Java Tutorial 9 – Variables

A variable can be thought of as a container which holds value for you during the life of your program.Every variable is assigned a data type which designates the type and quantity of a value it can hold.

The different Data Type are —

Integer data types

byte (1 byte)

short (2 bytes)

int (4 bytes)

long (8 bytes)

java-varaibles

Floating Data type

float (4 bytes)

double (8 bytes)

Textual Data Type

char (2 bytes)

Logical

boolean (1 byte) (true/false)

Points to Remember:

  • All numeric data types are signed(+/-).
  • The size of data types remain the same on all platforms (standardized)
  • char data type in Java is 2 bytes because it uses UNICODE character set. By virtue of it, Java supports internationalization. UNICODE is a character set which covers all known scripts and language in the world
To use a variable in your program you need to perform 2 steps
  1. Variable Declaration
  2. Variable Initialization

1) Variable Declaration

To declare a variable , you must specify the data type & give the variable a unique name.

Vriable-Type-Name-Declaration

Examples of other Valid Declarations are

int a,b,c;

float pi;

double d;

char a;

2) Variable Initialization:

To initialize a variable you must assign it a valid value.

java-variable-initialization

Example of other Valid Initializations are

pi =3.14f;

do =20.22d;

a=’v’;

You can combine variable declaration and initialization.

java-variable-initialization-declaration-combined

Example :

int a=2,b=4,c=6;

float pi=3.14f;

double do=20.22d;

char a=’v’;

Variable Type Conversion & Type Casting

A variable of one type can receive the value of another type.Here there are 2 cases -

case 1) Variable of smaller capacity is be assigned to another variable of bigger capacity.

java-type-conversion

This process is Automatic, and non-explicit is known as Conversion

case 2) Variable of larger capacity is be assigned to another variable of smaller capacity

java-type-cast-operator

In such cases you have to explicitly specify the type cast operator. This process is know as Type Casting.

In case, you do not specify a type cast operator, the compiler gives an error. Since this rule is enforced by the compiler , it makes the programmer aware that the conversion he is about to do may cause some loss in data and prevents accidental losses.

Assignement: To Understand Type Casting

Step 1) Copy the following code into an editor.

class Demo{
 public static void main(String args[]){
 byte x;
 int a=270;
 double b =128.128;
 System.out.println("int converted to byte");
 x=(byte) a;
 System.out.println("a and x "+ a +" "+x);
 System.out.println("double converted to int");
 a=(int) b;
 System.out.println("b and a "+ b +" "+a);
 System.out.println("n double converted to byte");
 x= b;
 System.out.println("b and x "+b +" "+x);
 }
}

Step 2) Save, Compile & Run the code.

Step 2) Error =? Try to debug. Hint – Typecasting is missing for one operation.

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