Java IOand

C++ StreamsOctober 22, 2004

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Outline

Java IO

InputStream/OutputStream

FilterInputStream/FilterOutputStream

DataInputStream/DataOutputStream

Reader/Writer

Encodings

C++ Streams

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java.io - IntroTwo main abstractions:

streams of bytesInputStream

abstract classis the superclass of all classes representing aninput stream of bytes

OutputStreamabstract classis the superclass of all classes representing anoutput stream of bytes

streams of characters

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java.io - IntroTwo main abstractions:

streams of bytes

streams of charactersReader

abstract classis the superclass of all classes representing aninput stream of characters

Writerabstract classis the superclass of all classes representing anoutput stream of characters

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OutputStreammust always provide at least a method that writes onebyte of output

methods:

void close()void flush()void write(byte[] b)void write(byte[] b, int off, int len)abstract void write(int b)

subclasses

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OutputStream (cont)subclasses:

ByteArrayOutputStreamdata is written into a byte arraythe buffer automatically grows as data is written toit

FileOutputStreamwriting data to a File or to a FileDescriptormeant for writing streams of raw byte

FilterOutputStreamObjectOutputStreamPipedOutputStream

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OutputStream (cont)subclasses:

ByteArrayOutputStreamFileOutputStreamFilterOutputStream

superclass of all classes that filter output streamssubclasses: BufferedOutputStream,CheckedOutputStream, CipherOutputStream,DataOutputStream, DeflaterOutputStream,DigestOutputStream, PrintStream

ObjectOutputStreamPipedOutputStream

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OutputStream (cont)subclasses:

ByteArrayOutputStreamFileOutputStreamFilterOutputStreamObjectOutputStream

writes primitive data types and graphs of Javaobjectsonly objects that support the java.io.Serializableinterface can be written to streamsprimitive data types can also be written

PipedOutputStreamcan be connected to a piped input stream tocreate a communications pipe

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FilterOutputStreamwrites data to another OutputStream

two kind of subclasses:processing of the data:

BufferedOutputStreamCheckedOutputStreamCipherOutputStreamDeflaterOutputStream· GZIPOutputStream· ZipOutputStreamDigestOutputStream

provides an expanded interface:DataOutputStreamPrintStream: polymorphic print and println, printf

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DataOutputStreamExtended interface provided by DataOutputStream:void writeBoolean(boolean v)void writeByte(int v)void writeBytes(String s)void writeChar(int v)void writeChars(String s)void writeDouble(double v)void writeFloat(float v)void writeInt(int v)void writeLong(long v)void writeShort(int v)void writeUTF(String str)

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OutputStream - ExampleFileOutputStream fileOut =

new FileOutputStream("myfile");// add bufferingBufferedOutputStream bufOut =

new BufferedOutputStream(fileOut);// add compressionGZIPOutputStream gzOut =

new GZIPOutputStream(bufOut);// interface for binary dataDataOutputStream out =

new DataOutputStream(gzOut);// some writingout.writeInt(n);out.writeDouble(d);

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OutputStream - What if?FileOutputStream fileOut =

new FileOutputStream("myfile");BufferedOutputStream bufOut =

new BufferedOutputStream(fileOut);GZIPOutputStream gzOut =

new GZIPOutputStream(bufOut);DataOutputStream out1 =

new DataOutputStream(gzOut);DataOutputStream out2 =

new DataOutputStream(bufOut);

out1.writeInt(n);out2.writeDouble(d);

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OutputStream - What if?FileOutputStream fileOut =

new FileOutputStream("myfile");BufferedOutputStream bufOut =

new BufferedOutputStream(fileOut);GZIPOutputStream gzOut =

new GZIPOutputStream(bufOut);DataOutputStream out1 =

new DataOutputStream(gzOut);DataOutputStream out2 =

new DataOutputStream(bufOut);

out1.writeInt(n);out2.writeDouble(d);

The output will be corrupted!

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OutputStream - A common construction

DataOutputStream out =new DataOutputStream(

new GZIPOutputStream(new BufferedOutputStream(

FileOutputStream("myfile"))));

out.writeInt(n);out.writeDouble(d);

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InputStreamsimilar with OutputStream but in reverse

subclasses:ByteArrayInputStreamFileInputStreamFilterInputStreamObjectInputStreamPipedInputStreamSequenceInputStream

represents the logical concatenation of other inputstreams

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The other world: charactersWriter

methods that a subclass must implement are:write(char[], int, int), flush(), and close()subclasses: BufferedWriter, CharArrayWriter,FilterWriter, OutputStreamWriter, FileWriter,PipedWriter, PrintWriter, StringWriter

Readermethods that a subclass must implement areread(char[], int, int) and close()subclasses: BufferedReader, CharArrayReader,FilterReader, InputStreamReader, PipedReader,StringReader

What is the big difference?

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The other world: charactersWriter

methods that a subclass must implement are:write(char[], int, int), flush(), and close()subclasses: BufferedWriter, CharArrayWriter,FilterWriter, OutputStreamWriter, FileWriter,PipedWriter, PrintWriter, StringWriter

Readermethods that a subclass must implement areread(char[], int, int) and close()subclasses: BufferedReader, CharArrayReader,FilterReader, InputStreamReader, PipedReader,StringReader

What is the big difference? Encodings!

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InputStreamReader/OutputStreamWriter

InputStreamReaderis a bridge from byte streams to character streamsreads bytes and decodes them into characters usinga specified charset

OutputStreamWriterthe opposite of InputStreamReader

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EncodingsJDKTM 5.0 Documentation

→ Tool Docs→ Internationalization Tools

→ native2ascii→ Supported Encodings

docs/guide/intl/encoding.doc.html

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Another Universe:

C++ Streams

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Reference

The C++ Programming Language, Third

Edition by Bjarne Stroustrup. Published by

Addison Wesley Longman, Inc.

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Standard StreamsSeveral standard streams are declared in <iostream>:ostream cout // standard output stream

// of charostream cerr // standard unbuffered output

// stream for error messagesostream clog // standard output stream for

// error messageswostream wcout; // wide stream ver. of coutwostream wcerr; // wide stream ver. of cerrwostream wclog; // wide stream ver. of clog

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istreamProvides:

»get

getline

read

gcount

putback

tie

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ostreamProvides:

«put

write

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Statebool good() const; // next op. might succeedbool eof() const; // end of input seenbool fail() const; // next op. will failbool bad() const; // stream is corruptediostate rdstate() const; // get io state flagsvoid clear(iostate f = goodbit);

// set io state flagsvoid setstate(iostate f) {clear(rdstate()|f); // add f to iostate flags

}operator void*() const; // nonzero if !fail()bool operator!() const {return fail();

}

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Formatingstatic const fmtflagsskipws, // skip whitespace on inputleft // pad after valueright, // pad before valueinternal, // pad between sign and valueboolalpha, // use symbolic representationdec, // base 10 output (decimal)hex, // base 16 output (hexadecimal)oct, // base 8 output (octal)scientific, // d.ddddddEddfixed, // dddd.ddshowbase, // prefix oct by 0 and hex by 0xshowpoint, // print trailing zerosshowpos, // explicit ’+’ for positive intsuppercase; // ’E’, ’X’ rather than ’e’, ’x’

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Formating (cont)// read flagsfmtflags flags() const;// set flagsfmtflags flags(fmtflags f);// add flagsfmtflags setf(fmtflags f) {return flags(flags()|f);

}// clear flagsvoid unsetf(fmtflags mask) {flags(flags()&˜mask);

}

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Manipulatorsdeclared in <iomanip>, namespase std

Manipulators:boolalpha, noboolalphashowbase, noshowbaseshowpoint, noshowpointshowpos, noshowposskipws, noskipws, wsuppercase, nouppercaseinternalleft, rightdec, hex, octfixed, scientific

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Manipulators (cont)Manipulators (cont):

endl, endsflushresetioflags, setioflagssetbasesetfillsetprecisionsetw

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Other kinds of streamsFile Streams

<fstream>ifstream, ofstream, fstream

String Streams<sstream>istringstream, ostringstream, stringstreamwistringstream, wostringstream, wstringstream

Stream Buffers

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That’s all!

Have a nice weekend!

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