Java Variables, Datatypes & Keywords

Before we write our first Java program, we shall first start with the definition ofVariables & Keywords and their uses.

What is a Variable?

  •  A variable is a container which has a size, and a datatype and it is used to hold primitive data or reference to objects. Each variable has a memory location to store its data or value.
  • The variables which holds primitive datatype values such as int, long, boolean, short etc.. are called asPrimitive variables. This variable stores the value in its memory location.
  • The variables which holds references to the objects is said to be Reference Variables. This variables doesn’t store the object itself in its memory location. It stores the address of the another memory location where the actual value is present.

How to declare and initialize a Variable?

datatype variablename = initialvalue; Examples:

int a =1;boolean b =true;

What is a Datatype?

A datatype is defined as the type of value a variable can hold in it. Primitive and Reference are the two datatypes present in java.

Primitive Datatypes:

Below are the eight primitive predefined datatypes used in java language named by a reserved keyword.

Datatype Size (in bits) Range
byte 8 -128 to 127
short 16 -32768 to 32767
int 32 -231 to 231-1
long 64 -263 to 263-1
float 32 1.40129846432481707e-45 to 3.40282346638528860e+38
double 64 4.94065645841246544e-324d to 1.79769313486231570e+308d
boolean 1 true or false
char 16 ‘\u0000′(0) to ‘\uffff’(65535)

Reference Datatypes:

These are the datatypes which can be referred to any object or in simple words it is the name of any class named other than the standard Java keywords.

What is a Keyword?

Keyword is a predefined words that are reserved by Java for its own use. Below are the list of keywords used in Java programming language.

abstract continue for new switch
assert default goto package synchronized
boolean do if private this
break double implements protected throw
byte else import public throws
case enum instanceof return transient
catch extends int short try
char final interface static void
class finally long strictfp volatile
const float native super while

Posted on July 1, 2014 in Java for Beginners

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