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Inheritance & Method Overriding in Java

intermediate· OOP · Inheritance

Problem

Method overriding lets a subclass provide its own implementation of a method already defined in its parent class.

Create a base Animal class and a Dog subclass that overrides its behavior.

Java Program

Java

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

class Dog extends Animal {
    @Override
    void sound() {
        // Overrides Animal's version with Dog-specific behavior
        System.out.println("The dog barks");
    }
}

public class InheritanceDemo {
    public static void main(String[] args) {
        // Declared as Animal, but the actual object is a Dog
        Animal a = new Dog();
        // Java resolves sound() using the object's real (runtime) type
        a.sound();
    }
}

▶ Run Code

Output

The dog barks

Core Logic

This is runtime polymorphism in action — a subclass overrides a parent method, and Java picks the subclass's version even when the reference is typed as the parent.

How It Works

1class Dog extends Animal makes Dog a subclass that inherits everything Animal defines.
2@Override void sound() replaces the inherited method with Dog-specific behavior; the annotation lets the compiler catch signature mismatches.
3Animal a = new Dog(); declares the variable as type Animal, but the object it points to is actually a Dog.
4When a.sound() is called, Java resolves the method using the object's actual runtime type, not the variable's declared type.

Even though a is declared Animal, calling a.sound() prints "The dog barks", not a generic Animal message.

💡

Key Point: This is dynamic method dispatch — the JVM decides which overridden method to run based on the object's real class, at runtime.

Key Concepts

extends@Overrideruntime polymorphism

Interview Questions

What rules must an overriding method follow?

The same name and parameter list, a return type that is the same or a subtype, and access that is no more restrictive than the parent's. @Override makes the compiler check all of this.

How do you call the parent's version of an overridden method?

Use super.methodName(...). A common pattern is to extend the parent's behaviour rather than replace it completely.

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Learn the Concept

📘 Method Overriding 📘 Overloading vs Overriding 📘 Polymorphism

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