to the file as a 2 byte Unicode character with the




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Writes a character to the file as a 2-byte Unicode character with the

higher byte written first.

public final void writeChars(String s) throws IOException

Writes a string to a file as a sequence of characters.


Random Access Files

RandomAccessFile implements the read ( ) and write ( ) methods.

It also implements the InputData and OutputData interfaces, which

means that methods to read and write the simple data types such as

readInt( ) and writeDouble( ) are available.

The slides which follow show a Java program that demonstrates random




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p g

access file I/O. The program writes 6 double numbers to a file and

then reads them back in a non-sequential order.


Random Access Files

// Demonstrate random access files RandonAccessDemo.java

import java.io.*;

public class RandomAccessDemo {






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double data[ ] = { 19.4, 10.1, 123.54, 33.0, 87.9, 74.25 };double d;

RandomAccessFile raf;


Random Access Files

try {

raf = new RandomAccessFile("random.dat", "rw");

}

catch(FileNotFoundException ex)

{

System.out.println("Cannot open file.");

S t t i tl (“E “ + g tM g ( ) )




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return ;}


Random Access Files

// Write values to the file.

for (int i=0; i < data.length; i++) {

try {

raf.writeDouble(data[i]);

}

catch(IOException ex) {

System.out.println(“Error: “ + ex.getMessage( ));




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System.out.println("Error writing to file.");

return ; }

} // End of “for” loop


Random Access Files

try {

// Now, read back specific values

raf.seek(0); // seek to first double

d = raf.readDouble();System.out.println("First value is " + d);

raf.seek(8); // seek to second double

d = raf.readDouble();




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d a ead oub e();

System.out.println("Second value is " + d);

raf.seek(8 * 3); // seek to fourth double


System.out.println("Fourth value is " + d);

System.out.println();


Random Access Files

// Now, read every other value.

System.out.println("Here is every other value: ");

for (int i=0; i < data.length; i+=2) {

raf.seek(8 * i); // seek to ith double


System.out.print(d + " ");

} // End of “for” loop




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} // End of for loop



Random Access Files

catch(IOException exc)

{


System.out.println("Error seeking or reading.");

}

raf.close( ); // Close the file

} // End of main ( )




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} // End of main ( )

} // End of class RandomAccessDemo


Random Access Files

Output from the previous Java program RandomAccessDemo:

First value is 19.4

Second value is 10.1

Fourth value is 33.0

Here is every other value:




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Here is every other value:

19.4 123.54 87.9


Case Studies: Address Book

Now let us use RandomAccessFile to create a useful project for storing and viewing and

address book. The user interface of the program is shown in Figure 16.24. The Add button

stores a new address to the end of the file. The First , Next , Previous, and Last buttons

retrieve the first, next, previous, and last addresses from the file, respectively.




Patrick Healy


Parsing Text Files

The StreamTokenizer class lets you take an input stream and parse it into

words, which are known as tokens.

The tokens are read one at a time.

The following is the StreamTokenizer constructor:

StreamTokenizer st =




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StreamTokenizer st =StreamTokenizer(Reader is)


StreamTokenizer Constants TT_WORD

The token is a word.

TT_NUMBER

The token is a number.

TT_EOL

The end of the line has been read.

TT EOF




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TT_EOF

The end of the file has been read.


StreamTokenizer Variables int ttype (token type)

Contains the current token type, which matches one of the constants listed on

the preceding slide.

double nvalContains the value of the current token if that token is a number.

String sval

Contains a string that gives the




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g g

characters of the current token if that

token is a word.


StreamTokenizer Methods

public int nextToken() throws IOException

Parses the next token from the input stream of this StreamTokenizer.

The type of the next token is returned in the ttype

field.

If ttype == TT_WORD, the token is stored in sval;




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_

if ttype == TT_NUMBER , the token is stored in nval.


Example : Demo program Using StreamTokenizer Demo: ParsingTextFile.java

in.dat

James 32 60 30

George 100 100 100

John 90 94 100

out.dat

James 39.6

George 100.0

John 95.2

+

30%

30%

40%




Patrick Healy


ParsingTextFile.java (Demo program)

// ParsingTextFile.java: ITP 120 // Process text file using StreamTokenizer Chapter 18 I/O

import java.io.*;

public class ParsingTextFile

{ // Main method

public static void main(String[] args)

{

// Declare file reader and writer character (2 bytes) streams




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// Declare file reader and writer character (2 bytes) streams

FileReader frs = null;FileWriter fws = null;

// Declare streamTokenizer

StreamTokenizer in = null;


ParsingTextFile.java (Demo)

// Declare a print stream

PrintWriter out = null;

// For input file fields: student name, midterm1,

// midterm2, and final exam score

String sname = null;

double midterm1 = 0;double midterm2 = 0;

double finalScore = 0;

// Computed total score

double total = 0;




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;

try

{

// Create file input and output streams

frs = new FileReader("grades.dat");

fws = new FileWriter("gradesout.dat");



// Create a stream tokenizer wrapping file input stream

in = new StreamTokenizer(frs);

out = new PrintWriter(fws); // Create PrintWriter object

// Read first token

in.nextToken();

// Process a record // TTs are Tokenizer constants

while (in.ttype != in.TT_EOF) // TT_EOF means end of file

{




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{

// Get student nameif (in.ttype == in.TT_WORD) // TT_WORD means token is a word

sname = in.sval;

else

System.out.println("Bad file format");



// Get midterm1

if (in.nextToken() == in.TT_NUMBER) //TT_NUMBER means token is a number

midterm1 = in.nval;

else


// Get midterm2 score

if (in.nextToken() == in.TT_NUMBER)

midterm2 = in.nval;

else




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else


// Get final exam score

if (in.nextToken() == in.TT_NUMBER)

finalScore = in.nval;



total = midterm1*0.3 + midterm2*0.3 + finalScore*0.4;

out.println(sname + " " + total);

in.nextToken( );

}

}catch (FileNotFoundException ex)

{

System.out.println("Error: " + ex.getMessage());

System.out.println("File not found: in.dat");




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System.out.println( File not found: in.dat );

}catch (IOException ex)

{


}



finally // Always execute finally block{

try

{

if (frs != null) frs.close();

if (fws != null) fws.close();

}


{

System.out.println(ex);

}




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}

}System.out.println("To view input file, TYPE GRADES.DAT");

System.out.println("To view output file, TYPE GRADESOUT.DAT");


} // End of class



ReadBytes.java

WriteDemo.java

ShowFile.java

CopyFile.java CopyFileUsingByteStream.java

CompFile.java

RWData.java

RandomAccessDemo.java




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PrintWriterDemo.javaReadChars.java

ReadLines.java



TestDataStreams.java

TestFileClass.java

TestPrintWriters.java

ViewFile.java (cute file viewer program)

ParsingTextFile.java

TestRandomAccessFile.java needs these class files:

AddressBook.java

FixedLengthStringIO class




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FixedLengthStringIO.class



TestDataStream.java

TestFileClass.java

TestFileReader.java

TestFileStream.java

TestFileWriter.javaTestObjectStreamForArray.java

TestObjectInputStream.java

TestObjectOutputStream.java

AddressBook java (with FixedLengthStringIO java)




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AddressBook.java (with FixedLengthStringIO.java)

Other created or required files: object.dat, temp.txt, student.dat


End of Presentation




Patrick Healy

java io correcto

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