Abstract classes are made to implemnt the java concept of abstractio n which is useful to hide the actually implemention of the data.Like if we have a animal class and its method is eat.If canine and veg class extends Animal then canine will override eat as meat and veg will have grass.There is no point of making an object out of Animal,so we have to make it abstract class.Any non-abstrct class which extends abstract calss have to implement the abstrct method in it.it's like a protocol we have follow.