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Class Inheritance >
Siva Nookala - 14 Mar 2016
As discussed in Java Class Inheritance Java supports inheritance to provide a hierarchy for class definition and hence avoiding duplicate code and increasing maintainability. There is no limit on the levels of hierarchy. We could have class D extend from class C, which in turn extends from class B, which in turn extends from class A. e.g., MountainBike extends from Bike, Bike extends from RegisteredVehicle, RegisteredVehicle extends from Vehicle.

The following program shows how we could implement multi-level inheritance.
Vehicles Hierarchy
class TestVehiclesHierarchy
    public static void main(String arg[])
        MountainBike mb = new MountainBike();
        mb.numberOfWheels = 2;
        mb.registrationNumber = "APXX WWW";
        mb.hasHelmet = true;
        mb.maxElevation = 3000.0;
        System.out.print("Mountain Bike with registration Number " + mb.registrationNumber);
        System.out.println(" is supported till the elevation of " + mb.maxElevation + " feet.");    

class Vehicle
    int numberOfWheels;

class RegisteredVehicle extends Vehicle
    String registrationNumber;

class Bike extends RegisteredVehicle // LINE A
    boolean hasHelmet;

class MountainBike extends Bike
    double maxElevation;

class Car extends RegisteredVehicle
    boolean hasAC;

class Cycle extends Vehicle
    boolean hasBackSeat;

Mountain Bike with registration Number APXX WWW is supported till the elevation of 3000.0 feet.


This program shows how to implement multi level inheritance. Initially Vehicle class is defined. RegisteredVehicle extends from Vehicle, Bike extends from RegisteredVehicle and MountainBike extends from Bike. So a MountainBike is a Bike, which in turn is a RegisteredVehicle, which in turn is a Vehicle. We also defined Car which extends from RegisteredVehicle and Cycle which extends from Vehicle.

  • Add double maxSpeed to Vehicle and see if we can initialize and print in the main method.
  • Change LINE A from class Bike extends RegisteredVehicle to class Bike extends RegisteredVehicle, Cycle and see what compilation error you get.
The class hierarchy in the above program when shown in a diagram will look like. Vehicles-multi-level-hierarchy
Please note that multi-level inheritance is different from multiple inheritance. Multiple inheritance which means inheriting from two classes is not supported in the Java. Although C++ supports multiple inheritance, it is intentionally not supported in java, since it adds lots of complexity.

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