What's use of overriding and how can i use it??

Answer 1

Pls thoroughly read @Rrestoring explanation first!
A very simple example of a often overridden method is toString of Object, see
https://code.sololearn.com/c5pdVuw8Nmpe/?ref=app

Answer 2

This may not be the best explanation but I hope it helps!

Let's say I have a super class called Animal. I then have the sub classes, dog, cat, lion.
I then go about creating some objects, and each subclass counts how many objects I create in it.

I want to say the objects are equal if they have the same amount of created objects. However, the equals() method isn't defined for these kinds of objects.
So dog.equals(cat) doesn't make sense.

In this case I can override the equals() method.
By overriding it for all Animals, I'm letting the compiler know that I'm using Animals.equals, instead of String.equals for animal objects.

So I can do:
Animal a = new cat();
Animal b = new lion();
if(a.equals(b))
// same number of objects, therefore equal!

the equals method would look like this:
@Override
public boolean equals(Animal a){
return this.numObjects == a.numObjects;
}