Java Reference
In-Depth Information
An anonymous class can be convenient where the class definition is short and simple. This technique
should not be used extensively as it tends to make the code very difficult to understand.
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 we 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 was 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 superclass. If two or
more subclasses, with a common base class, re-implement a common set of methods, these
methods can be selected for execution at run-time.
❑
A variable of a superclass can point to an object of any of its subclasses. Such a variable can
then be used to execute the subclass methods inherited from the superclass.
❑
A subclass of an abstract class must also be declared as
abstract
if it does not provide
definitions for all of the abstract methods inherited from its superclass.
❑
A class defined inside another class is called a nested class or inner class. An inner class may
itself contain inner classes.
❑
An interface can contain constants, abstract methods, and inner classes.
❑
A class can implement one or more interfaces by declaring them in the class definition, and
including the code to implement each of the interface methods.
❑
A class that does not define all the methods for an interface it implements must be declared
as
abstract
.
❑
