Java – Variables and Data Types

In this, java variables and data types tutorial, we learn how to declare a variable in java and what is data types in java. Let’s start with an example to declare variable and data type.

Example: Addition of two numbers.

class VarDemo	//creating a class
	public static void main(string arg[])	//define main method 
		//declare variables
		int a,b,c;

In the above example you need to look at the first line in main() method that is int a,b,c;

  • int – This is called a data type.
  • a,b,c – These are known as variables.

Now, let’s learn about variable and data type.

What is a Variable?

The benefit of variables is to store values than further, we can refer multiple times anywhere in the program, whenever required.

  • The variable is a memory location.
  • It can store values like numbers and text.
  • The value of a variable can be changed during programming.
  • All variables must be declared before use.
  • The variables always assigned values with the equal(=) sign.

Naming Rules for Variable

  • Name of a variable can be a combination of letters, numbers and underscore.
  • The first character of a variable name should not be a number, it must start with a character or underscore.
  • A variable name can have both uppercase and lowercase or a combination of both cases.
  • Variable name should not be a reserved keyword (predefined word in Java, like void and break).
  • Name of the variable should be meaningful.

Data Types in Java.

Whenever we declare a variable, we must specify the data type of that variable in Java. So, the question is what is a data type, type of data to be store in a variable is known as the data type. We must specify that the variable will store number, text or boolean values as a data type. In Java, there are two types of the data type.

  • Primitive Data Type
  • Abstract Data Type (Non-Primitive)

Primitive Data Type

There is a total of eight primitive data types in Java.

Data TypeSize in BytesDescription and Range
boolean1Store true or false
byte1Whole Numbers between -128 to 127
short2Whole Numbers between -32,768 to 32,767
int4Whole Numbers between -2,147,483,648 to 2,147,483,647
long8Whole numbers between -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float4Fractional numbers, store upto 7 decimanl digit
double8Fractional numbers, store upto 15 decimal digit
char2Single characters

Abstract Data Type (Non-Primitive)

Abstract data types are based on primitive data types.
String, Array, classes.

Example: Example of data type and variables.

class Example {
	public static void main(String arg[]) {
		boolean a=true;
		byte b=10;
		short c=25000;
		int d=50000;
		long e=100000L;	//long value should end with L.
		float f=1.44f;	//float value should end with f.
		double g=45000.55d;	//double value shold end with d;
		char h='A';	//store only single character, should be in sigle inverted comma.
		String name="Coder Mantra";	//Store text value, should be in double inverted comma.