Question

Explain an Is-a relationship between classes in Java

Answer 1

Is-a relationship between classes:

Inheritance is Java can be done by implementing either Class Inheritance or Interface Inheritance. The notion of Is-a of classes is based on the Inheritance in Java. In Java, we can implement Is-a relationship between classes using the extends keyword or implements keyword in a class declaration.

It signifies that a child class will inherit all attributes and methods of the parent class, and this relationship is unidirectional in nature, for example, A car is a vehicle. But the reverse is not true, ie All vehicles are not a car.

Example:

package transport;

//Declare a parent class Vehicle
class Vehicle{    
    private double price; 
    public void setPrice(double  price) {
        this.price= price;
    }
    public double getPrice() {
        return price;
    }
}

//Car has Is-a relationship with Vehicle
//Car inherits price from parent class Vehicle

Class Car extends Vehicle{
   private String colour;
   public void setColour(String colour) {
        this.colour= colour;
    }
   public void getColour() {
        return colour;
    }
}