Basic Computationc( Variables and Expressions )

~VARIABLES~


*Variables is a storage location to hold a temporary values.
*It used to store data such as number and letters.
*They are implemented as memory locations.
*The data stored by a variable is called its value.
*The value is stored in the memory location.
*Its value can be changed.
*All variables must be declared before they can be used.


#The type of variable:

#SIMPLE OF DECLARATION VARIABLE JAVA PROGRAM

~CONSTANTS~

*Similar to variables but once initialized, their contents may 

NOT be changed.

*Declared with the reserved word final

*Syntax:

   final datatype CONSTANTNAME = value

*Example:

   final double CENTIMETERS_PER_INCH =2.54;

 final int NO_OF_STUDENTS = 20;

 final char BLANK = ' ';

   final double PAY_RATE =15.75;

~DATA TYPE~

*A data type specifies a set of values and their operations.

*Has two main kinds of data:1)class type  2)primitive types.

*A class type is used for a class of objects and has both data and methods.

="Java is fun" is a value of class type String

*A primitive type is used for simple,nondecomposable value such as an 

individual number or individual character.

=int, double, and char are primitive types.

# PRIMITIVE TYPES

example for primitive type

*Four type for integers,namely, byte, short, int, long.The only 

differences among the various integer types are the range of integers they

 represent and the amount of computer memory they used.

*A number having a fraction part such as the number 9.99, 3.14159,

-5.67 and 5.0 is called a floating point number.Java have two data 

types for floating point numbers,float and double.

*Char is used for single characters such as letters, digits, or punctuation.

*Boolean has two values, true and false.

EXAMPLE

~JAVA IDENTIFIER~

*An identifier is a name such as the name of a variable.

*Identifiers may contain only

     =Letters

     =Digit (0 through 9)

     =The underscore character ( _ )

     =And the dollar sign symbol ( $ ) which has a special meaning

*The first character cannot be a digit.

*Identifiers may not contain any spaces, dots (.),asterisks (*), or other

 characters.

*Since Java is case sensitive,stuff ,Stuff  and STUFF are

different identifiers.

#LEGAL AND ILLEGAL VARIABLE NAMES

#Assignment Statements

*An assignment statement is used to assign a value to a variable

       answer = 42;

*The "equal sign" is called the assignment operator.

*We say, "The variable named answer is assigned a value of 42," or

 more simply,"answer is assigned 42."