What is a variable in Java?

It is defined as a container that can hold any type of data. As the name implies, we can alter the value stored in the variable.

Key Points:-

It is a name given to the location in the memory in which we store data.

Declaration of Variable:- To declare a variable first write datatype ( type of data i.e. int,
float, char, etc.) then space (“ ”), and then write the name of the variable (Identifier).
Syntax:

 datatype variable_name;

Example:

 int a;

Initialization of Variable: - To initialize a variable we have to assign a value to the variable.
Syntax:

variable_name = value;

Example:

var = 12;

Example of Declaration and Initialization of the variable at once:

int a=20;
String s="Hello";

Types of Variables

Variables are of three types: Instance, Local, Static
1. Instance Variable: - Variable declared within a class but outside of any methods.

Example:

package quipohouse;
public class InstanceVariable {
	int var = 10;    // Declaration and initialization of instance variable

	public static void main(String[] args) {
		InstanceVariable c = new InstanceVariable();
		System.out.println(c.var);
	}
}

Output:

2. Local Variable: -Variable declared inside any method or block. The scope of the local variable is inside that method or block.
Example:

package quipohouse;
public class LocalVariable {

	public static void main(String[] args) {
		int var2 = 12; // Declaration and initialization of Local Variable
		System.out.println(var2);
	}
}

Output:

3. Static Variable:

A variable marked with a static keyword is known as a static variable. e.g. - static int var;
The static variable is declared inside a class but outside any method.
The scope of the static variable is inside the class.
We can have only one copy of the static variable of any class, independent of the number of objects we create.
As a result, if we make any changes to a static variable in one object then it
will reflect back on another variable.
We can directly access static variables by using the class name.
We can also access static variables without using the class name within a class inside the static block. In this scenario compiler automatically append the class name before it.

Example:

package quipohouse;
public class StaticVariable {
	static int var; // Declaration of static variable

	public static void main(String[] args) {
		System.out.println(StaticVariable.var); // 20
		System.out.println(var); // 20
	}
}

Output:

0
0