1.Java Basics

8/8/2019 1.Java Basics

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JAVA BASICS


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What is Java?

Java is ahigh-level,third generationprogramming language,like C, Fortranandcan be used to write computer applications

that crunchnumbers, process words, playgames, store data or do any ofthethousandsof other things computer software can do.

Javatechnology is botha programminglanguageand a platform.


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JAVA PLATFORM

Aplatform is thehardware or software

environment in whicha program runs.

The Java platformhas two components:TheJava Virtual Machine

TheJava Application Programming Interface (API)


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JAVA BUZZ WORDS

OBJECT ORIENTED

PLATFORM INDEPENDENT

SIMPLE

SECURE

SUITABLE FOR WEB APPLICATION

ROBUST

PORTABLE

EXCEPTION HANDLING

MULTI THREADING BUILT IN API

OPEN SOURCE


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OBJECT ORIENTED PROGRAMMING

In object-oriented programs data is represented by

objects. Objects havetwo sections

Fields (Instancevariables) tellyou whatan

object is.

Methods tellyou whatan object does.

These fields and methods are closelytied to the

object's real world characteristics and behavior.


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OOP Principles

ENCAPSULATION

Binding ofattributes and behaviour insidea class

INHERITANCE

Deriving the properties of one class bythe other

POLYMORPHISM

Using the samename for differenttypes of

actions


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PLATFORM INDEPENDENT

Java is compiled to an intermediate form

called byte-code,a specialnative program

called the Java interpreter reads the byte code

and executes the corresponding native

machine instructions.


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COMPILATION

.JAVA FILE JAVAC.EXE .CLASS FILE

EXECUTION

.CLASS FILE JAVA.EXE .EXE FILE

SOURCE CODE BYTE CODECOMPILER

MACINE CODEINTERPRETERBYTE CODE


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Portability

Three features makeJava programs portable:

1. The language. TheJava language is completely

specified; all data-type sizes and formats are definedas part ofthelanguage.

2. The library. TheJava class library is available witha

Java runtime system, becausea portable program isofno use ifyou cannot usethe same class library on

every platform.


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3. The byte code. TheJava runtime system does

not compileyour source codeirectly into

machinelanguage Instead,Java programs aretranslated into machine-independent byte

code. The byte code is easily interpreted and

therefore can beexecuted onany platform

having aJava runtime system.

Portability


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Security

Therearetwo mainlines of defense: Interpreter level:

No pointer arithmetic

Garbage collection

Array bounds checking No illegal data conversions

Browser level (applies to applets only):

No local file I/O

Sockets back to host only

No calls to nativemethods


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Robustness

TheJava language is robust. Ithas severalfeatures designed to avoid crashes

during programexecution, including:

No pointer arithmetic Garbage collection--no bad addresses

Arrayand string bounds checking

No jumping to bad method addresses

Interfaces and exceptions


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EXCEPTIONS HANDLING

Java is having a specialtype ofexceptionhandling

mechanism whichallows theexecution ofthe

programevenafter getting a runtime bug.

It is handled by using a set of classes & keywords like

try

catch

finally

throw

throws


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JAVA IS MULTITHREADED

A single Java program canhavemany

differentthreads executing independently

and continuously.

This makes Javavery responsiveto user input.

For this it uses a built in features like Thread class

Runnable interface


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BUILT IN API

Javahas a rich set of collection of built in APIs,

which facilitates the programmer withmuch

ofthe programming aspects. Like,

java.lang

java.io

java.util

java.netand so on.,


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Coding Hello World Application

class HelloWorld

{

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

}


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SAVING

We can savea javaapplication by

Taking the class name whichhas themain()

Taking the class or interface declared as public

Tip:

enclosethe filename in double quotes as Notepadadd athreeletter ".txt" extensionto allthe filesthey save withouttelling you. Thus you can

unexpectedlyend up witha file called"HelloWorld.java.txt."


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Compilation & Execution

Under Windows, it's similar. You just do this ina DOS

shell.

C:> javac HelloWorld.java

C:> java HelloWorld

Hello World

C:>

Noticethatyou usethe .javaextension whencompiling a file, butyou do not usethe .class

extension when running a file.


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JAVA BUILDING BLOCKS


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JAVA TOKENS

WHITE SPACE

COMMENTS

IDENTIFIERS

LITERALS SEPERATORS

OPERATORS

DATA TYPES

CONTROL STATEMENT

ARRAYS

CLASSES, OBJECTS, METHODS

KEYWORDS


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WHITE SPACE

Blank space introduced for proper functioning

ofa program

Java is a free formlanguage whichnever caresabout white spaces


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COMMENTS

Its anonexecutable statement provided to

geta brief ideaaboutthemodules of

applications

Types:

Singleline://comment

Multi line:/*......comment..*/

Documentation:/**comment*/


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IDENTIFIERS

Group of uppercase,lowercase characters,

numbers,and some special characters

Rules: No special characters other than _ and $

It should not start withnumbers

No space in between


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LITERALS

We can createaliteral ofa datatype by creating

the constant representation of it.

Char

a Numbers 100

Float 10.09f

Double 10.09 Boolean true, false


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SEPERATORS

{} Braces

() Parenthesis

[] Brackets ; Semi colon

, Comma

. Access operator


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OPERATORS

Arithmetic

Bitwise

Logical Relational


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DATA TYPESTYPE KEYWORD SIZE

CHARACTER char 16

NUMBERS byte

short

int

long

8

16

32

64

FLOATING Pt float

double

3264

BOOLEAN boolean 1


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CONTROL STATEMENTS

Selection

if, switch

Iteration while, do-while, for

Jump

break, continue, return

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