What is Inheritance?

Inheritance allows a class (called a subclass or child class) to inherit fields and methods from another class (called a superclass or parent class).

Java uses the extends keyword to define this relationship.

Benefits of Inheritance

• Code reuse: Common behavior resides in the parent.

• Hierarchy modeling: Naturally represent "is-a" relationships.

• Flexibility: Subclasses can override or extend behavior.

class Animal {
    void makeSound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Dog barks");
    }
}

Usage:

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();
        d.makeSound(); // Inherited
        d.bark();      // Own method
    }
}

The super Keyword

You can use super to:

• Call a superclass method.

• Call a superclass constructor (from a subclass constructor).

class Animal {
    Animal() {
        System.out.println("Animal constructor called");
    }
}

class Cat extends Animal {
    Cat() {
        super(); // Calls Animal constructor
        System.out.println("Cat constructor called");
    }
}

Rules of Inheritance in Java

• Java supports single inheritance only (one parent class per subclass).

• Constructors are not inherited, but can be called using super().

• Private members of the superclass are not accessible in the subclass directly.

Summary

• Inheritance models "is-a" relationships and enables code reuse.

• Use extends to create a subclass.

• Subclasses inherit accessible fields and methods from the parent class.

• Use super to reference the parent class.

Assignment: Lesson 4 – Inheritance

Objective:

Understand how to create subclasses, use extends, and invoke inherited methods.

Part 1: Conceptual Questions

Write short answers in a comment or text file:

1. What is the purpose of inheritance in OOP?

2. What does the extends keyword do?

3. Can a subclass inherit private fields from a superclass?

Part 2: Coding Task

Create a superclass called Vehicle with:

• Fields: brand (String)

• Method: drive() that prints brand + " is driving"

Create a subclass called Car that:

• Inherits from Vehicle

• Has its own method playMusic() that prints "Playing music"

In the main() method:

• Create a Car object

• Set the brand to "Tesla"

• Call both drive() and playMusic()

Github: https://github.com/tuanbeovnn/java-bootcamp/tree/java-bootcamp-oop-chapter4