03 Java - LN01startingpoint

8/18/2019 03 Java - LN01startingpoint

1/29

Object Orientated Programming

An Introduction to Java


2/29

• For the most accurate and up-to-date

tutorials, please access the latest version

from Suns official !ebsite for the Java S"

#utorials $%ast &pdated '()*()++', !hich

can be found at http((java.sun.com

(docs(boo/s(tutorial.

http://java.sun.com/docs/books/tutorial/information/history.htmlhttp://java.sun.com/docs/books/tutorial/http://java.sun.com/docs/books/tutorial/http://java.sun.com/docs/books/tutorial/http://java.sun.com/docs/books/tutorial/http://java.sun.com/docs/books/tutorial/http://java.sun.com/docs/books/tutorial/information/history.html


3/29

Features of OOP

• 0lasses

• Objects

• Instantiation• Inheritance

• 1embership Functions


4/29

1ore OOP Features

• 2ata "ncapsulation

• Pol3morphism

• Operator Overloading• 1essage Passing

• Soft!are 4e-&se


5/29

5istor3 of Java

• Java

• Java, first released by Sun Microsystems in 1994

– Originally for intelligent consumer-electronic devices

– Ten used for creating !eb "ages #it dynamic content

– $o# also used for%

• &evelo" large-scale enter"rise a""lications

• 'nance !!! server functionality

• (rovide a""lications for consumer devices )cell "ones, etc*+


6/29

#he "mergence of Java

• In the past decade Java has emerged in !ide

use partiall3 because of its similarit3 to 0 and to

066

• Perhaps more important is its implementationusing a virtual machine that is intended to run

code unchanged on man3 different platforms.

• #his last feature has made it ver3 attractive to

larger development shops !ith heterogeneous

environments.


7/29

7e3 8enefits of Java

• Java is #rite once, run any#ere

– arcitecture neutral – "ortable across different "latforms

– &ue to Java .irtual Macine )J.M+

• Security features

– igly configurable security levels "revent any "iece of Java code doing armto te ost system

• $et#or/-centric "latform

– easy to #or/ #it resources across a net#or/ and to create net#or/ baseda""lications

• Ob0ect Oriented

– an interacting collection of inde"endent soft#are com"onents

– dynamic etensible "rograms


8/29

7e3 8enefits of Java

• Internationalisation 9 uses :; bit &nicode characters that represents the phonetic

and ideographic character sets of the entire !orld

• Performance

9 although an interpreted language Java programs run almostas fast as native 0, 066 programs

• Simple and eas3 to develop

9 po!erful < !ell designed set of APIs


9/29

Java 0lass %ibraries

• 0lasses

9 Include methods that perform tas/s

• 4eturn information after tas/ completion

9 &sed to build Java programs

• Java contains class libraries

9 7no!n as Java APIs $Application Programming Interfaces


10/29

8asics of a #3pical Java "nvironment

• Java programs normall3 undergo five phases

9 "dit

• Programmer !rites program $and stores program on dis/

9 0ompile

• 0ompiler creates bytecodes from program

9 %oad

• 0lass loader stores b3tecodes in memor3

9 =erif3

• =erifier ensures b3tecodes do not violate securit3re>uirements

9 "?ecute

• Interpreter translates b3tecodes into machine language


11/29

Typical Java environment.

Primar3

1emor3

.

.

.

.

.

.

2is/

2is/

2is/

"ditor

0ompiler

0lass %oader

Program is created in an editorand stored on dis/ in a file ending!ith .java.

0ompiler creates b3tecodes andstores them on dis/ in a file ending!ith .class.

0lass loader reads .class files containing b3tecodesfrom dis/ and puts thoseb3tecodes in memor3.

Phase :

Phase )

Phase *

Primar3

1emor3

.

.

.

.

.

.

83tecode =erifier 83tecode verifier confirms thatall b3tecodes are valid and donot violate Java@s securit3restrictions.

Phase

Primar3

1emor3

.

.

.

.

.

.

Interpreter Interpreter reads b3tecodesand translates them into alanguage that the computercan understand, possibl3storing data values as theprogram e?ecutes.

Phase B


12/29

Java

In discussing java it is important to distinguish bet!een

:. #he Java Programming %anguage

). #he Java =irtual 1achine

*. #he Java Platform


13/29

Java

:. #he Java Programming Language is the language in

!hich Java applications, applets , servlets andcomponents are !ritten. It is an object orientatedlanguage li/e 066.

). #he Java Virtual Machine, $or java interpreter is the

crucial piece of ever3 Java installation. Java applicationsare portable, but the3 are onl3 portable to platforms to!hich a java virtual machine $ or java interpreter hasbeen ported.

*. #he Java Platform . All programs !ritten in Java rel3 onthe set of predefined classes that comprise the javaplatform. #hese classes are organised into relatedgroups /no!n as packages. #he java platform definespac/ages for functionalit3 such as input(output,net!or/ing, graphics, user interface creation.


14/29

J=1

class my2ode 3

5

myCode.java

Compiled by Java

compiler

Application

runs

Application

runs

Interpreted

by JVM

Source

Code

1661166161661

myCode.class

Bytecode


15/29

J=1

• J=1 provides the run time environment for the b3tecode

$Java 4untime "nvironment J4"

9 e?ecutes the b3tecode and causes native machine

code instructions to e?ecute on the 0P& that the J=1

is on

each target platform needs an implementation of the

J=1


16/29

Java 0ompiler

class my2ode 3

5

myCode.java

Source

Code

Errors

2om"iler 7yte 2ode

8nter"reter for

2om"uter

(JVM)

8nter"reter for

2om"uter 7

(JVM)

8nter"reter for

2om"uter 2

(JVM)


17/29

Operation of the J4"$Java 4untime "nvironment

::::::

::::::::

myCode.java

Compile Class Loader

Bytecode verifier

Interpreter

::::::

::::::::

myCode.class

javac

RunTime

Hardare

%oad from

hard dis/,

net!or/ or

other source

Runtime

java


18/29

J4"

• At runtime the java b3tecode that ma/es up a java soft!are program

are

9 %oaded, chec/ed and run in an interpreter

9 In the case of applets 3ou can do!nload the b3tecode and the3 are then

interpreted b3 the J=1 built into the bro!ser.

• 83tecode verifier chec/s

9 Attributes correctl3 t3ped

9 8od3 of the methods chec/

9 #3pe chec/ing 9 4eferences to other t3pes chec/ed


19/29

Java Applications vs Java Applets• #here are t!o categories of Java Programs

9 A Java Application 9

• #hese are stand alone programs in the traditional sense

• 4un independentl3

• 4un under the java interpreter

9 Java applets

• #hese are programs designed to run from bro!sers such asCetscape or Sun@s 5otJava.

• #he3 don@t run independentl3

• Programs that can be included in !eb documents.


20/29

First Java Program $Application

• A class definition is the basic bloc/ of a Java program

• "ach program must have a main method to tell it!here to start e?ecuting

// First Program HelloWorld

public class HelloWorld {

public static void main(String args [!{

System.out.println("Hello #orld...$!%&

&


21/29

Cotes

• // First Program HelloWorld

• 0omments begin !ith ((

• 0an also use 0 st3le comments• /* First Program HelloWorld */


22/29

Cotes )

• public class HelloWorld

• This begins a class deinition or class

HelloWorld

• These classes are !no"n as Programmerdeined classes or #ser deined classes

• The public and class terms are java

!ey"ords "hich are al"ays lo"ercase• HelloWorld is the class identiier "hich

al"ays start "ith an uppercase letter


23/29

Cotes *

• Dhen 3ou save 3our class definition in a

file the filename must be the same as the

class identifier !ith a .java e?tension

• So the 5elloDorld class !ould be stored

in a 5elloDorld.java file


24/29

Cotes

• public static void main$%tring args &'(

• Java applications automatically begin e)ecuting atmain

• Parentheses $( ater main indicate a program piece

called a method "hich deine some operationalcomponent o the class.

• oid indicates that the method "ill perorm a tas!"ithout returning any inormation "hen it completes

• %tring args &' are used as input arguments to themethod. +n this case "e don,t use input but javare-uires it any"ay


25/29

Cotes B

• %ystem.out.println$Hello "orld...(0• %ystem.out is called the standard output object• This "ill display a line o te)t in the command

"indo"

• +n Java 1 any source and destination or +/2 isconsidered a stream o bytes or characters.• To perorm output "e insert bytes or characters

into a stream. To perorm input "e e)tract bytes orcharacters rom a stream.

• java.lang.%ystem class contains three predeinedstreams• %ystem.out• %ystem.err or errors• %ystem.in


26/29

A First Java Program

• #his is a Java application not a Java applet 9

indicated b3 presence of main

• Source code e?ists in a file !ith same name asthe class and an e?tension of .java. So for the

previous e?ample it is 5elloDorld.java

• Java is case sensitive $li/e 0.


27/29

&sing the J27

• 0reate source files for

each class in 3our

program• #he name of source file

should be the same as

the name of class

pu!lic class myCode "

#

#

#

#

$

myCode.java

Source File


28/29

0ompiling 3our source code

• 0ompile each class source

file into b3tecode $class files

• #o compile a java source file

javac m30ode.java

• #his creates a classfile called

m30ode.class

%&&%%&%&&%%%&%&%&%%

#

#

#

#

myCode.class

Class File


29/29

#o run 3our program

• #o start 3our program running 3ou run the

b3tecode of the program control class

• #he program control class has the main method

• #o run b3tecode 9 pass it to the J=1 java classFileCame

e.g. java m3Prog

note no .class included

03 Java - LN01startingpoint

Documents

Transcript of 03 Java - LN01startingpoint