Inheritance in Java

Expert View

According to my experience, inheritance is not just a concept — it's the blueprint of design thinking in Object-Oriented Programming. Think of building a modern manufacturing system: you don’t rebuild every vehicle from scratch — you start with a Vehicle base class and then specialize into Car, Bus, or Truck. This principle of specialization and generalization forms the foundation of scalable software and real-world factories alike.

Inheritance drives reusability, consistency, and runtime polymorphism — the three pillars of robust design. My advice to every student: *Experiment, visualize, and build mini hierarchies in Java.* Watch how a simple class structure can model complex manufacturing lines at NBKRIST’s Innovation Labs we have in our college. 🚀

1. Introduction

Inheritance allows a new class to derive properties and behavior from an existing class. It’s like how every new vehicle model inherits standard safety and design features from its parent blueprint in an automotive factory.

class Vehicle { void start() { System.out.println("NBKRIST Vehicle starting..."); } } class Car extends Vehicle { void drive() { System.out.println("Car driving smoothly..."); } } public class Main { public static void main(String[] args) { Car c = new Car(); c.start(); c.drive(); } }

Output:
NBKRIST Vehicle starting...
Car driving smoothly...

2. Process of Inheritance

In Java, inheritance is implemented using the extends keyword. The subclass (child) inherits accessible members from the superclass (parent), forming a “is-a” relationship.

class Vehicle { int wheels = 4; } class Bus extends Vehicle { void showInfo() { System.out.println("NBKRIST Bus with " + wheels + " wheels."); } } public class FactoryDemo { public static void main(String[] args) { Bus b = new Bus(); b.showInfo(); } }

Output:
NBKRIST Bus with 4 wheels.

3. Types of Inheritance

• Single:👉 A subclass inherits properties and behaviors from a single parent class. Car extends Vehicle.

• Multilevel:👉 A class is derived from another derived class, forming a multi-layered chain. ElectricCar extends Car extends Vehicle.

• Hierarchical:👉 Multiple subclasses inherit from the same parent class, sharing its common features. Bus, Car, and Truck all extend Vehicle.

• Multiple:A class implements multiple interfaces to inherit behavior from multiple sources. Achieved through Interfaces in Java. class SmartCar implements GPS, Engine

4. Universal Superclass – Object Class

Every class in Java implicitly inherits from the Object class — much like every machine in a factory follows universal operational protocols. This class provides methods such as equals(), toString(), and hashCode().

class Vehicle { String model; Vehicle(String model) { this.model = model; } public String toString() { return "NBKRIST Vehicle Model: " + model; } } public class ObjectDemo { public static void main(String[] args) { Vehicle v = new Vehicle("Bus-XL"); System.out.println(v); } }

Output:
NBKRIST Vehicle Model: Bus-XL

5. Multilevel Inheritance

Multilevel inheritance represents a layered evolution — for instance, a Bus inherits from Vehicle, and a LuxuryBus inherits from Bus.

class Vehicle { void start(){ System.out.println("NBKRIST Vehicle starting..."); } } class Bus extends Vehicle { void move(){ System.out.println("Bus moving..."); } } class LuxuryBus extends Bus { void airCondition(){ System.out.println("AC running..."); } } public class MultiLevelDemo { public static void main(String[] args) { LuxuryBus lb = new LuxuryBus(); lb.start(); lb.move(); lb.airCondition(); } }

Output:
NBKRIST Vehicle starting...
Bus moving...
AC running...

6. Application of Keyword super

The super keyword lets a subclass access its superclass members — ideal for refining inherited behavior or invoking the parent constructor.

class Vehicle { Vehicle() { System.out.println("NBKRIST Vehicle created"); } void start() { System.out.println("Vehicle starting..."); } } class Car extends Vehicle { Car() { super(); System.out.println("Car ready for test drive!"); } void start() { super.start(); System.out.println("Car engine started successfully!"); } } public class SuperDemo { public static void main(String[] args) { new Car().start(); } }

Output:
NBKRIST Vehicle created
Car ready for test drive!
Vehicle starting...
Car engine started successfully!

7. Constructor Method and Inheritance

Constructors are not inherited but invoked in a sequence from parent to child using super(). This ensures proper initialization from general (Vehicle) to specific (Car).

class Vehicle { Vehicle() { System.out.println("NBKRIST Vehicle built"); } } class Car extends Vehicle { Car() { System.out.println("Car assembled"); } } class SportsCar extends Car { SportsCar() { System.out.println("SportsCar tuned for performance"); } } public class ConstructorChain { public static void main(String[] args) { new SportsCar(); } }

Output:
NBKRIST Vehicle built
Car assembled
SportsCar tuned for performance