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Ineheritance
Inheritance in Java
- Inheritance in Java is very simple and is
handled by the "extends" keyword. As you might expect,
subclasses work just like (inherit all of the functionality)
their superclass except that they typically add extra
funtionality.
| If a class does not specifically extend
anything then it will be automaticaly extended from the root
Object class |
- Thus, in the following example, we
create a subclass of Applet called myApplet:
public class myApplet extends Applet
{
...new fields and methods...
}
- Further, extension is transitive. That
is if you extend from a class which is an extension of another,
then you gain the functionality of your superclass as well as its
superclass.
- It is also worth noting that not only
can you add to the functionality of a superclass, but you can
modify existing functionality as well. This is achieved by
overriding the method in the subclass. To override a
superclass' method, you would implement your own method with the
same signature as your superclass' method. Thus, the Java
Virtual machine would use your implementation rather than your
superclass'. Of course, you can explicitly use your superclass'
methods and fields using the "super" keyword such as:
super.methodname();
- The super keyword is particularly
important when working with Constructors because subclasses do not
inherit the constructors of their superclasses. Thus, in order
to utilize the constructor of your superclass, you must explicitly
call it using the super keyword such as in the following example:
class myFrame extends Frame
{
public myFrame()
{
super();
}
public myFrame(String title)
{
super(title);
}
...the rest of your methods and fields....
}
| Java also provides the "final" keyword
which prevents a class from being subclassed, a method from
being overridden and a variable from changing its
initialized value. |
Additional Resources:
Operator Overloading (Polymorphism in Java)
Table of Contents
Packages
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