Java Method Overriding

1. What Is Method Overriding?

Method overriding happens when a child class creates its own version of a method that already exists in the parent class.

Simple Definition: Method overriding allows a subclass to replace or customize a method from its superclass.

2. Why Do We Use Method Overriding?

Programmers use method overriding when different objects should perform the same action in different ways.

For example, a general Animal class may have a method called makeSound().

Different animals make different sounds:

• A dog barks.
• A cat meows.
• A cow moos.

Each animal can override the makeSound() method with its own version.

3. Parent Class Example

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

This class has a method called makeSound().

4. Child Class Overriding the Method

public class Dog extends Animal
{
    @Override
    public void makeSound()
    {
        System.out.println("The dog barks.");
    }
}

The Dog class extends Animal.

The Dog class overrides the makeSound() method.

5. Driver Class Example

public class AnimalDriver
{
    public static void main(String[] args)
    {
        Animal myAnimal = new Animal();
        Dog myDog = new Dog();

        myAnimal.makeSound();
        myDog.makeSound();
    }
}

Output

The animal makes a sound.
The dog barks.

6. Important Rules for Overriding

To override a method, the child class method must have:

1. The same method name
2. The same return type
3. The same parameter list
4. A relationship using inheritance

public void makeSound()

7. The @Override Annotation

The @Override annotation tells Java that you are trying to override a method.

@Override
public void makeSound()
{
    System.out.println("The dog barks.");
}

Why Use @Override?

It helps Java catch mistakes.

@Override
public void makesound()
{
    System.out.println("The dog barks.");
}

This would cause an error because makesound() does not match makeSound().

8. Example With Multiple Child Classes

Parent Class

public class Vehicle
{
    public void move()
    {
        System.out.println("The vehicle moves.");
    }
}

Child Class 1

public class Car extends Vehicle
{
    @Override
    public void move()
    {
        System.out.println("The car drives on the road.");
    }
}

Child Class 2

public class Boat extends Vehicle
{
    @Override
    public void move()
    {
        System.out.println("The boat moves through the water.");
    }
}

Child Class 3

public class Airplane extends Vehicle
{
    @Override
    public void move()
    {
        System.out.println("The airplane flies in the sky.");
    }
}

Driver Class

public class VehicleDriver
{
    public static void main(String[] args)
    {
        Vehicle vehicle = new Vehicle();
        Car car = new Car();
        Boat boat = new Boat();
        Airplane airplane = new Airplane();

        vehicle.move();
        car.move();
        boat.move();
        airplane.move();
    }
}

Output

The vehicle moves.
The car drives on the road.
The boat moves through the water.
The airplane flies in the sky.

9. Method Overriding and Inheritance

Method overriding only works when inheritance is involved.

Inheritance uses the keyword:

extends

Example:

public class Dog extends Animal

This means:

• Dog is a child class of Animal.
• Dog inherits from Animal.
• Dog can override methods from Animal.

10. Overriding vs. Overloading

Method Overriding Example

public class Parent
{
    public void sayHello()
    {
        System.out.println("Hello from the parent class.");
    }
}

public class Child extends Parent
{
    @Override
    public void sayHello()
    {
        System.out.println("Hello from the child class.");
    }
}

Method Overloading Example

public class Calculator
{
    public int add(int a, int b)
    {
        return a + b;
    }

    public int add(int a, int b, int c)
    {
        return a + b + c;
    }
}

11. Using super With Overriding

Sometimes, a child class may want to use the parent class version of a method.

To do this, use:

super.methodName();

Example

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

public class Dog extends Animal
{
    @Override
    public void makeSound()
    {
        super.makeSound();
        System.out.println("The dog barks.");
    }
}

Driver

public class DogDriver
{
    public static void main(String[] args)
    {
        Dog dog = new Dog();
        dog.makeSound();
    }
}

Output

The animal makes a sound.
The dog barks.

12. Real-World Example

Think about a school.

A general Person class may have a method called work().

public class Person
{
    public void work()
    {
        System.out.println("The person does work.");
    }
}

A Teacher works differently from a Student.

public class Teacher extends Person
{
    @Override
    public void work()
    {
        System.out.println("The teacher teaches students.");
    }
}

public class Student extends Person

{
    @Override
    public void work()
    {
        System.out.println("The student completes assignments.");
    }
}

13. Complete Program Example

File 1: Person.java

public class Person
{
    public void work()
    {
        System.out.println("The person does work.");
    }
}

File 2: Teacher.java

public class Teacher extends Person
{
    @Override
    public void work()
    {
        System.out.println("The teacher teaches a lesson.");
    }
}

File 3: Student.java

public class Student extends Person
{
    @Override
    public void work()
    {
        System.out.println("The student completes classwork.");
    }
}

File 4: PersonDriver.java

public class PersonDriver
{
    public static void main(String[] args)
    {
        Person person = new Person();
        Teacher teacher = new Teacher();
        Student student = new Student();

        person.work();
        teacher.work();
        student.work();
    }
}

Output

The person does work.
The teacher teaches a lesson.
The student completes classwork.

14. Common Student Mistakes

// Incorrect
public void MakeSound()

// Correct
public void makeSound()

// Parent method
public void move()

// Incorrect child method for overriding
public void move(String direction)

// Incorrect
public class Dog

// Correct
public class Dog extends Animal

// Incorrect
public void makeSound

// Correct
public void makeSound()

15. Key Vocabulary

16. Check for Understanding

Question 1

What is method overriding?

Answer: Method overriding is when a child class creates its own version of a method that already exists in the parent class.

Question 2

What keyword is used for inheritance in Java?

Answer: extends

Question 3

What annotation is commonly used when overriding a method?

Answer: @Override

Question 4

Can a method be overridden without inheritance?

Answer: No. Method overriding requires inheritance.

Question 5

What does super.methodName() do?

Answer: It calls the parent class version of the method.

17. Summary

Main Idea

Same method name.
Same parameters.
Different behavior in the child class.