Ivor Horton's Beginning Java™ 2, JDK™ 5th Edition

6.15. Summary

You should now understand polymorphism and how to apply it. You will find that this technique can be utilized to considerable advantage in the majority of your Java programs. It will certainly appear in many of the examples in the remaining chapters.

The important points I have covered in this chapter are:

• An abstract method is a method that has no body defined for it and is declared using the keyword abstract.

• An abstract class is a class that contains one or more abstract methods. It must be defined with the attribute abstract.

• You can define one class based on another. This is called class derivation or inheritance. The base class is called a superclass, and the derived class is called a subclass. A superclass can also be a subclass of another superclass.

• A subclass inherits certain members of its superclass. An inherited member of a class can be referenced and used as though it were declared as a normal member of the class.

• A subclass does not inherit the superclass constructors.

• The private members of a superclass are not inherited in a subclass. If the subclass is not in the same package as the superclass, then members of the superclass that do not have an access attribute are not inherited.

• The first statement in the body of a constructor for a subclass should call a constructor for the superclass. If it does not, the compiler will insert a call for the default constructor for the superclass.

• A subclass can re-implement, or overload, the methods inherited from its ...