static Keyword in Java

• You can apply static keyword to variables, methods, nested classes, nested interfaces and blocks of code.
• It is not valid to define top-level classes, interfaces, and enum as static.
• Static members belong to a class and not to instances.

Static Variable in Java

• It is also known as a class variable.
• Static variables belong to a class and you can access even if no instance of a class is created.
• Static variables are shared by all the instances of the class. If any object makes a change to a static variable then all other objects see that change.
• You can access static variable without creating an object of a class.
• It can be used to count the number of instances of a class.
• A static variable is created when the class is loaded into memory.

Syntax of creating static variable-

access-modifier static data-type variable;

Example

static int counter;

Syntax of accessing static variable-

class-name.staticVariable;
or
object.staticVariable;

Example of static variable

public class StaticExample
{
	static int counter;
	public StaticExample()
	{
		counter++;
	}
	public static void main(String args[])
	{
		System.out.println("No of objects = "+StaticExample.counter);
		StaticExample se = new StaticExample();
		System.out.println("No of objects = "+se.counter);
		StaticExample se2 = new StaticExample();
		se2.counter=5;
		System.out.println("No of objects = "+se.counter);
	}
}

Output

No of objects = 0
No of objects = 1
No of objects = 5

Static Method in Java

• Like a static variable, a static method belongs to a class and not to a specific instance of the class.
• Static methods are defined to access and manipulate static members of a class.
• Similar to static variables, you can access static methods using the class name and object.
• It cannot access nonstatic or instance members of the class.
• Static methods are allowed to access only static members of the class.

Syntax

access-modifier static return-type methodName(parameters)
{
	//code to be written inside method
}

Example of static method

class Mathematics
{
	public static int add(int n1, int n2)
	{
		return n1 + n2;
	}
	public static int sub(int n1, int n2)
	{
		return n1 - n2;
	}
	public static void main(String args[])
	{
		System.out.println("Sum of 10 and 12 is "+Mathematics.add(10,12));
		System.out.println("Subtraction of 10 and 12 is "+Mathematics.sub(10,12));
	}
}

Output

Sum of 10 and 12 is 22
Subtraction of 10 and 12 is -2

Static Block

• A block of code enclose in braces and prefixed by static keyword is called static initializer block.
• You cannot initialize static variables in the constructor of a class, by the help of static initializer block you can initialize static variables.
• A class can have more than one static initializer blocks. And they are executed in the order of their appearance.

Syntax

static{
	//code to initialize static variables
}

Example of static initializer block

public class Bonus
{
	private static int reward;
	static{
		reward = 10;
	}
	public static void main(String args[])
	{
		System.out.println("Reward Point = "+Bonus.reward);
	}
}

Output

Reward Point = 10

Difference between static method and instance method