What is Is-A-Relationship in Java?

Last Updated : 01 Dec, 2021

A relationship in Java means different relations between two or more classes. For example, if a class Bulb inherits another class Device, then we can say that Bulb is having is-a relationship with Device, which implies Bulb is a device.

In Java, we have two types of relationship:

Is-A relationship: Whenever one class inherits another class, it is called an IS-A relationship.
Has-A relationship: Whenever an instance of one class is used in another class, it is called HAS-A relationship.

Is-A relationship

IS-A Relationship is wholly related to Inheritance. For example – a kiwi is a fruit; a bulb is a device.

IS-A relationship can simply be achieved by using extends Keyword.
IS-A relationship is additionally used for code reusability in Java and to avoid code redundancy.
IS-A relationship is unidirectional, which means we can say that a bulb is a device, but vice versa; a device is a bulb is not possible since all the devices are not bulbs.
IS-A relationship is tightly coupled, which means changing one entity will affect another entity.

Advantage of IS-A relationship

Code Reusability.
Reduce redundancy.

How to achieve IS-A relationship

IS-A relationship can simply be achieved by extending an interface or class by using extend keyword.

Let’s understand the IS-A relationship with the help of a flowchart –

In the above flowchart, the class Bulb extends class Device, which implies that Device is the parent class of Bulb, and Class Bulb is said to have an Is-A relationship. Therefore we can say Bulb Is-A device.

Implementation of IS-A relationship

1. Class Device has a field named as deviceName.

2. Class Bulb extends Device that means Bulb is a type of Device.

3. Since Device is the parent class which implies that class Device can store the reference of an instance of class Bulb.

Example: Here is the implementation of the same, which is as follows:

Java

// Java program to demonstrate the  
// working of the Is-A relationship 
  
import java.io.*; 
  
// parent class 
class Device { 
  
    private String deviceName; 
  
    public void setDeviceName(String deviceName) 
    { 
        this.deviceName = deviceName; 
    } 
  
    public String getDeviceName() 
    { 
        return this.deviceName + " is a Device"; 
    } 
} 
  
// child class 
class Bulb extends Device { 
    public static void main(String gg[]) 
    { 
        // parent class can store the reference 
        // of instance of child classes 
        Device device = new Bulb(); 
        
        // set the device name to bulb 
        System.out.println("Device name is Bulb"); 
        device.setDeviceName("Bulb"); 
        
        // print the device name 
        System.out.println(device.getDeviceName()); 
    } 
}

Output

Device name is Bulb
Bulb is a Device

In the above java program Bulb class inherits the Device class. Therefore, we can say that Bulb is having an IS-A relationship with the class Device. Hence Bulb is a Device.