what i think is you have an intension of providing a body to abstract method,but it is not the definition of abstract method.so
in order to do so simply replace abstract with any other type or Override it in the extending class.and also please mention me what do you need to sort or more specifically about your problem.
Try to enjoy your work while doing it,it will Automatically convert in Hard Work...
I am afraid I don't understand the design of the app. You have got an abstract class and made it implement Comparable. That doesn't look quite right. Read this, which tells you that Comparable represents a total ordering and a natural order. That means that for every pair of instances of that class, you can hold your hand on your heart and say one of the following things:-
1: Object 1 is greater than object 2.
2: Object 1 is less than object 2.
3: Object 1 is the same as object 3.
I am not convinced you can do that with shapes. If you have a circle diameter 10, is it larger or smaller than a square with a diagonal 10? Does a circle have height and width? Does a circle have a diagonal?
By the way, there is a method in the Math class which calculates diagonals for you without your having to do all the arithmetic yourself.