9.7 Object Superclass

Object Superclass

Learning Targets:

• What is the Object class
• Why is the Object class important to remember

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Every class and object created without the extends keyword will be implicitly extended from the Object Superclass. This means it will inherit some basic methods. Some notable methods are:

1. getClass()
2. toString()
3. equals()

So What?

Well its important to keep in mind when writing out your class. If you are planning to have a method in your class/object that matches the basic Object, then it must be a public override because all of the Object methods are public.

• are some methods from Object such as getClass() that you cannot override.

// this will return an error
class Shape {
    String toString(){
        return "Shape";
    }
}

// this will be fine
class Shape{
    @Override
    public String toString(){
        return "Shape";
    }
}

Popcorn Hacks

Create an example where you execute an unchanged method from Object, then execute a different method from Object that you changed.

class Vegetable {
    private String name;

    public Vegetable(String name) {
        this.name = name;
    }

    // Unchanged method from Object
    @Override
    public String toString() {
        return "Vegetable: " + name;
    }

    // Changed method from Object
    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true; // Check for reference equality
        if (obj == null || getClass() != obj.getClass()) return false; // Type check

        Vegetable vegetable = (Vegetable) obj;
        return name.equals(vegetable.name); // Compare names for equality
    }

    public static void main(String[] args) {
        Vegetable carrot = new Vegetable("Carrot");
        Vegetable anotherCarrot = new Vegetable("Carrot");
        Vegetable potato = new Vegetable("Potato");

        // Execute unchanged method
        System.out.println("Unchanged method (toString): " + carrot.toString());

        // Execute changed method
        System.out.println("Changed method (equals): " + carrot.equals(anotherCarrot)); // true
        System.out.println("Changed method (equals): " + carrot.equals(potato)); // false
    }
}

// Create an instance of Vegetable and call main method
Vegetable.main(null);

Unchanged method (toString): Vegetable: Carrot
Changed method (equals): true
Changed method (equals): false