Java Method Overriding & super Keyword

1. Overview

2. Understanding Method Overriding

When an overridden method is called using a superclass reference pointing to a child object, Java decides which method to run at runtime based on the actual object type.

class Animal {
    void makeSound() {
        System.out.println("Generic animal sound");
    }
}

class Dog extends Animal {
    @Override // Ensures correct signature
    void makeSound() {
        System.out.println("Bark! Bark!");
    }
}

// Usage:
Animal myPet = new Dog(); 
myPet.makeSound(); // Output: Bark! Bark! (Runtime Polymorphism)

3. The 3 Key Uses of the super Keyword

The super keyword bridges the gap between child logic and parent logic.

class Vehicle {
    int maxSpeed = 120;

    Vehicle(String type) {
        System.out.println("Vehicle Constructor: " + type);
    }

    void start() {
        System.out.println("Vehicle is starting...");
    }
}

class Car extends Vehicle {
    int maxSpeed = 200; // Hides parent maxSpeed

    Car() {
        super("Four-Wheeler"); // 1. Calls Parent Constructor (MUST be first line!)
    }

    @Override
    void start() {
        super.start(); // 2. Calls Parent Method
        System.out.println("Car engine roaring!");
    }

    void showSpeeds() {
        System.out.println("Car speed: " + maxSpeed);       // 200
        System.out.println("Vehicle speed: " + super.maxSpeed); // 3. Accesses Parent Variable (120)
    }
}

4. Interactive Execution Explorer

Click through the tabs below to simulate how method overriding and super operate in real Java scenarios.

Animal a = new Cat();
a.sound(); // Calls Cat's sound() method at runtime

class Employee {
    void work() { System.out.println("Working on general tasks..."); }
}
class Developer extends Employee {
    @Override
    void work() {
        super.work(); // Execute base logic first
        System.out.println("Writing Java Code!");
    }
}

class Person {
    Person(String name) { System.out.println("Person name: " + name); }
}
class Student extends Person {
    Student(String name, int id) {
        super(name); // Passes name to Person constructor
        System.out.println("Student ID: " + id);
    }
}

5. Rules & Constraints Matrix