This is a polymorphism assignment I can't seem to figure out for Java

Create an abstract class named Shapes. The Shapes class has only the calcArea() method.

From Shapes, create three derived classes named Circle, Square and RightTriangle.

Each of the three should have data members used to calculate the area of its shape. Define the method calcArea() for each of the three shapes. Each of the three shapes should also have appropriate constructors.

Not required, but create a class with the main() method to test the classes created above.

Submit: the source for all four (or five) classes.