How to sort two different objects in a collection?

Question

Suppose I have two classes CLassA and CLassB. And they have one atributte in common, for example the number of elements that each class holds.

How can i create a collect

Answer 1

Really ClassA and ClassB should be related either through an inheritance hierarchy, or by a common interface if you are going to put them both in the same collection.

The simplest thing would be to have a common interface that provides an accessor method for the common attribute. And then the comparator could use that method (through the interface) for fetching the value from ClassA's instance as well as ClassB's instance.