Why use Method Overriding in java

Question

I'm currently learning about Java and I encountered this particular function called method overriding. When do I need to override something from the parent class if I can just create a new function?

class Animal{
    boolean alive;
    void speak(){
        System.out.println("This animal speaks");
    }
}

class Dog extends Animal{
    @Override
    void speak(){
        System.out.println("The dog goes *bark*");
    }
}

why is there a need to override a method when I can just make a new method in the dog class?

class Dog extends Animal{
    void bark(){
        System.out.println("The dog goes *bark*");
    }
}

Answer 1

You override a method when you have a class hierarchy, as you do, where there is a sensible default behaviour which many of your subclasses will want to use, but some subclasses need different behaviour and you want to call the method using a reference of the base class.

If I had code like:

Dog d = new Dog();
d.speak();

Then just implementing bark() would be fine, because d is always a Dog. But when I have code like this:

Animal a;
if (...) {
 a = new Dog();
} else {
 a = new Cat();
}
a.speak();

Then we have to override a method. If the subclasses had a new method (like your bark()) which wasn't present on Animal we wouldn't be able to call it, because a is an Animal -- the actual object it refers to might be a Dog or a Cat.