What do you mean by "show polymorphism"? In Java, all instance methods are polymorphic.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus
You can infer polymorphism in places. When you see B inherit from A or implement interface A, you get a strong clue hint polymorphic behavior is desired. When you see a parameter declared as A and then look in the class hierarchy and see a number of classes inherit from A or implement A, same thing.
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi