Chapt. 1

Introduction to Core Java

Lecture 1: Overview of Java

Introduction

Java is a programming language invented by James Gosling and others in 1994.

originally named Oak ,was developed as a part of the Green project at the Sun Company.

A general-purpose object-oriented language

Based on C/C++.

Designed for easy Web/Internet applications.

Widespread acceptance.

Java FeaturesJava is simple

Java is object-oriented

Java is distributed

Java is interpreted

Java is robust

Java is secure

Java is architecture-neutral

Java is portable

High performance

Java is multithreaded

Java is dynamic

Java Features Simple

fixes some clumsy features of C++ no pointers automatic garbage collection rich pre-defined class library http://java.sun.com/j2se/1.4.2/docs/api/

Object oriented focus on the data (objects) and methods manipulating the data all functions are associated with objects almost all datatypes are objects (files, strings, etc.) potentially better code organization and reuse

Complied and Interpreted java compiler generate byte-codes, not native machine code the compiled byte-codes are platform-independent java bytecodes are translated on the fly to machine readable

instructions in runtime (Java Virtual Machine)

Platform Independent and Portable same application runs on all platforms the sizes of the primitive data types are always the same the libraries define portable interfaces .

Java Features

OS/Hardware

machine codeC source code

myprog.cgcc

myprog.exe

Platform Dependent

JVM

bytecodeJava source code

myprog.javajavac

myprog.class

OS/Hardware

Platform Independent

Java Features

Reliable (Robust) extensive compile-time and runtime error checking. no pointers but real arrays. Memory corruptions or unauthorized

memory accesses are impossible. automatic garbage collection tracks objects usage over time.

Secure usage in networked environments requires more security. memory allocation model is a major defense. access restrictions are forced (private, public).

Java Features

Multithreaded and Interactive multiple concurrent threads of executions can run

simultaneously utilizes a sophisticated set of synchronization primitives (based

on monitors and condition variables paradigm) to achieve this . Hence improves the interactive performance of graphics

application.

Dynamic and Extensible java is designed to adapt to evolving environment. libraries can freely add new methods and instance variables

without any effect on their clients. interfaces promote flexibility and reusability in code by specifying

a set of methods an object can perform, but leaves open how these methods should be implemented.

Java Features (4)Dynamic and Extensible

Functions written in other languages can be accessed in java program can check the class type in runtime

Distributed Designed for creating applications on networks. Can access remote object on Internet as easily as they can do in a local system. Hence enables multiple programmer at multiple remote places can work on single project together.

High Performanceo Java performance is impressive due to use of byte code and multithreading.

Java Features

Architecture-Neutralo Write once, run anywhere any time, forever.

JDK Environment & toolsJDK comes with a collection of tools that are used for

developing and running java programs.

Sr. No Tool Description

1 Applet viewer Enables to run Java applets.

2 Java Java Interpreter runs application programs and applet by reading bytecode.

3 Javac Java complier translate source code to byte code.

4 Javadoc Creates HTML documents from Java source code files.

5 Javah Produces header files for use with native methods

6 javap Java disassembler convert bytecode files into program description

7 jdb Java debugger which helps us to find errors in our programs

Application Program InterfaceJava Standard library (API) includes hundreds of classes

methods grouped into several packages.Sr.No

Package Description

1 Language Support Package

Required for implementing basic features of java.

2 Utilities Package Provides utility functions such as date and time functions.

3 Input/output Package Required for input/output manipulation.

4 Networking Package Enables to communicate with other computers via Internet.

5 AWT Package The abstract Window Toolkit package contains classes that implements platform-independent GUI.

6 Applet Package Includes set of classes that allows us to create Java applets.

Object Oriented Concepts with respect to javaClass

A blueprint that defines the attributes and methods

ObjectAn instance of a Class

AbstractionHide certain details and show only essential details

EncapsulationBinding data and methods together

InheritanceInherit the features of the superclass

PolymorphismOne name having many forms

Difference between c++ & java

Java is truly object oriented.Java does not support operater overloading.Java does not have template classes as in c++Java does not support multiple inheritance of

classes. But can be achieved by using interface.Java does not support global variables. Every

variable and method is declared within a class and forms part of that class.

Java does not use pointer.

Difference between c++ & java

Java has relacesd destructor function with finalize() function.

There are no header files in java.

Appendix A: Introduction to Java 17

how Java Works?

Install JavaTM 2 Platform on your machine

Can be installed on different platforms: Unix/Linux Windows Mac OS

Follow the on-line instructions:http://java.sun.com/docs/books/tutorial/getStarted/cupojava/index.html

Getting Started:

(1) Create the source file: open a text editor, type in the code which defines a class

(HelloWorldApp) and then save it in a file (HelloWorldApp.java) file and class name are case sensitive and must be matched

exactly (except the .java part)

Example Code: HelloWorldApp.java

/** * The HelloWorldApp class implements an application * that displays "Hello World!" to the standard output */ class HelloWorldApp {

public static void main(String[] args) { // Display "Hello World!" System.out.println("Hello World!");

} }

Java is CASE SENSITIVE!

Getting Started:

(2) Compile the program: compile HelloWorldApp.java by using the following command:

javac HelloWorldApp.java

it generates a file named HelloWorldApp.class

‘javac’ is not recognized as an internal or external command, operable program or hatch file.

javac: Command not found

if you see one of these errors, you have two choices:1) specify the full path in which the javac program locates every time. For example:

C:\j2sdk1.4.2_09\bin\javac HelloWorldApp.java

2) set the PATH environment variable

Getting Started:

(3) Run the program: run the code through:

java HelloWorldApp

Note that the command is java, not javac, and you refer to

HelloWorldApp, not HelloWorldApp.java or HelloWorldApp.class

Exception in thread "main" java.lang.NoClassDefFoundError:

HelloWorldApp

if you see this error, you may need to set the environment variable

CLASSPATH.

Java Programming Fundamentals

Structure of Java ProgramData TypesVariablesOperatorsKeywords

General Structure of Program

Documentation Section

Package Statement

Import Statement

Main Method Class {

Main Method definition }

Interface Statement

Class Definition

suggested

Optional

Optional

Optional

Optional

Essential

Java Tokens

Smallest Individual unit in Java Program is called as Java Tokens

Java includes five types of tokenso Reserved Keywords.o Identifierso Literals o Operatorso Separators

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Java Keywords

abstract boolean break byte case catch char

class const continue default do double else

extends final finally float for goto if

implements import instanceof int interface long native

new package private protected public return short

static strictfp super switch synchronized

this throw

throws transient try void volatile while assert

Variables

Variables:NameTypeValue

Naming:May contain numbers, underscore, dollar sign, or

lettersCan not start with numberCan be any lengthReserved keywordsCase sensitive

Data Types

Primitive(built-in)Non Primitive(Derived)

ArraysClassesInterface

Primitive data typesData Types Bit Min Value Max Value

Byte 8 -27 or (-128) 27-1 0r(127)

Short 16 -215 or(-32768) 215-1 or(32767)

Int 32 -231 231-1

Long 64 -231 231-1

Float 32 3.4e-038 3.4e+038

Double 64 1.7e-308 1.7e+308

Boolean 1 true false

Char 16

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Definition: An operator performs a particular operation on the operands it is applied on

Types of operatorsAssignment OperatorsArithmetic OperatorsUnary OperatorsEquality OperatorsRelational OperatorsConditional Operatorsinstaceof OperatorBitwise OperatorsShift Operators

Operators - Types

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Assignment Operator

Arithmetic Operators

Operator Description Example

= Assignment int i = 10;int j = i;

Operators – Assignment Operators/Arithmetic Operators

Operator Description Example

+ Addition int i = 8 + 9; byte b = (byte) 5+4;

- Subtraction int i = 9 – 4;

* Multiplication int i = 8 * 6;

/ Division int i = 10 / 2;

% Remainder int i = 10 % 3;

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Unary Operators

Operator Description Example

+ Unary plus int i = +1;

- Unary minus int i = -1;

++ Increment int j = i++;

-- Decrement int j = i--;

! Logical Not boolean j = !true;

Operators – Unary Operators/Equality Operators

Operator Description Example

== Equality If (i==1)

!= Non equality If (i != 4)

• Equality Operators

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Relational Operators

Operator Description Example

> Greater than if ( x > 4)

< Less than if ( x < 4)

>= Greater than or equal to if ( x >= 4)

<= Less than or equal to if ( x <= 4)

Operators – Relational Operators/Conditional Operators

Operator Description Example

&& Conditional and If (a == 4 && b == 5)

|| Conditional or If (a == 4 || b == 5)

• Conditional Operators

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instanceof Operator

Operator Description Example

instanceof

Instamce of If (john instanceof person)

Operators – instanceof Operator/Bitwise Operators/shift operators

Operator Description Example

& Bitwise and 001 & 111 = 1

| Bitwise or 001 | 110 = 111

^ Bitwise ex-or 001 ^ 110 = 111

~ Reverse ~011 = -10

• Bitwise Operators

• Shift Operators

Operator Description Example

>> Right shift 4 >> 1 = 100 >> 1 = 010 = 2

<< Left Shift 4 << 1 = 100 << 1 = 1000 = 8

>>> Unsigned Right shift

4 >>> 1 = 100 >>> 1 = 010 = 2

Increment Operator: ++

m++; ++m Decrement operator:--

m--;--mConditional Operator

exp?exp2:exp3Dot Operator

person. age, person. Salary();

Operators – Increment Operators/Decrement Operators /Conditional Operators

Java Expression

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Flow Control – if-else if-else

if-else

Syntax Example

if (<condition-1>) { // logic for true condition-1 goes here} else if (<condition-2>) { // logic for true condition-2 goes here} else { // if no condition is met, control comes here}

int a = 10;if (a < 10 ) { System.out.println(“Less than 10”);} else if (a > 10) { System.out.pritln(“Greater than 10”);} else { System.out.println(“Equal to 10”);}

Result: Equal to 10s

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Flow Control – switch

Syntax Example

switch (<value>) { case <a>: // stmt-1 break; case <b>: //stmt-2 break; default:

//stmt-3

int a = 10;switch (a) { case 1: System.out.println(“1”); break; case 10: System.out.println(“10”); break; default: System.out.println(“None”);

Result: 10

• switch

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Flow Control – do-while / while

do-while

Syntax Example

do { // stmt-1} while (<condition>);

int i = 0;do {System.out.println(“In do”); i++;} while ( i < 10);

Result: Prints “In do” 11 times

• whileSyntax Example

while (<condition>) {//stmt

}

int i = 0;while ( i < 10 ) { System.out.println(“In while”); i++;}

Result: “In while” 10 times

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Flow Control – for loop

for

Syntax Example

for ( initialize; condition; expression){ // stmt}

for (int i = 0; i < 10; i++){ System.out.println(“In for”);}

Result: Prints “In do” 10 times