1 java b object oriented b powerful b interpreted b portable b platform independent b filename.java...

1

JavaJava

Object OrientedObject Oriented PowerfulPowerful InterpretedInterpreted PortablePortable Platform independentPlatform independent filename.javafilename.java filename.classfilename.class (bytecode)(bytecode)

2

JavaJava

Multi-threadedMulti-threaded Easy to work with multimediaEasy to work with multimedia

• imagesimages• animationanimation• audioaudio• videovideo

Graphics capabilities (and still portable)Graphics capabilities (and still portable) Case sensitiveCase sensitive

3

JavaJava

ApplicationsApplications AppletsApplets

• for the WWWfor the WWW

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ApplicationApplication

//Java application//Java application

public class HelloWorld {public class HelloWorld {

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

{{

System.out.println(“Hello World!…”);System.out.println(“Hello World!…”);

}}

}}

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Public:Public:• If the class is not If the class is not publicpublic, it can be used only by , it can be used only by

other classes in the same other classes in the same packagepackage A A packagepackage is a collection of other packages is a collection of other packages

and classesand classes

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ApplicationsApplications

To display a dialog box containing To display a dialog box containing information use the class information use the class JOptionPaneJOptionPane

Class Class JOptionPaneJOptionPane is defined in the is defined in the package called package called javax.swingjavax.swing

e.g.e.g.

import javax.swing.*;import javax.swing.*;

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import javax.swing.JOptionPane;import javax.swing.JOptionPane;

public class HelloWorld {public class HelloWorld {

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

{{

JOptionPane.showMessageDialog(JOptionPane.showMessageDialog(

null, “Hello\nWorld!…”);null, “Hello\nWorld!…”);

}}

}}

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The The concatination operator “+”concatination operator “+”

int i =5;int i =5;

int j = 6;int j = 6;

JOptionPane.showMessageDialog(JOptionPane.showMessageDialog(

null, “i = ” + i + “j = “ + j);null, “i = ” + i + “j = “ + j);

System.out.println(“x = “ + i + “j = “ + j); System.out.println(“x = “ + i + “j = “ + j);

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Input from keyboardInput from keyboard

int i;int i;

int j;int j;

i = System.in.read();i = System.in.read();

oror

read a string and convert it to an integerread a string and convert it to an integer

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Input from keyboardInput from keyboard

import javax.swing.JOptionPane;import javax.swing.JOptionPane;

public class MyInputpublic class MyInput

{public static void main(String Args[]){{public static void main(String Args[]){

String firstNumber;String firstNumber;

int number1;int number1;

firstNumber = firstNumber = JOptionPane.showInputDialog("Enter an integer: ");JOptionPane.showInputDialog("Enter an integer: ");

number1 = Integer.parseInt(firstNumber);number1 = Integer.parseInt(firstNumber);

System.exit(0);}}System.exit(0);}}

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Primitive data typesPrimitive data types

booleanboolean - 8 bits - true/false - 8 bits - true/false char 16 bits ‘\u0000’ to ‘\uFFFF’ (unicode)char 16 bits ‘\u0000’ to ‘\uFFFF’ (unicode) byte - 8 bitsbyte - 8 bits short - 6 bitsshort - 6 bits int - 32 bitsint - 32 bits long - 64 bitslong - 64 bits float - 32 bitsfloat - 32 bits double - 64 bitsdouble - 64 bits

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OperatorsOperators

Arithmetic operators: +, -, *, /, %Arithmetic operators: +, -, *, /, % Equality and relational operators: ==, !=, >, Equality and relational operators: ==, !=, >,

<, >=, <=<, >=, <= Increment operator: i++, ++iIncrement operator: i++, ++i Decrement operator: i--, --IDecrement operator: i--, --I Assignment operators: =, +=, -=, *=, /=, %=Assignment operators: =, +=, -=, *=, /=, %=

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Control StructuresControl Structures

if(grade >= 16)system.out.println( "passed");

else

system.out.println( "failed");

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switch(grade) {case 'A':

gradeA++;

break;

case 'B': gradeB++;

break;

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case 'C':gradeC++;

break;

case 'D': gradeD++;

break;

default:showStatus("invalid grade. Enter new grade.");

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Repetition StructuresRepetition Structures

Whiledo/while for

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int i = 2;

while(i <=100)

i = i + 1;

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for(int i = 2; i <= 100; i++)

j = j + 1;

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int i = 2;

do { i = i + 1;

} while(i <=100)

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ArraysArrays

Creating an array:

MyObject arrayofobjs[] = new MyObject[10];

add actual MyObject objects to that array:

for (int i=0;

i < arrayofobjs.length; i++) arrayofobjs[i] = new MyObject;

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Creating Arrays - examplesCreating Arrays - examples

String[] stringArray;String[] stringArray;

int[] intArray;int[] intArray;

boolean[] booleanArray;boolean[] booleanArray;

int[] myIntArray = new int[20];int[] myIntArray = new int[20];

int[] numbers = {2, 5, 8, 10};int[] numbers = {2, 5, 8, 10};

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Input/outputInput/output

Files and StreamsFiles and Streams• System.in System.in - - standard input stream objectstandard input stream object• System.out - System.out - standard output stream objectstandard output stream object• System.err - System.err - standard input stream objectstandard input stream object

are three stream object created when a Java are three stream object created when a Java program is executed.program is executed.

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To perform file processing in JavaTo perform file processing in Java

java.iojava.io

package must be imported.package must be imported. Stream ClassesStream Classes

• FileInputStreamFileInputStream - for input from a file - for input from a file

• FileOutputStreamFileOutputStream - for output to a file- for output to a file

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Object

InputStream OutputStream

FileInputStream FileOutputStream

PipedInputStream PipedOutputStream

Class Hierarchy

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More on Class HierarchyMore on Class Hierarchy

ObjectObject• FileFile• FileDescriptorFileDescriptor• StreamTokenizerStreamTokenizer• InputStreamInputStream• OutputStreamOutputStream• RandomAccessFileRandomAccessFile

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InputStreamInputStream• ByteArrayInputStreamByteArrayInputStream• SequenceInputStreamSequenceInputStream• StringBufferInputStreamStringBufferInputStream• PipedInputStreamPipedInputStream• FileInputStreamFileInputStream• FilterInputStreamFilterInputStream

– DataInputStreamDataInputStream– BufferedInputStreamBufferedInputStream– PushBackInputStreamPushBackInputStream– LineNumberInputStreamLineNumberInputStream

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OutputStreamOutputStream• ByteArrayOutputStreamByteArrayOutputStream• PipedOutputStreamPipedOutputStream• FileOutputStreamFileOutputStream• FilterOutputStreamFilterOutputStream

– DataOutputStreamDataOutputStream– BufferedOutputStreamBufferedOutputStream– PrintStreamPrintStream

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PipesPipes• synchronised communication synchronised communication

channels between threadschannels between threads• One thread send data to another by One thread send data to another by

writing to a writing to a PipedOutputStream.PipedOutputStream.• The target thread reads information The target thread reads information

from the pipe via a from the pipe via a PipedInputStreamPipedInputStream

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Creating a FileOutputStream Creating a FileOutputStream object and attempting to open a object and attempting to open a file:file:

try {try {

output = new DataOutputStream(output = new DataOutputStream(

new FileOutputStream(“afile.dat”));new FileOutputStream(“afile.dat”));

}}

catch ( IOException e ) {catch ( IOException e ) {

System.err.println(“File not opened System.err.println(“File not opened properly\n” + e.toString());properly\n” + e.toString());

System.exit( 1 );}System.exit( 1 );}

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Writing to a fileWriting to a file

output.writeInt ( accountNumber);output.writeInt ( accountNumber);

output.writeDouble(doubleValue);output.writeDouble(doubleValue); Closing the fileClosing the file

output.close();output.close();

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Opening a file to readOpening a file to read

try {try {

input = new DataInputStream(input = new DataInputStream(

new FileInputStream(“afile.dat”));new FileInputStream(“afile.dat”));

}}

catch ( IOException e ) {catch ( IOException e ) {

System.err.println(“File not opened System.err.println(“File not opened properly\n” + e.toString());properly\n” + e.toString());

System.exit( 1 );}System.exit( 1 );}

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Reading from a fileReading from a file

Account = input.readInt();Account = input.readInt();

balance = input.readDouble();balance = input.readDouble();

input.close();input.close();

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Read/WriteRead/Write

And of courseAnd of course

System.out.print(“Enter grade:”);System.out.print(“Enter grade:”);

grade = System.in.read();grade = System.in.read();

1 java b object oriented b powerful b interpreted b portable b platform independent b filename.java...

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