Chapter 6 Using Classes: Dates and I/O Streams

Programming and Problem SolvingWith Java

Copyright 1999, James M. Slack

Chapter 6Using Classes: Dates and I/O StreamsDate, DateFormat, GregorianCalendar ClassesReading from Keyboard with Input StreamUsing Streams to Read and Write Text FilesDatabase Management Systems

Programming and Problem Solving With Java 2

Classes: Uses in JavaPackage related group of methods

Example: Math classUse methods with name of the class

int x = Math.abs(y);

Make a new data typeExample: Turtle classMake an object of the class

Turtle myTurtle = new Turtle();

Use methods with objectsmyTurtle.move(100);


Classes: Why Use?Make Java extensible

Can add new features to the languageCan build on existing features, or

start from scratchExample: String class

String not primitive in JavaWorks almost like a primitive type

Many standard classesDates User Interface ExceptionsFiles Networking DatabasesApplets Data storage ElectronicThreads Random numbers commerce


Classes: Why Use?Classes form basis of program developmentGiven problem, Java programmer should

Look for classes appropriate to the problem domain If there are no existing classes

•Extend existing classes, or•Write new classes from scratch

Classes are essence of object-oriented programming


Date Classes: DateThree of Java's many Date

classesDateDateFormatGregorianCalendar

The Date classDate object represents a particular point in timeTo create an object of the class

Date aDate = new Date();

Date constructor initializes with today's date and time

new operatormakes object

Constructor


Date Classes: DateFormatDisplay Date object

Date aDate = new Date();System.out.println(aDate);

Mon Apr 20 16:49:32 CST 1998

DateFormat: format Date object for displayDateFormat is abstract: can't create objects with newTo create a DateFormat object

DateFormat aDateFormatter = DateFormat.getDateInstance();

Use format() method to format a Date objectDate aDate = new Date();DateFormat aDateFormatter = DateFormat.getDateInstance();String aString = aDateFormatter.format(aDate);

20-Apr-1998


Date Classes: DateFormatFour date formats

Specify format in DateFormat.getDateInstance()Date aDate = new Date();DateFormat aDateFormatter = DateFormat.getDateInstance(DateFormat.FULL);String aString = aDateFormatter.format(aDate);

Monday, April 20, 1998

Can specify locale in DateFormat.getDateInstance()DateFormat aDateFormatter = DateFormat.getDateInstance(Locale.FRANCE);

Format Example

DateFormat.SHORT 4/20/98

DateFormat.MEDIUM 20-Apr-98

DateFormat.LONG April 20, 1998

DateFormat.FULL Monday, April 20, 1998


Date Classes: GregorianCalendarUse GregorianCalendar object to set day

// Example of GregorianCalendar class. This program initializes a// GregorianCalendar object to October 15, 1999, converts the object// to a Date object, then displays the result with DateFormat.

import java.util.GregorianCalendar;import java.util.Calendar;import java.text.DateFormat;import java.util.Date;

class SetDate{ public static void main(String[] args) { // Make a DateFormat object that formats in FULL style DateFormat aDateFormatter = DateFormat.getDateInstance(DateFormat.FULL);

// Initialize aGregCal to October 15, 1999 GregorianCalendar aGregCal = new GregorianCalendar(1999, Calendar.OCTOBER, 15);

// Convert aGregCal to aDate object Date aDate = aGregCal.getTime();

// Display the date with the formatter System.out.println(aDateFormatter.format(aDate)); }}


Date Classes: Discarding ObjectsCreate new GregorianCalendar object, assign to

variableGregorianCalendar someDate = new GregorianCalendar(1999, Calendar.MAY, 12);

Create another object, assign to same variablesomeDate = new GregorianCalendar(1998, Calendar.APRIL, 20);

Garbage collection: Clean up discarded objects

May 12, 1999

someDate

April 20, 1998

May 12, 1999

someDate

This object is nolonger in use


Input StreamsStream is flow of data

Reader at one endWriter at the other end

Stream generalizes input & outputKeyboard electronics different from disk Input stream makes keyboard look like a disk

ReaderWriter Stream


Input Streams: Keyboard ClassHave been using Keyboard class for reading

int num = Keyboard.readInt("Enter number: ");

What's the Keyboardclass hiding?

The System..instream!


Input Streams: System.inSystem.in: the standard input stream

By default, reads characters from the keyboard

Can use System.in many waysDirectly (low-level access)Through layers of abstraction (high-level access)

Program System.in


Input Streams: Read CharactersCan read characters from System.in with read()

// Reads a single character from the keyboard and displays itclass DemonstrateRead{ public static void main(String[] args) throws java.io.IOException { char character;

// Prompt for a character and read it System.out.print("Enter a character: "); System.out.flush(); character = (char) System.in.read(); // Display the character typed System.out.println(); System.out.println("You typed " + character); }}

System.in

'f'

InputStream.read()

'f','i','r','s','t','\n','1','2','3','\n','4','2',' ','5','8','\n', ...


Input Streams: Read CharactersSystem.in.read() returns an integer

Usually cast to charchar character = (char) System.in.read();

System.in.read returns -1 if EOF detectedEOF = end of file (no more characters in stream)

Signaling EOF at keyboardControl-Z (Windows), Control-D (Unix)

Example: Read all characters in stream until EOFint intChar = System.in.read();while (intChar != -1){ // Convert to character char character = (char) intChar; System.out.println("Next character is " + character);

// Get next one intChar = System.in.read();}


Input Streams: Read CharactersExample: Count digits, letters, other characters

Part 1: Setup

// Reads text from the keyboard and displays the// number of digits, upper case letters, lower case letters, // and other characters that the user typed.

class CountCharacters{ public static void main(String[] args) throws java.io.IOException { int nextValue, numUpperCase = 0, numLowerCase = 0, numDigits = 0, numOther = 0; char nextChar;

// Display instructions System.out.println("Enter some text, terminate with EOF");


Input Streams: Read CharactersPart 2: Read and count

// Read from the input stream, count characters until no more // characters in the input stream nextValue = System.in.read(); while (nextValue != -1) { nextChar = (char) nextValue; if (Character.isDigit(nextChar)) { numDigits++; } else if (Character.isUpperCase(nextChar)) { numUpperCase++; } else if (Character.isLowerCase(nextChar)) { numLowerCase++; } else { numOther++; } nextValue = System.in.read(); }


Input Streams: Read CharactersPart 3: Display results

// Display results System.out.println(); System.out.println(); System.out.println("Number of digits: " + numDigits); System.out.println("Number of upper case letters: " + numUpperCase); System.out.println("Number of lower case letters: " + numLowerCase); System.out.println("Number of other characters: " + numOther); }}


Input Streams: Read StringsNo String-reading methods in System.inTo read strings from keyboard

First wrap System.in inside InputStreamReader objectInputStreamReader anInputStreamReader = new InputStreamReader(System.in);

InputStreamReader.read()

an InputStreamReader object

InputStream.read()

'f','i','r','s','t','1','2','3','\n','4','2',' ','5','8','\n', ...

System.in stream

'f'


Input Streams: Read StringsNext, wrap InputStreamReader object in BufferedReader object

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



InputStream.read()

'f','i','r','s','t','\n','1','2','3','\n','4','2',' ','5','8','\n', ...

System.in stream

"first"

BufferedReader.readLine()

a BufferedReader object


Input Streams: Read StringsCan combine these two statements

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

InputStreamReader & BufferedReader in java.io.*Must import java.io.*;

Skeleton for readingimport java.io.*;

class ClassName{ public static void main(String[] args) throws java.io.IOException { // Create a buffered input stream and attach it to standard // input BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in)); ... }}


Input Streams: Read StringsMethods in BufferedReader

read(): Use same as System.in.read() readLine(): Returns complete line typed by user

Example: Read user's name// Reads a user's first name, middle initial,// and last name. Demonstrates use of InputStreamReader, // BufferedReader and the readLine() method.

import java.io.*;

class ReadInputAsString{ public static void main(String[] args) throws java.io.IOException { String firstName, lastName; char middleInitial; // Create an input stream and attach it to the standard // input stream BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in));


Input Streams: Read StringsExample: continued

// Read a line from the user as a String System.out.print("Enter your first name: "); System.out.flush(); firstName = inStream.readLine(); // Read a character from the user System.out.print("Enter your middle initial and last name: "); System.out.flush(); middleInitial = (char) inStream.read();

// Read a line from the user as a String lastName = inStream.readLine();

// Display the strings System.out.println(); System.out.println("Your name is " + firstName + " " + middleInitial + ". " + lastName); }} Enter your first name: Linda

Enter your middle initial and last name: EJones

Your name is Linda E. Jones


Input Streams: Read NumbersTo read a number from

keyboard (int, double, ...) Define a NumberFormat

object Define BufferedReader

object Use BufferedReader object

to Read response as a string Use NumberFormat object

to parse string into Number object

Convert Number object to primitive type



InputStream.read()

'1','2','3','\n','4','2',' ','5','8','\n', ...

System.in stream

"123"



NumberFormatter.parse()

Number(123)

Number.intValue()

123


Input Streams: Read NumbersCode to read a number from keyboard (int, double, ...)

Define a NumberFormat objectNumberFormat aNumberFormatter = NumberFormat.getInstance();

Define BufferedReader object BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in));

Read response as a stringSystem.out.print("Enter an integer: ");System.out.flush();String response = inStream.readLine();

Use NumberFormat object to parse string into Numberobject

Number aNumberObject = aNumberFormatter.parse(response);

Convert Number object to primitive typeint intNumber = aNumberObject.intValue();


Input Streams: Read NumbersCan combine reading, parsing, conversion steps

import java.io.*;import java.text.NumberFormat;

class ReadAnInt2{ public static void main(String[] args) throws java.io.IOException, java.text.ParseException { // Create an input stream and attach it to the standard // input stream BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in));

// Create a number formatter object NumberFormat aNumberFormatter = NumberFormat.getInstance();

// Prompt for input System.out.print("Enter an integer: "); System.out.flush();

// Read the response from the user, convert to Number, // then convert to int int intNumber = aNumberFormatter.parse(inStream.readLine()).intValue();

// Display the value System.out.println("You typed " + intNumber); }}

NoteParseException!


Input Streams: Multiple ValuesTo read several

values on one lineUse

StringTokenizer object

Breaks onestring into parts

Must still convertnumbers (ifnecessary)

"42","58"

StringTokenizer()

StringTokenizer.nextToken()

a StringTokenizer object



InputStream.read()

'4','2',' ','5','8','\n', ...

System.in stream

"42 58"




Input Streams: Multiple ValuesHow to use StringTokenizer

Get string to break apart somehow Initialize object with string to break apart

StringTokenizer tokenizer = new StringTokenizer("42 58");

Use nextToken() method to get partsString token;token = tokenizer.nextToken();System.out.println(token); // Displays 42token = tokenizer.nextToken();System.out.println(token); // Displays 58

Can use hasMoreTokens() method to find last oneStringTokenizer tokenizer = new StringTokenizer("42 58");while (tokenizer.hasMoreTokens()){ System.out.println(tokenizer.nextToken());}


Text FilesText file

File that is human-readable with simple tools (type, more, edit, ...)

Variable-length linesEach line terminated by end-of-line markerExample: Java source file

Easy to read and write text filesUse same classes and methods as

System.in and System.inAdvantage of "streams" approach to I/O


Text Files: The File ClassNeed File object for each file program uses

To defineFile inFile = new File("myFile.dat");

PurposeContains information

about the fileA "placeholder" for

the fileNot the same as

the file data.dat prog.txt input.dat

"myFile.dat"

Computer running program

File variable inFile

Disk of text files


Text Files: The File ClassMethods in the File class

canRead(): Tells if program can read the file canWrite(): Tells if program can write to the filedelete(): Deletes the fileexists(): Tells if the file is there isDirectory(): Tells if the file is really a directory

name isFile(): Tells if the file is a file (not a directory) length(): Tells the length of the file, in bytes


Text Files: The File ClassExample of File class

import java.io.*;

class TellIfExists{ public static void main(String[] args) throws java.io.IOException { File myFile = new File("myFile.dat");

if (myFile.exists()) { System.out.println("myFile.dat exists"); } else { System.out.println("myFile.dat does not exist"); } }}


Text Files: Writing to a FileBefore writing, make sure either

File doesn't exist!outFile.exists()

File exists, and is writeableoutFile.exists() && outFile.canWrite()

Combine conditions!outFile.exists() || outFile.canWrite()

Attach file to a streamFileWriter object: knows how to write stream to a fileWrap FileWriter object in BufferedWriter object for

efficiencyWrap BufferedWriter object in PrintWriter object


Text Files: Writing to a FileExample code

// Initialize the file variableFile outFile = new File("myFile.dat");

// Make sure that the file either doesn't exist or// we can write to itif (!outFile.exists() || outFile.canWrite()){ // Create an output stream and attach it to the file PrintWriter fileOutStream = new PrintWriter(new BufferedWriter( new FileWriter(outFile)));

// Write to the file ...}else{ // Error: Can't write to the file}


Text Files: Writing to a FileUse PrintWriter object like System.out

fileOutStream.print("This goes ");fileOutStream.println("to the file");

System.out and fileOutStream are both output streams•System.out is PrintStream object•fileOutStream is PrintWriter object•PrintStream and PrintWriter are almost identical (PrintWriter is newer)

print(), println(), flush() work the sameOnce done writing to the file, close it

fileOutStream.close();

Program does this when it endGood idea to do explicitly, though


Text Files: Writing to a FileExample

// This program writes a table of squares and// square roots to the file myfile.dat.

import java.io.*;

class WriteSquaresAndSquareRoots{ public static void main(String[] args) throws java.io.IOException { // Initialize the output file variable File outFile = new File("myFile.dat"); if (!outFile.exists() || outFile.canWrite()) { // Create a buffered output stream, wrapped by // PrintWriter, and attach it to the file PrintWriter fileOutStream = new PrintWriter(new BufferedWriter (new FileWriter(outFile)));

// Write the output to the file for (int number = 1; number <= 10; number++) fileOutStream.println(number + "\t" + Math.sqrt(number) + "\t\t" + number * number);


Text Files: Writing to a FileExample (continued)

// Close the output stream fileOutStream.close(); } else { System.out.println("Problem creating output file "); } System.out.println("Done"); }}

Contents of file1 1.0 12 1.4142135623730951 43 1.7320508075688772 94 2.0 165 2.23606797749979 256 2.449489742783178 367 2.6457513110645907 498 2.8284271247461903 649 3.0 8110 3.1622776601683795 100


Text Files: Reading from a FileDefine File object

File inFile = new File("myFile.dat");

Before reading, make sure bothFile exists and is readable

inFile.exists() && inFile.canRead()

Attach file to a streamFileReader object: knows how to read stream from a fileWrap FileReader object in BufferedReader object for

efficiencyBufferedReader works on files just like System.in

read(): read a single character, or -1 if EOF readLine(): read a line, or null if EOF


Text Files: Reading from a FileExample code

// Initialize the file variableFile inFile = new File("myFile.dat");

// Make sure the file can be read fromif (inFile.exists() && inFile.canRead()){ // Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile));

// Read from the file stream the same way as reading // from the keyboard ...}else{ // Error: Can't read from file}


Text Files: Reading from a FileComplete example: read() method

// Reads a file and displays the number of digits,// upper case letters, lower case letters, and other characters// in the file.

import java.io.*;

class CountLettersDigits{ public static void main(String[] args) throws java.io.IOException { int nextValue, numUpperCase = 0, numLowerCase = 0, numDigits = 0, numOther = 0; char nextChar; String inputFileName;

// Create a buffered input stream and attach it to standard // input BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in)); // Get input file name from user System.out.print("Enter input file name: "); System.out.flush(); inputFileName = inStream.readLine();


Text Files: Reading from a FileComplete example (continued)

// Initialize the file variable File inFile = new File(inputFileName);

// Make sure the file can be read from if (inFile.exists() && inFile.canRead()) { // Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile));



// Read from the file nextValue = fileInStream.read(); while (nextValue != -1) { nextChar = (char) nextValue; if (Character.isDigit(nextChar)) { numDigits++; } else if (Character.isUpperCase(nextChar)) { numUpperCase++; } else if (Character.isLowerCase(nextChar)) { numLowerCase++; } else { numOther++; } nextValue = fileInStream.read(); }



// Close the stream fileInStream.close();

// Display results System.out.println("Number of digits: " + numDigits); System.out.println("Number of upper case letters: " + numUpperCase); System.out.println("Number of lower case letters: " + numLowerCase); System.out.println("Number of other characters: " + numOther); } else { System.out.println("Can't read " + inputFileName); } }}

Input file: CountCharacters.javaNumber of digits: 7Number of upper case letters: 96Number of lower case letters: 1001Number of other characters: 832


Text Files: Reading from a FileComplete example: readLine() method

// This program reads a file and displays the file// on the screen, with a line number before each line.

import java.io.*;

class DisplayLinesWithLineNumbers{ public static void main(String[] args) throws java.io.IOException { String inputFileName; String line; int lineNumber = 0;

// Create a buffered input stream and attach it to standard // input BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in)); System.out.println("--- File Lister ---"); System.out.println();



// Get file name from user System.out.print("Enter input file name: "); System.out.flush(); inputFileName = inStream.readLine();

// Initialize the input file variable File inFile = new File(inputFileName); if (inFile.exists() && inFile.canRead()) { // Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile)); System.out.println(); System.out.println("--- Contents of file " + inputFileName + "---");



// Read lines from the input stream, display on screen line = fileInStream.readLine(); while (line != null) { lineNumber++; System.out.println(lineNumber + ":\t" + line); line = fileInStream.readLine(); }

System.out.println("--- End of file ---"); // Close the stream fileInStream.close(); } else { System.out.println("Couldn't open input file " + inputFileName); } }}

--- File Lister ---

Enter input file name: JavaTemplate.java

--- Contents of file JavaTemplate.java---1: class JavaTemplate2: {...--- End of file ---


Text Files: Reading NumbersSame techniques as reading from keyboard

Get string value from a fileUse NumberFormat object to convert to Number objectConvert Number object primitive type

Example// Reads a file of numbers, square roots, and// squares from myfile.dat and displays the contents on the// screen. Each line of the file should have an integer, the// square root of that integer, and the square of that integer.// (Use the program in Listing 6.15 to create the file.)

import java.io.*;import java.util.StringTokenizer;import java.text.NumberFormat;


Text Files: Reading NumbersExample (continued)

class ReadSquaresAndSquareRoots{ public static void main(String[] args) throws java.io.IOException, java.text.ParseException { String line; int number, lineNumber = 0; double squareOfNumber, squareRootOfNumber;

// Create a number formatter object NumberFormat aNumberFormatter = NumberFormat.getInstance();

// Initialize the input file variable File inFile = new File("myfile.dat"); if (inFile.exists() && inFile.canRead()) { // Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile));


Text Files: Reading Numbers Example (continued)

// For each line in the input stream, read an integer and // two doubles (the square of the number and the square // root) and display each value. line = fileInStream.readLine(); while (line != null) { lineNumber++; // Initialize the tokenizer with the last read line StringTokenizer tokenizer = new StringTokenizer(line); // Break the line into an int and two doubles number = aNumberFormatter.parse(tokenizer.nextToken()).intValue(); squareRootOfNumber = aNumberFormatter.parse(tokenizer.nextToken()).doubleValue(); squareOfNumber = aNumberFormatter.parse(tokenizer.nextToken()).doubleValue();

// Dislay the line's contents System.out.println("Line " + lineNumber + " contents:"); System.out.println(" number is " + number); System.out.println(" square root of " + number + " is " + squareRootOfNumber); System.out.println(" square of " + number + " is " + squareOfNumber); // Read the next line line = fileInStream.readLine(); }


Text Files: Reading from a FileExample (continued)

// Close the stream fileInStream.close(); } else { System.out.println("Couldn't open input file"); } }}

Line 1 contents: number is 1 square root of 1 is 1.0 square of 1 is 1.0Line 2 contents: number is 2 square root of 2 is 1.4142135623730951 square of 2 is 4.0Line 3 contents: number is 3 square root of 3 is 1.7320508075688772 square of 3 is 9.0...Line 10 contents: number is 10 square root of 10 is 3.1622776601683795 square of 10 is 100.0


Text Files: Reading from a FileExample: Count characters, lines, words

To count characters: increment for each BufferedRead.read()

To count lines: increment for each '\n'Counting words is trickier

Incremental design and developmentGet easy parts written and tested firstAdd other features one at a time to the working

frameworkAdvantage: bug is most likely in most recently added part

of program


Text Files: Reading from a FileCode for counting characters and lines

// Displays the number of characters and lines in a// text file.

import java.io.*;

class CountCharsLines{ public static void main(String[] args) throws java.io.IOException { String inputFileName; int charCount = 0; int lineCount = 0; int nextValue; char nextChar;

System.out.println("--- Character and line counter ---"); // Create a buffered input stream and attach it to standard // input BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in));


Text Files: Reading from a FileCode for counting characters and lines (continued)

System.out.print("Enter file name: "); System.out.flush(); inputFileName = inStream.readLine(); // Initialize the input file variable File inFile = new File(inputFileName); if (inFile.exists() && inFile.canRead()) { // Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile));

while ((nextValue = fileInStream.read()) != -1) { nextChar = (char) nextValue;

charCount++;

if (nextChar == '\n') { lineCount++; } }


Text Files: Reading from a FileCode for counting characters and lines (continued)


// Display results System.out.println(); System.out.println("Characters in file: " + charCount); System.out.println("Lines in file: " + lineCount); } else { System.out.println("Can't open file" + inputFileName); } }}

--- Character and line counter ---Enter file name: Alice.excerpt.txt

Characters in file: 1127Lines in file: 29


Text Files: Reading from a FileWord counting

"Word": continguous sequence of characters separated by white space

Add word counting: approach 1Count spacesProblem: may be more than one space between words

Add word counting: approach 2Count transitions from non-word to word (word

beginnings)Must keep track of program state: in a word or not


Text Files: Reading from a FileCounting characters, lines, words

// Displays the number of characters, lines, and words// in a text file. (This program extends the character and line// counting program; the changed lines are highlighted.)

import java.io.*;

class CountCharsLinesWords{ public static void main(String[] args) throws java.io.IOException { String inputFileName; int charCount = 0; int lineCount = 0;

int wordCount = 0; int nextValue; char nextChar;

boolean inWord = false;


Text Files: Reading from a FileCounting characters, lines, words (continued)

System.out.println("--- Character, line, and word counter ---"); // Create a buffered input stream and attach it to standard // input BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in)); System.out.print("Enter file name: "); System.out.flush(); inputFileName = inStream.readLine();



// Initialize the input file variable File inFile = new File(inputFileName); if (inFile.exists() && inFile.canRead()) { // Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile));

while ((nextValue = fileInStream.read()) != -1) { nextChar = (char) nextValue;

charCount++;

if (nextChar == '\n') { lineCount++; }

else if (Character.isWhitespace(nextChar)) { inWord = false; } else if (!inWord) { inWord = true; wordCount++; }

}




// Display results System.out.println(); System.out.println("Characters in file: " + charCount); System.out.println("Lines in file: " + lineCount);

System.out.println("Words in file: " + wordCount); } else { System.out.println("Can't open file" + inputFileName); } }}--- Character, line, and word counter ---

Enter file name: Alice.excerpt.txt

Characters in file: 1127Lines in file: 29Words in file: 194


Text Files: Multiple FilesCan read and write multiple files simultaneously

Define separate File object and stream for eachExample: change lower case letters to upper case

Initialize the input file object If it's OK to read from the input file

•Establish an input stream and attach to input file•Initialize the output file object•If the output file doesn't exist or is writeable

•Establish output stream and attach to output file•Process the streams•Close both streams

•Otherwise, display an error message, close input streamOtherwise, display an error message


Text Files: Multiple Files// This program copies an existing file to a new// file, changing all lower case characters to upper case and// leaving other characters as they are.

import java.io.*;

class CopyFileToAllUpperCase{ public static void main(String[] args) throws java.io.IOException { int nextValue; // Create a buffered input stream and attach it to standard // input BufferedReader inStream = new BufferedReader(new InputStreamReader(System.in)); // Display program title System.out.println("--- Copy File to All Upper Case ---"); System.out.println();

// Get file names from user System.out.print("Enter input file name: "); System.out.flush(); String inputFileName = inStream.readLine(); System.out.print("Enter output file name: "); System.out.flush(); String outputFileName = inStream.readLine();


Text Files: Multiple Files // Open the input file File inFile = new File(inputFileName); if (inFile.exists() && inFile.canRead()) { // Create an input stream and attach it to the file BufferedReader fileInStream = new BufferedReader(new FileReader(inFile));

// Open the output file File outFile = new File(outputFileName); if (!outFile.exists() || outFile.canWrite()) { // Create an output stream and attach it to the file PrintWriter fileOutStream = new PrintWriter(new BufferedWriter(new FileWriter(outFile)));

// Read characters from input stream, write each to output // stream until no more characters nextValue = fileInStream.read(); while (nextValue != -1) { fileOutStream.write(Character.toUpperCase((char) nextValue)); nextValue = fileInStream.read(); }

// Close the files fileInStream.close(); fileOutStream.close(); }


Text Files: Multiple Files else { System.out.println("Problem creating output file " + outputFileName); // Close the input file fileInStream.close(); } } else { System.out.println("Couldn't open input file" + inputFileName); } }}

--- Copy File to All Upper Case ---

Enter input file name: Alice.excerpt.txtEnter output file name: Alice.excerpt.new

THERE WAS A TABLE SET OUT UNDER A TREE IN FRONT OF THE HOUSE,AND THE MARCH HARE AND THE HATTER WERE HAVING TEA AT IT: ADORMOUSE WAS SITTING BETWEEN THEM, FAST ASLEEP, AND THE OTHER TWO...

Contents of Alice.excerpt.new, after program finishes:

Displayed on screen:


DatabasesMost computer data stored in databases

Database: collection of information stored in computerDatabase management system (DBMS): set of programs

that maintaina database

Programs must go throughDBMS to get to data

WithoutDBMS

WithDBMS

User

User

OperatingSystem

DataApplication

OperatingSystem

DataApplicationDatabase

ManagementSystem


DatabasesDatabase is more

than just dataDatabase stores

Data Description about

the dataAdvantage

Independence fromprograms

In contrast, Java text file stores just data

Programwith

File Description

OperatingSystem

Filewith

Data only

Programwith

File Description

Programwith

File Description

Program

OperatingSystem

FilewithData

and Description

Program

Program

DatabaseManagement

System

WithoutDBMS

WithDBMS


DatabasesDatabase systems reduce redundancy

Each piece of information stored onceLess chance of inconsistent dataLess work to update the data -- change it onceSaves storage space

Many programs can share the same informationConcurrency control: part of database system that lets

more than one program use same data at onceQuery system lets users get to data

Ordinary users can use -- don't need programmerCan write and execute queries quickly


Convert

Convert

Database Design ProcessStart with idea

Purpose of the databaseConceptual model

High-level design Ignore physical issues Most popular: Entity-

relationship (E/R) modelPhysical model

Low-level design Maps conceptual model to a

database system

Idea

ConceptualModel

PhysicalModel


Database Design: E/R modelEntity-relationship model consists of

Entities: represent real-world objects (people, employees, departments, parts, machines, engines, ...)

Attributes: characteristics of entities (color, weight, size, manager, name, address, part number, ...)

Relationships between entities (employees work for a department, an automobile has an engine, ...)

Entity

Attribute

EntityRelation-ship


Database Design: E/R modelKinds of relationships

1-1: "one-to-one"

1-N: "one-to-many"

N-N: "many-to-many"

Dept ManagerSupervise1 1

Dept EmployeeWorksin

1 N

Student CourseTakesN N


Database Design: E/R modelExample

Department

Worksfor

EmployeeHas

degreeEntity name

Managerof

1

1

1

N

1 N

Name

DeptNumber

Name

EmplNumber

Salary JobCode

Education

Salary JobCode Year

DegreeInstitution


Database ModelsDatabase model: way the database is organizedMajor database models

Hierarchic (old model)Network (old model)Relational (most popular)Object (the future?)

Schema vs. instanceSchema is the layout of the database (like a class in

Java) Instance is the data in the database (like an instance of

an object in Java)


Database Models: HierarchicThe oldest data modelRecord vs. record type

Record types in schema Records in instance

Record type can have any number of children at most one parent

Links by physical pointersWorks well when data

organized in tree-like structure

"Manufacturing"34

1234"Engineering"

341234

"Lee"345630K8A

"Smith"456730K7A

DepartmentName

DeptNumberManager

EmployeeName

EmpNumberSalary

JobCode

EducationInstitution

DegreeYear

"Accounting"34

1234

"Jones"123430K6A

"ABC High"Certif1984

"XYZ College"BS

1990

Schema Instances


Database Models: NetworkGeneralizes the

hierarchic model Data organized as graph Record type can have

more than one parentRecord occurrences

Linked in a "chain"Links by physical pointers

"Manufacturing"34

"Engineering"34

"Lee"345630K8A

"Smith"456730K7A

DepartmentName

DeptNumber

EmployeeName

EmpNumberSalary

JobCodeM

anager of

EducationInstitution

DegreeYear

"Accounting"34

"Jones"123430K6A

"ABC High"Certif1984

"XYZ College"BS

1990

Schema Instances

Works for

Has degree

Worksfor

Hasdegree

Managerof


Database Models: RelationalOrganization by tables

No order to data in tableSchema and instance

Schema is table headings Instance is contents of tables

Links between tables by value Key: identifier attribute for

each row Link by foreign key: key of

another table Physical pointers not used

Department

Name DeptNumber Manager

Accounting 34 1234Engineering 53 3949Manufacturing 21 8493

Employee

Name EmplNumber Salary JobCode DeptNumber

Jones 1234 30K 6A 34Smith 4567 30K 7A 34Lee 3456 30K 8A 34Anders 9876 32K 6B 53Wells 7475 30K 7A 53Mies 3939 29K 8A 21

Education

Institution Degree Year EmplNumber

XYZ College BS 1990 1234ABC High Diploma 1984 1234XYZ College BS 1980 4567GHI University BA 1985 9876PQR Tech Assoc 1994 3939Univ. TUV BS 1985 3456


Database Models: ObjectObject databases are still new

May be the future of all databasesMore likely, relational and object databases will be used

Based on object-oriented programming languages (Smalltalk, Java, C++)

Database structure is the class structure in a languageVery natural way to store data from OO languageEasier to use than translating to another model

Still many problems to be worked outEfficiency, ability to query easily, reliability, ...


Databases: N-N RelationshipsCan implement N-N

relationship directly inObject database

Can't in Hierarchic Network Relational

Must translate in these cases

Student

Course

Takes

NN

Student

Takes

N

Taken by

Student-Course

Course

11

N


Relational Database DesignStart with E/R model

Convert N-N relationships to 2 1-N relationshipsEach entity becomes a relation (table)Each attribute becomes an attribute (column header)For each 1-N relationship

•Put foreign key of "1-side" relation in "N-side" relationFor each 1-1 relationship, either

•Merge the two relations•Treat as 1-N

Next, check the normal form of each relation


Relational Database DesignNormal form

Indicates possible amount of redundant dataHigher normal form is better (less redundancy)

First normal formEach attribute is atomic (can't divide it)

Second normal formKey may be two or more attributesEach attribute must depend fully on the key (not just part

of it)Third normal form

Attributes depend just on the key attribute


Database Query LanguagesQuery language

High-level way to get to the data without programmingAllows users to check the data easily

SQL (structured query language)User interface: textLike a programming language (has syntax)Declarative (state what you want, not how to get it)

QBE (query by example)User interface: graphicalVery easy to use (no syntax, just click and drag)Also declarative


Database Query Languages: SQLQuery 1: list all employees

and their salariesSQL

SELECT Name, SalaryFROM Employee;

Result

Department



Employee



Education



Name Salary

Jones 30K

Smith 30K

Lee 30K

Anders 32K

Wells 30K

Mies 29K


Database Query Languages: SQLQuery 2: list all employees

in dept 34 and their salaries

SQLSELECT Name, SalaryFROM EmployeeWHERE DeptNumber = 34;

Result

Department



Employee



Education



Name Salary

Jones 30K

Smith 30K

Lee 30K


Database Query Languages: SQLQuery 3: list name, dept,

salary of each employeeSQL

SELECT Employee.Name, Salary, Department.NameFROM Employee, DepartmentWHERE Employee.DeptNumber = Department.DeptNumber;

ResultName Salary Name

Jones 30K Accounting

Smith 30K Accounting

Lee 30K Accounting

Anders 32K Engineering

Wells 30K Engineering

Mies 29K Manufacturing

Department



Employee



Education




Database Query Languages: QBEQuery 1: list all employees

and their salariesSolution in Microsoft

Access 97

Department



Employee



Education




Database Query Languages: QBEQuery 2: list all employees in

dept 34 and their salariesSolution in Microsoft Access

97

Department



Employee



Education




Database Query Languages: QBEQuery 3: list name, dept,

salary of each employeeSolution in Microsoft

Access 97

Department



Employee



Education



Documents

Chapter 6 Using Classes: Dates and I/O Streams