What are abstract classes and abstract methods? [duplicate]

Answer 1

abstract method do not have body.A well defined method can't be declared abstract.

A class which has abstract method must be declared as abstract.

Abstract class can't be instantiated.

Answer 2

Once you get what abstract means in Java, you would ask: why they put this in ? Java may work without abstract stuff, BUT it makes part of a certain OO style or vocabulary. There exists really situations where an abstract class or method is an elegant way to express the program authors intention. Most when you are programming a framework or a library that will be used by others.