© calvin college, 2009 1 all our knowledge brings us nearer to our ignorance, all our ignorance...

© Calvin College, 2009

1

All our knowledge brings us nearer to our ignorance,

All our ignorance brings us nearer to death,But nearness to death, no nearer to God.Where is the Life we have lost in living?Where is the wisdom we have lost in knowledge?Where is the knowledge we have lost in

information?The cycles of Heaven in twenty centuriesBring us farther from God and nearer to the Dust.

- T. S. Eliot, Choruses From ‘The Rock’, Selected Poems

(New York: Harcourt, Brace & World, 1964), p. 107.


2

File Input & Output

● Example● Streams:

– Input Streams– Output Streams– Buffering– Applications

● Database Management Systems● Privacy


3

Example: Analysis● We’d like to modify

the guessing game so that drills students on Chinese Characters.

● A sketch of a solution achieving this goal is shown here.

User’s guess… Give up

Some hint goes here (maybe an image and/or audio)…


4

Example: Design● The design includes the following

classes:

CharacterDrillController

CharacterDrill

+myAnswerIndex+myHintCount

+guess()+reset()+getHintImageFilename()+getHintPronunciationFilename()+getHintText()

Character

+myTranslation+myPinyin+myImageFilename+myPronunciationFilename+mySentenceCharacterDrillTest

*1

CharacterPanel

+setImage()+setPronunciation()


5

Iteration 0

● Analysis

● Design

● Implementation

● Test


6

Limitations of Hard-Coding Data

● Our initial iteration assumes that:– we can code the data directly in the program;– the data never (or rarely) changes;– people who change data know how to program.

● This approach does not scale well to real data-based applications.


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Input & Output Streams

● Input and output in Java is accomplished using stream classes:

Program

Input Stream

Output Stream

Program


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Java Streams

● Simple I/O uses predefined streams:– System.in– System.out– System.err

● Create file streams using:– File– Scanner– PrintWriter


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File● The File class models a system-

independent view of a file comprising:– Filename;– Directory pathname:

• Relative;• Absolute.

● Patterns:new File(pathAndFilenameString)new File(pathnameString, filenameString)


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Scanner● The Scanner class can scan:

– Keyboard input stream;– File;– String.

● Pattern: new Scanner(inputStreamOrFileOrString)

● The API includes these methods:– next() nextInt() nextLine() ...– hasNext() hasNextInt() hasNextLine() ...

– close()


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Iteration 1

● Analysis

● Design

● Implementation

● Test


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Example: File InputGiven: the data filename and pathAlgorithm:

Open a read stream/scanner to the given file.While the file has more tokens:

Read the token.Process the token.

Close the file stream/scanner.

Scanner fileIn = new Scanner(new File(path, filename));

List<Integer> scores = new ArrayList<Integer>();while (fileIn.hasNext()) scores.add(fileIn.nextInt());fileIn.close();System.out.println(scores);


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Iteration 2

● Analysis

● Design

● Implementation

● Test


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Example: Record InputGiven: the data filename and pathAlgorithm:

Open a read stream/scanner to the given file.While the file has more lines:

Read the line.Process the fixed and variant tokens.

Close the file stream/scanner.

Scanner fileIn = new Scanner(new File(path, filename));List<Soldier> soldiers = new ArrayList<Soldier>();while (fileIn.hasNextLine()) soldiers.add(new Soldier(fileIn.nextLine()));fileIn.close();for (int i = 0; i < soldiers.size(); i++) System.out.println(soldiers.get(i));

ReadRecordsConsole

Soldier

+myName+myRank+mySerialNumber+myNicknames

+Soldier(String)+toString()


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Example: Record Input (cont.)public class Soldier {

private String myName, myRank, mySerialNumber; private List<String> myNickNames;

public Soldier(String line) { Scanner scanner = new Scanner(line); myName = scanner.next(); myRank = scanner.next(); mySerialNumber = scanner.next(); myNickNames = new ArrayList<String>(); while (scanner.hasNext()) { myNickNames.add(scanner.next()); } scanner.close(); } // other code...}


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PrintWriter● The PrintWriter class can print

formatted text to a text-output stream.

● Pattern:new PrintWriter(outputFile)

● The API includes these methods:– print() println() ...– printf()– close() flush()


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Iteration 3

● Analysis

● Design

● Implementation

● Test


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Example: Record OutputGiven: the output filename and pathAlgorithm:

Open a print writer stream to the given file.Loop forever:

Prompt for and read a line of data.If the line is the sentinel

Quit.else

Output the line.Close the file stream/scanner.


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Example: Record Output (cont.)

PrintWriter fileOut = new PrintWriter(new File(path, filename));

String line = "";while (true) { System.out.print("enter record (just enter to quit): "); line = keyboard.nextLine(); if (line.equals("")) { break; } else { fileOut.println(line); } }

fileOut.close();System.out.println("data stored to: " + path + filename);


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Buffering

● I/O is slow relative to processing speed, so it is generally buffered.

Program

Input Stream

Output Stream

Program

buffer

buffer


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Java Buffering

● Buffering can be added to file streams to improve the efficiency of I/O operations.

● A buffer is a memory area that stores up input/output data so that it can be input/output all at once.

● Patterns: new BufferedReader(new FileReader(fileNamePath));

new BufferedWriter(new FileWriter(fileNamePath));


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Uses for File I/O

● Using simple text files is unusual, but they are used, e.g.:– Log files;– Configuration files.

● Applications are more likely to use:– Database management systems;– XML files;– Lexing and parsing tools.


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Data Management

● Storing, retrieving and manipulating data sets are very common problems.

● Database Management Systems are designed to address these problems.

Database

Files

Records

Fields

Characters/Strings/Integers

Bits


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The Relational Data Model

● Most current DBMSs use the relational data model.

● Relational models separate the structure of the data from the data itself.

Schema: Data:Field Field Type

name String

rank String

serialNumber String

Name Rank Serial Number

Joe Colonel 1425321

Mary Lieutenant 8375679

Bob Private 2367532


31

Structured Query Language

● SQL is the standard query language for relational databases.

● Example:

SQL> SELECT name, rank FROM SoldierTable WHERE ID > 2000000;

NAME RANK --------- -------- Mary Lieutenant Bob Private


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Edgar F. Codd (1923-2003) Relational Data Model

image from wikipedia, June, 2006

● Codd developed the relational model in the early 1970s.

● Included features for:– Data definition– Data queries

● Most current database systems use the relational model.


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Privacy

● Database systems allow us to build and maintain large data sets:– This can be useful for many applications.– It can also be dangerous.

● Guidelines:– Collect only what you need to collect.– Have a clear policy on what information is

collected and on how it is used.– Keep the data accurate and secure.

What’s theBig Idea

© calvin college, 2009 1 all our knowledge brings us nearer to our ignorance, all our ignorance...

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