Instance Variable in Java with Example

In this tutorial, I will be sharing what are instance variables in java, example of an instance variable, properties of instance variables in java, and default values for instance variables. Let's dive deep into the topic.

Read Also: Types of Variables in Java

What are Instance Variables in Java?

Instance variables are defined inside a class but outside any method declaration. These variables are defined without the static keyword and are only initialized when the class is instantiated i.e. object of that class is created. These variables belong to each unique object and have scope only within that object i.e not shared among instances.

'Property', 'Instance variable', 'Field', or 'Attribute' are the terms having the same meaning.

Example of Instance Variable in Java

The following code defines instance variables for the empName, empId for employee objects.

public class Employee {
    
    // Instance variable empName with public access modifier
    public String empName;
    // Instance variable empId with private access modifier
    private int empId;

}

Each instance of the Employee class can have its own unique values for those two fields.

Rules Associated With Instance Variable in Java

Instance variable can use any access modifiers (private, public, protected, or default).

Instance variable can be marked final

Instance variable can be marked transient

Instance variable cannot be marked static otherwise it will become a class variable.

Instance variable cannot be marked abstract

Instance variable cannot be marked synchronized

Instance variable cannot be marked strictfp

Instance variable cannot be marked native

Note: Any variable which is marked as static is called Class Variable because it has scope within the class.

Important Points About Instance Variable in Java

Instance variables belong to each unique object of the class.

Instance variables are created only when a new object is created using a 'new' keyword in Java.

Instance variables associated with an object are destroyed once the object is destroyed.

Instance variables will have a default value if not initialized.

Default Value of Instance Variable in Java

default values of instance variable in java

Java Program for Instance Variable

class InstanceExample
{
    /* Below variable is Instance variable as it 
    is inside the class and outside the method
    declaration. It is not using STATIC 
    keyword and using default access modifier*/
    // Declaring Instance Variable
    int instanceVariable;
    
    //Constructor for InstanceExample Class
    InstanceExample(int num)
    {
        this.instanceVariable = num;
    }
    
    //Method to display Instance Variable
    void printInstanceVariable()
    {
        System.out.println("Value of Instance Variable is "+instanceVariable);
    }
    
}

public class JavaHungry
{
    public static void main(String args[])
    {
        //Creating object of InstanceExample Class
        InstanceExample ob1 = new InstanceExample(5);
        InstanceExample ob2 = new InstanceExample(10);

        //Calling printInstanceVariable() for each object
        ob1.printInstanceVariable();
        ob2.printInstanceVariable();
    }
}

Output:
Value of Instance Variable is 5
Value of Instance Variable is 10

That's all for today. Please mention in comments in case you have any questions regarding the instance variable in java with example.

Reference:
Java Docs

Java Hungry