What is a Variable?

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.

In this tutorial, you will learn-

Data types in java

The different Data Type are ---
Integer java data types
byte (1 byte)

short (2 bytes)

int (4 bytes)

long (8 bytes)

Java Variables and Data Types

Floating Data type

float (4 bytes)

double (8 bytes)

Textual Data Type

char (2 bytes)

Logical

boolean (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

Variable in program 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.
 

Java Variables and Data Types

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 Variables and Data Types

Example of other Valid Initializations are

pi =3.14f;

do =20.22d;

a=’v’;

You can combine variable declaration and initialization.
 

Java Variables and Data Types

Example :

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

float pi=3.14f;

double do=20.22d;

char a=’v’;

Java 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 Variables and Data Types

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 Variables and Data Types

In such cases you have to explicitly specify the type cast operator. This process is known 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.

Assignment: 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 3) Error =? Try to debug. Hint - Typecasting is missing for one operation.

 

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