Basic Concept of Java Pargramming

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Java

Background of this Blog

A.     Distinguish between valid & invalid identifiers?

B.      List of eight primitives types?

C.      Defines literal values for numeric and textual types?

D.     Define the terms variables and reference variable?

Identifiers

“An identifier is a name given to a variable class or method.”

Identifiers have the following characteristics:

Can start with a Unicode letter, underscore (_), or dollar sign ($)

Are case-sensitive and have no maximum length.

Example of valid identifiers:-

ü  identifier

ü  username

ü  user_name

ü  _sys_var1

ü  $chnage

Java programming language supports two basic data types:-

1.      Primitive types

2.   Class types

“Primitive data types are simple values, not objects.”

Ø  The java programing language defines eight primitive data types, which can considered in four categories:

Logical - Boolean

Textual - char

Integral - byte, short, int and long

Floating - double and float

“Class types are used for more complex types, including all the types that you declare yourself.”

ü They are used to create objects.

Ways of declare variables, Declarations, & Assignments.

Public class Assign

{

Public static void main(String[]args)

{

//declare and assign values to int

Integer variables int x=6, y=1000;

//declare and assign floating value

Float z=3.414f;

//declare and assign value to Boolean

Boolean truth=true;

//declare and assign value to char variable

Char c=’A’;

}

}

Ø  In java programming, beyond primitive types all other types are reference types.

Ø  A reference variable contains a handle to an object.

Example:

Public class MyDate

{

Private int day=9;

Private int month=11;

Private int year=1991;

Public MyDate(int day, int month, int year)

{…………..}

Public String tostring()

{…………}

}

Public class TestMyDate

{

Public static void main(String[]args)

{

MyDate today=new MyDate(9,11,1991);        // create object of MyDate Class

}

}

Ø  Variable “today” is a reference variable holding one object of “MyDate” class