Inheritance in Java

Introduction to Inheritance in Java

Inheritance in Java is one of the most powerful features of object-oriented programming. It allows a class to inherit fields and methods from another class, enabling code reuse, reducing redundancy, and establishing relationships between classes in a hierarchical structure.

What is Inheritance?

In Java, inheritance enables a class (known as a subclass or derived class) to acquire properties and behaviors from another class (known as a superclass or base class). The subclass can also override inherited methods to provide its own specific behavior.

Syntax of Inheritance

Inheritance is implemented using the extends keyword.

class Parent {
    void show() {
        System.out.println("Parent method");
    }
}

class Child extends Parent {
    void display() {
        System.out.println("Child method");
    }
}

    

Types of Inheritance in Java

Java supports the following types of inheritance:

• Single Inheritance
• Multilevel Inheritance
• Hierarchical Inheritance
• Multiple Inheritance (via Interfaces)

Single Inheritance

In single inheritance, a subclass inherits from one superclass. It is the most basic form of inheritance.

class Animal {
    void eat() {
        System.out.println("This animal eats food.");
    }
}

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

    

Multilevel Inheritance

In multilevel inheritance, a class inherits from a class which itself inherits from another class. This forms a chain of inheritance.

class Animal {
    void eat() {
        System.out.println("Animal eats.");
    }
}

class Mammal extends Animal {
    void walk() {
        System.out.println("Mammal walks.");
    }
}

class Human extends Mammal {
    void speak() {
        System.out.println("Human speaks.");
    }
}

    

Hierarchical Inheritance

In hierarchical inheritance, multiple subclasses inherit from a single superclass.

class Animal {
    void breathe() {
        System.out.println("Animals breathe.");
    }
}

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

class Cat extends Animal {
    void meow() {
        System.out.println("Cat meows.");
    }
}

    

Multiple Inheritance using Interfaces

Java does not support multiple inheritance with classes to avoid the "Diamond Problem". However, it can be achieved using interfaces.

interface Flyable {
    void fly();
}

interface Swimmable {
    void swim();
}

class Duck implements Flyable, Swimmable {
    public void fly() {
        System.out.println("Duck flies.");
    }

    public void swim() {
        System.out.println("Duck swims.");
    }
}

    

The super Keyword

The super keyword is used to call parent class methods, constructors, or access parent class fields when they are hidden by child class members.

class Parent {
    void display() {
        System.out.println("Parent class");
    }
}

class Child extends Parent {
    void display() {
        super.display();
        System.out.println("Child class");
    }
}

    

Advantages of Inheritance

• Promotes code reusability
• Reduces redundancy
• Supports method overriding for polymorphic behavior
• Helps in creating a logical class hierarchy

Conclusion

Inheritance in Java is essential for designing robust and scalable applications. By understanding different types of inheritance—single, multilevel, hierarchical, and multiple via interfaces—you can write cleaner, more organized, and reusable code. Mastery of inheritance will allow you to build better object-oriented designs and manage complexity more efficiently.