Inheritance

Inheritance types, the super keyword, method overriding, and access modifiers in inheritance.

Definition

Inheritance allows a class (subclass) to acquire the properties and methods of another class (superclass). It promotes code reuse and establishes an “is-a” relationship.

class Subclass extends Superclass {
    // additional fields and methods
}

Types of Inheritance

• Single — One subclass extends one superclass.
• Multilevel — A subclass extends another subclass (chain).
• Hierarchical — Multiple subclasses extend the same superclass.

Java does not support multiple inheritance of classes. Use interfaces instead.

The super Keyword

• super.method() — Calls the superclass version of an overridden method.
• super(args) — Calls the superclass constructor from a subclass constructor.

Method Overriding

A subclass provides its own implementation of a method already defined in the superclass. The method signature must match exactly.

Access Modifiers in Inheritance

• public and protected members are inherited.
• private members are not directly accessible in subclasses.
• Default (package-private) members are inherited only within the same package.

Example

// InheritanceDemo.java
// Demonstrates inheritance and method overriding in Java.

// Superclass
class Animal {
	// Method in superclass
	void eat() {
		System.out.println("Animal eats");
	}
}

// Subclass extends superclass
class Dog extends Animal {
	// Overriding method
	void eat() {
		System.out.println("Dog eats bones");
	}
}

public class InheritanceDemo {
	public static void main(String[] args) {
		// Create Dog object and call eat()
		Dog d = new Dog();
		d.eat();
	}
}

Full source: examples/09-inheritance/InheritanceDemo.java