Method Overriding

Reading Time: 9 Minutes Difficulty: Beginner

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Topic Summary

Method overriding happens when a child class provides its own specific version of a method that already exists in the parent class. The child says: "I know you (parent) have a speak() method, but I'm going to do it MY way." This is the heart of runtime polymorphism - Java decides which version to call based on the actual object type, not the variable type.

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What You'll Learn

• What method overriding is and why it's powerful
• The rules that a valid override must follow
• The @Override annotation and why you should use it
• What covariant return type means
• Which methods cannot be overridden

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Prerequisites

• Inheritance (Lesson 05)
• super Keyword (Lesson 06)

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Explanation

What Is Method Overriding?

When a child class defines a method with the exact same name, exact same parameters, and a compatible return type as a method in its parent class, it overrides that method.

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

class Dog extends Animal {
    @Override
    void speak() {  // OVERRIDES Animal's speak()
        System.out.println("Dog says: Woof!");
    }
}

class Cat extends Animal {
    @Override
    void speak() {  // OVERRIDES Animal's speak()
        System.out.println("Cat says: Meow!");
    }
}

When you call speak() on a Dog, Java runs Dog's version. When you call it on a Cat, Java runs Cat's version. The parent's generic version is replaced by the child's specific one.

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The Rules for Valid Overriding

For an override to be valid, ALL of these must be true:

Rule	Explanation
Same method name	Must be exactly the same name
Same parameter list	Same number, types, and order of parameters
Same or covariant return type	Same return type, OR a subtype (child type)
Same or less restrictive access	Can make it more public, never more private
Cannot throw broader exceptions	Can throw fewer/narrower checked exceptions

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The @Override Annotation

@Override is an annotation you place above an overriding method. It tells the Java compiler: "I intend to override a parent method here - please verify this is correct."

@Override
void speak() {
    System.out.println("Dog says: Woof!");
}

Why use it?

• If you accidentally misspell the method name or change parameters, the compiler throws an error
• Without it, Java would silently treat it as a new method, not an override!

class Dog extends Animal {
    // TYPO! This is NOT overriding - it's a new method called 'speek'
    void speek() {  // Without @Override, no error!
        System.out.println("Dog says: Woof!");
    }
}

Always use @Override - it's free protection.

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Runtime Polymorphism (Dynamic Method Dispatch)

This is where the magic happens. When you have a parent type reference pointing to a child object, Java decides which method to call at runtime (not compile time), based on the actual object:

Animal a = new Dog();  // Parent reference, Child object
a.speak();             // Which speak() is called? → Dog's! (decided at runtime)

This is called dynamic method dispatch. Java looks at the actual object type (Dog), not the reference type (Animal), to pick the method.

Animal[] animals = {
    new Dog(),
    new Cat(),
    new Animal()
};

for (Animal a : animals) {
    a.speak();  // Each calls its OWN version - resolved at runtime
}

Output:

Dog says: Woof!
Cat says: Meow!
Some animal makes a sound.

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Covariant Return Type

Since Java 5, an overriding method can return a subtype of the parent's return type. This is called covariant return type.

class Animal {
    Animal create() {
        return new Animal();
    }
}

class Dog extends Animal {
    @Override
    Dog create() {  // Returns Dog (subtype of Animal) - valid override!
        return new Dog();
    }
}

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Methods That CANNOT Be Overridden

Modifier	Reason Cannot Override
private	Not visible to child class at all
static	Belongs to the class, not objects; only hidden, not overridden
final	Explicitly marked "do not override"

class Parent {
    private void secret() { ... }       // can't override - child can't see it
    static void classMethod() { ... }   // can't override - only hide
    final void lockedMethod() { ... }   // can't override - compiler error
}

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Real-World Analogy

Think of a restaurant franchise.

The parent company (Animal) has a standard recipe for "Burger" that all restaurants should have. But each specific location (Dog, Cat) can override that standard recipe with their local specialty version. When a customer walks into a specific location and orders a "Burger," they get that location's version - not the generic headquarters version.

That's method overriding: the same "menu item" name, but each subclass serves its own version.

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Code Example

// Parent class
class Shape {
    String color;

    Shape(String color) {
        this.color = color;
    }

    // This will be overridden
    double area() {
        return 0.0;
    }

    void displayInfo() {
        System.out.println("Color: " + color + ", Area: " + area());
    }
}

// Circle overrides area()
class Circle extends Shape {
    double radius;

    Circle(String color, double radius) {
        super(color);
        this.radius = radius;
    }

    @Override
    double area() {
        return Math.PI * radius * radius;
    }
}

// Rectangle overrides area()
class Rectangle extends Shape {
    double width, height;

    Rectangle(String color, double width, double height) {
        super(color);
        this.width = width;
        this.height = height;
    }

    @Override
    double area() {
        return width * height;
    }
}

// Triangle overrides area()
class Triangle extends Shape {
    double base, height;

    Triangle(String color, double base, double height) {
        super(color);
        this.base = base;
        this.height = height;
    }

    @Override
    double area() {
        return 0.5 * base * height;
    }
}

public class Main {
    public static void main(String[] args) {
        // Parent references, child objects - runtime polymorphism!
        Shape[] shapes = {
            new Circle("Red", 5),
            new Rectangle("Blue", 4, 6),
            new Triangle("Green", 3, 8)
        };

        for (Shape s : shapes) {
            s.displayInfo();  // Each calls ITS OWN area() - resolved at runtime
        }
    }
}

Output

Color: Red, Area: 78.53981633974483
Color: Blue, Area: 24.0
Color: Green, Area: 12.0

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Common Mistakes

• Mistake: Not using @Override and accidentally creating a new method with a typo → Fix: Always add @Override - the compiler will catch naming mistakes.
• Mistake: Trying to override a private or final method → Fix: private methods are invisible to child classes; final methods are locked. Neither can be overridden.
• Mistake: Confusing overriding with overloading → Fix: Overriding = same method signature in child class. Overloading = same method name with different parameters in the SAME class.

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Best Practices

• Always use @Override when overriding - treat it as mandatory, not optional
• Call super.method() when you want to extend (not replace) the parent's behavior
• Don't override just to do nothing - if a method makes no sense in the child, reconsider the design
• Keep overriding methods focused - they should do what their name says

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Interview Questions

Q: What is method overriding in Java? A: Method overriding is when a child class provides its own implementation for a method that is already defined in its parent class. The overriding method must have the same name, same parameter list, and a compatible return type. It enables runtime polymorphism.

Q: What is dynamic method dispatch? A: Dynamic method dispatch (runtime polymorphism) is when Java determines which overridden method to call at runtime based on the actual object type, not the reference type. If Animal a = new Dog() and you call a.speak(), Java calls Dog's speak() because the actual object is a Dog.

Q: Can you override a static method in Java? A: No. Static methods belong to the class, not to objects. A child class can define a static method with the same name (called method hiding), but this is not true overriding - dynamic dispatch does not apply to static methods.

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Quick Revision

Override = child provides its own version of a parent method Rules: same name, same parameters, same or covariant return type Use @Override - it's your safety net against typos Runtime polymorphism: Java picks the method based on actual object type Cannot override private, static, or final methods

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Related Topics

• Method Overloading
• Polymorphism
• Abstraction
• Interfaces

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Next Lesson

08 - Method Overloading