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United International University

Trimester: Fall 2009

Course: CSI 211

Course Title: Object Oriented Programming

Lecture 1a: Java Introduction

What is Java?

A Language

A Platform

An OS

A Chip

Java - Characteristics

Uses C/C++ basic syntax and basic data types -int, char, float, double, long,

short, byte etc.

Uses standard C/C++ control structures

Pure OO language

No stand alone functions -All code is part of a class

No explicit pointers - uses references

Uses garbage collection

Java is strongly typed

Java More characteristics

Java is normally compiled to a bytecode ;Java bytecode is a machine language

for an abstract machine

Each platform (or browser) that runs Java has a Java Virtual Machine (JVM or

sometimes VM) . The JVM executes Java bytecodes

JVMs with Just-In-Time (JIT) compilers will:

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Compile the bytecodes to native machine code

This is done for each method the first time is executed

The native machine code is cached

The JVM then runs the native machine code for the method

Java 1.2 will have a JVM (Hotspot) that runs Java code much faster than

simple JIT JVMs

Other languages can be compiled to Java's bytecode

An Ada compiler exists that compiles Ada to Java bytecode

Java - The Platform

Java has a large API (application programming interface) covering a wide

range of areas The following list of Java APIs and applications from Sun

show the range of applications of Java . For reference

http://java.sun.com/products/index.html

Java Foundation Classes (JFC) - GUI

Java Interface Definition Language (IDL) - CORBA

JDBCTM Database Access

JavaBeansTM - componentware

JavaTM Communications API - serial & parallel port

JavaHelpTM

JavaTM Advanced Imaging

JavaTM Web Server TM

PersonalJavaTM - Java on personal consumer devices

EmbeddedJavaTM - Java on embedded devices

JavaTM Card TM - Java on a smart card

JavaTM Naming and Directory Interface TM (JNDI)

Java Message Service (JMS)

http://java.sun.com/products/index.htmlhttp://java.sun.com/products/index.html

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Java - The OS

Sun and IBM are implementing the Java OS which is an operating system that executesthe Java environment directly on hardware platforms

Java - The Chip

Some companies are implementing hardware that uses the Java bytecode as nativemachine code

Versions of Java

JDK(Java Development Kit) 1.0.2o First widely used version

o All browsers with Java support this version

JDK 1.1.X

Current release is JDK 1.1.6o Made changes to the language from JDK 1.0.X

o Add inner classes , Generics

o API is about 3 times larger than 1.0.2

o Event model for GUI components changed from 1.0.2

JDK 1.2 -Currently in beta 4o API is about 3 times larger than 1.1.X, so lots of new stuff

o Should contain major performance increases

o Major additions to GUI components

JAVA IDE

Using JDK you can compile and run java program from command line.o c:> javac HelloWorld. java - compiling here and it will produce

HelloWorld.class i.e. bytecode.o c:>java HelloWorld - It runs java byte code on native machine

Creating, Compiling, Debugging and Execution for these four steps JDK is notuser friendly. IDE is provided for that. A list of IDEs are:

o Eclipse - from IBM

o Netbeans


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o Jbuilder from Borland

o Visual Studio J++ - from microsoft

o Visual Cafe from Webgain.


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o

An Example HelloWorld

/**

This is my first java program*/

public class HelloWorldExample

{

public static void main( String args[] )

{

System.out.println("Hello World");

}

}

Java Source Code Naming Conventions

All java source file should end in .java

Each .java file can contain only one public class

The name of the file should be the name of the public class plus ".java"

Do not use abbreviations in the name of the class

If the class name contains multiple words then capitalize the first letter of each

word ex. HelloWorld.java

CLASSPATH

Java uses the environment variable CLASSPATHto locate class libraries

.class files those needed to compile or run the program it searches from

CLASSPATH

By default class path consists only the current directory but you can provide them

inclasspath option ofjavac or include directories in CLASSPATHenvironmentvariables.

Example classpath = . ; c:\java\lib; c:\csi211\lab


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Some Basic Java Syntax

Java Comments

/* Standard C comment works*/

// C++ comment works

/** Special comment for documentation java comments*/

class Syntax

{


{

int aVariable = 5;double aFloat = 5.8;

if ( aVariable < aFloat )

System.out.println( "True" );

int b = 10; // This is legal in Java

char c;

c = 'a';

}

}

Java Program Style and Layout

Three different indentation styles you can use

You can pick a reasonable indentation style and use it consistently in your

programs

Style#1

class Syntax { // brace starts from here

public static void main( String args[] ) {

int aVariable = 5;


System.out.println( "True" );}

}


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Style #2

class Syntax

{ // brace starts


{

int aVariable = 5;



}

}

Style#3

class Syntax

{// brace starts


{

int aVariable = 5;

if ( aVariable < aFloat )System.out.println( "True" );

}

}

Naming conventions

Class Naming UsesCapitalized word(s) i.e. Title case

Examples:-

HelloWorld, MyList, StudentMark

Wrong:helloWorld, HW (do not use abbreviation)

Variable and function names

starts with a lowercase letter and after that use Title case

Examples:-

variableAndFunctionNames

aFloat, studentName

Names of constants

All are capital letters and separated by underscore. Example isNAMES_OF_CONSTANTS


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Example of Keywords - do not use for any naming

abstract default implements protected throws

boolean do import public transient

break double instanceof return try

byte else int short void

case extends interface static volatile

catch final long super while

char finally native switch

class float new synchronized

const for package this

continue if private throw

Reserved for possible future use (not used now)

byvalue cast future generic goto

inner operator outer rest var

Boolean

true, false act like keywords but are boolean constants

publicclass BooleanTest {

publicstaticvoid main( String args[] ){

boolean flag = 2 > 3;

if ( flag && true)


else

System.out.println( "False" );

}

}

Input and Output

Standard Java Output

System.out is standard out in Java

System.err is error out in Java


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class Output

{


{

// Standard out

System.out.print( "Prints, but no newline" );

System.out.println( "Prints, adds platforms newline at end" );

double test = 4.6;

System.out.println( test );

System.out.println( "You can use " + "the plus operator on "

+ test + " String mixed with numbers" );

System.out.println( 5 + "\t" + 7 );

System.out.println( "trouble" + 5 + 7 ); //Problem here

System.out.println( "ok" + (5 + 7) );

System.out.flush(); // flushes output buffer

System.err.println( "Standard error output" );

}

}

Output

Prints, but no linefeed Prints, adds linefeed at end

4.6

You can use the plus operator on 4.6 String mixed with numbers

5 7

trouble57

ok12

Standard error output

Standard Java Input

Java assumes that you will be using a GUI for input from the user Hence there is

no "simple" way to read input from a user Scanner class is in jdk 1.5

package lecture01;

import java.util.Scanner;

publicclass TestInput {

publicstaticvoid main( String[] args ){

Scanner scanner = new Scanner(System.in);

System.out.print("Write your name: ");

String userName = scanner.nextLine();

System.out.println("Your name is : " + userName);

}

}

OutputWrite your name: Monzurur Rahman

Your name is : Monzurur RahmanYou typed: 34


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Basic Data Types

class PrimitiveTypes

{

public static void main( String args[] ){

// Integral Types

byte aByteVariable; // 8-bits

short aShortVariable; // 16-bits

int aIntVariable; // 32-bits

long aLongVariable; // 64-bits

// Floating-Point Types

float aFloatVariable; // 32-bit IEEE 754 float

double aDoubleVariable; // 64-bit IEEE 754 float

// Character Type

char aCharVariable; // always 16-bit Unicode

// Boolean Types

boolean aBooleanVariable; // true or false

}}

Arithmetic Literals

class ArithmeticLiterals

{


{

long aLong = 5L;

long anotherLong = 12l;

int aHex = 0x1;int alsoHex = 0X1aF;

int anOctal = 01;

int anotherOctal = 0731;

long aLongOctal = 012L;

long aLongHex = 0xAL;

float aFloat = 5.40F;

float alsoAFloat = 5.40f;

float anotherFloat = 5.40e2f;

float yetAnotherFloat = 5.40e+12f;

float compileError = 5.40; //Need cast here

double aDouble = 5.40; //Double is default!!

double alsoADouble = 5.40d;

double moreDouble = 5.40D;double anotherDouble = 5.40e2;

double yetAnotherDouble = 5.40e+12d;

}

}


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Operations on Primitive Types

Integer Type

Equality = !=Relational < >=

Unary + -

Arithmetic + - * / %

Pre, postfix increment/decrement ++ --

Shift > >>>

Unary Bitwise logical negation ~

Binary Bitwise logical operators & | ^

class Operations{


{

int a = 2;

int b = +4;

int c = a + b;

if ( b > a )

System.out.println("b is larger");

else

System.out.println("a is larger");

System.out.println( a > 1); // Shift right: 1

System.out.println( ~a ); // bitwise negation: -3System.out.println( a | b); // bitwise OR: 6

System.out.println( a ^ b); // bitwise XOR: 6

System.out.println( a & b); // bitwise AND: 0

}

}

Floating-Point Types Operations

Equality = !=

Relational < >=

Unary + -

Arithmetic + - * / %

Pre, postfix increment/decrement ++ --


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N aN, +, -

Zero divide with floating-point results in +, -

Overflow results in either +, -.

Underflow results in zero.

An operation that has no mathematically definite result produces NaN - Not aNumber

NaN is not equal to any number, including another NaN

class NaN

{


{

float size = 0;float average = 10 / size;

float infinity = 1.40e38f * 1.40e38f;

System.out.println( average ); // Prints Infinity

System.out.println( infinity ); // Prints Infinity

}

}

Casting

class Casting

{


{

int anInt = 5;

float aFloat = 5.8f;

aFloat = anInt; // Implicit casts up are ok

anInt = aFloat ; // Compile error,

// must explicitly cast down

anInt = (int) aFloat ;

float error = 5.8; // Compile error, 5.8 is double

float works = ( float) 5.8;

char c = (char) aFloat;

double aDouble = 12D;

double bDouble = anInt + aDouble; // anInt is cast upto double,

int noWay = 5 / 0; // Compile error, compiler detects

// zero divide

int zero = 0;

int trouble = 5 / zero; //Some compilers may give error here

int notZeroYet;


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notZeroYet = 0;

trouble = 5 / notZeroYet ; // No compile error!

}

}

Ints and Booleans are Differentclass UseBoolean

{


{

if ( ( 5 > 4 ) == true )

System.out.println( "Java's explicit compare " );

if ( 5 > 4 )

System.out.println( "Java's implicit compare " );

if ( ( 5 > 4 ) != 0 ) // Compile error

System.out.println( "C way does not work" );

boolean cantCastFromIntToBoolean = (boolean) 0;

// compile error

int x = 10;int y = 5;

if ( x = y ) // Compile error

System.out.println( "This does not work in Java " );

}

}

Default Values of Variables

All arithmetic variables (int, float, double) are initialize to 0

char variables are initialize to the null character: '\u000'

boolean variables are initialize to false

reference variables are initialize to null

Compiler usually complains about using variables before explicitly giving them a value

class InitializeBeforeUsing

{


{

int noExplicitValue;

System.out.println( noExplicitValue ); // Compile error

int someValue;

boolean tautology = true;if ( tautology )

{

someValue = 5;

}

System.out.println( someValue ); // Compile error

}

}


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Characters

class CharactersLiterals

{


{char backspace = '\b';

char tab = '\t';

char linefeed = '\n';

char formFeed = '\f';

char carriageReturn = '\r';

char doubleQuote = '\"';

char singleQuote = '\'';

char aCharacter = 'b';

char unicodeFormat = '\u0062'; // 'b'

}

}

Unicode

Superset of ASCII

Includes:

ASCII, Latin letter with diacritics

Greek, Cyrillic

Korean HangulHan ( Chinese, Japanese, Korean )

*************** End of Lecture 1a **************


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CSI-211-W01a