Static Variable vs Instance Variable

Let us understand the differences between static and instance variable.

Java language uses variables in different scopes: static scope, local scope, block scope. Java has different ways of storing data either as primitive data types or as Objects. Class specifies type of a object. Static variable is defined generically for the entire class and not for a specific object. Hence Static variables belong to a class and hence has the same value for all objects of the class. Instance (object) variables belong to a specific object.

Static variable	Instance variable
A static variable is a property of a class.	An instance variable is a property of an instance.
A static variable is created only once when the classloader loads the class.	An instance variable is created everytime an instance is created.
A static variable is used when you want to store a value that represents all the instances like count, sum, average etc.	An instance variable is used to store a value that represents property of single instance.

Declaring an static variable

static int countOfOrders;

Declaring an instance variable

String OrderId;

Let us consider the following example:

public class Order{
	//static variable
	static int countOfOrders;
	//instance variable
	String orderId;


	public static void main(String args[]){
		Order orderInst = new Order();
		//Assigning to static variable
		Order.countOfOrders = 10;
		//Assigning to instance variable
		orderInst.orderId="Ord1_11Nov2017_3578923";
		String name="Jan";//simple local variable. it is not instance and not static.
	}
}

Assigning to static variable

Order.countOfOrders = 10;
orderInst.countOfOrders= 11;

Both the above assignments work. However, Using the class name is the preferred approach.

Assigning to instance variable

orderInst.orderId="Ord1_11Nov2017_3578923";

Static Variable vs Instance Variable

Static Variable vs Instance Variable

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