Why do we need abstract methods?

Question

I have been studying abstract methods lately and I can't understand why do we need them? I mean, after all, we are just overriding them. Do you know its just a declaration? Why do we need them?

Also, I tried understanding this from the internet and everywhere there's an explanation like imagine there's an abstract class human then there're its subclasses disabled and not disabled then the abstract function in human class walking() will contain different body or code. Now what I am saying is why don't we just create a function in the disabled and not disabled subclasses instead of overriding. Thus again back to the question in the first paragraph. Please explain it.

Answer 1

One of the most obvious uses of abstract methods is letting the abstract class call them from an implementation of other methods.

Here is an example:

class AbstractToy {
    protected abstract String getName();
    protected abstract String getSize();
    public String getDescription() {
        return "This is a really "+getSize()+" "+getName();
    }
}
class ToyBear extends AbstractToy {
    protected override String getName() { return "bear"; }
    protected override String getSize() { return "big"; }
}
class ToyPenguin extends AbstractToy {
    protected override String getName() { return "penguin"; }
    protected override String getSize() { return "tiny"; }
}

Note how AbstractToy's implementation of getDescription is able to call getName and getSize, even though the definitions are in the subclasses. This is an instance of a well-known design pattern called Template Method.