OVER VIEW OF JAVA

UNIT – 1 CONTINUED …..: 

UNIT – 1 CONTINUED ….. OVERVIEW OF JAVA INTRODUCTION SIMPLE PROGRAM STRUCTURE JAVA TOKENS JAVA STATEMENTS JAVA VIRTUAL MACHINE SUMMARY

INTRODUCTION: 

INTRODUCTION WE CAN DEVELOP TWO TYPES OF JAVA PRGMS STAND ALONE APPLICATIONS WEB APPLETS STAND ALONE APPLICATION PRGMS WRITTEN FOR SPECIFIC TASK AND CARRY OUT IN STAND ALONE MACHINES. EXECUTING A STAND ALONE PRGM INVOLVE TWO STEPS 1.COMPILING SOURCE CODE INTO BYTECODE USING JAVAC COMPILER 2.EXECUTING BYTECODE PRG USING JAVA INTERPRETER.

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CONTINUED ….. WEB APPLETS 1.DEVELOPED FOR INTERNET APPLICATIONS 2.AN APPLET LOCATED ON DISTANT COMPUTER(SERVER) CAN BE DOWNLOAD THRU INTERNET AND EXECUTE ON LOCAL COMPUTER(CLIENT). 3.APPLET PROGRAMS CAN RUN ONLY IN BROWSER.

SIMPLE JAVA PROGRAM: 

SIMPLE JAVA PROGRAM class sample { public static void main (String args[]) { System.out.println (“Welcome to Java “); } }

DESCRIPTION: 

DESCRIPTION CLASS DECLARATION class sample 1.OBJECT ORIENTED CONSTRUCT 2.EVERY THING MUST PLACE INSIDE A CLASS. 3.CLASS IS A KEYWORD. 4.PRGM NAME AND CLASS MUST BE IN SAME NAME. OPENING BRACE EVERY CLASS DEFINITION IN JAVA BEGINS WITH “ { “ AND ENDS WITH “}”

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CONTINUED ….. MAIN LINE public static void main (String args[]) main :- STARTING POINT FOR INTERPRETER TO BEGIN THE EXECUTION public :- ITS AN ACCESS SPECIFIER THAT STATES MAIN METHOD IS UNPROTECTED. static : -DECLARES THIS METHOD AS ONE THAT BELONGS TO ENTIRE CLASS void :-MAIN METHOD DOES NOT RETURN ANY VALUE. String args[] :- CONTAINS AN ARRAY OF OBJECTS OF CLASS TYPE STRING.

CONTINUED …..: 

CONTINUED ….. OUT PUT LINE :- System.out.println ( “ “); 1.USED TO PRINT THE MESSAGE OR RESULT ON SCREEN 2.PRINTLN – APPENDS A NEWLINE CHARACTER. 3.EACH AND EVERY STATEMENT ENDS WITH SEMICOLON.

JAVA PROGRAM STRUCURE: 

JAVA PROGRAM STRUCURE DOCUMENTATION SECTION PACKAGE STATEMENT IMPORT STATEMENTS INTERFACE STATEMENTS CLASS DEFINITIONS MAIN METHOD CLASS { MAIN METHOD DEFINITION }

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CONTINUED ….. DOCUMENTATION SECTION ;- COMMNET LINES PACKAGE STATEMENT :- INFRMS COMPILER THAT CLASSES DEFINED HERE BELONG TO THIS PACKAGE. EG : package student ; IT IS OPTIONAL IMPORT STATEMENT :- SIMILAR TO # INCLUDE IN C INTERFACE STATEMENT :-INCLUDES GROUP OF METHOD DECLARATION AS LIKE CLASS CLASS DEFINITION :- CLASSES ARE USED TO MAP OBJECTS. MAIN METHOD CLASS :-CREATES OBJECT OF VARIOUS CLASSES AND COMMUNICATE BETWEEN THEM.