Introduction
Inheritance
  Demo 1
Overriding
  Demo 2a   Demo 2b
this,super
MoreConstructors
  Demo 3
Abstraction
Interface 
  Demo 4
Casting References
MoreAboutArrays
Object class
Class Summary
Exercises

Perhaps you need to create a subclass to add new capabilities and so will override a method in the base class. However, you want to take advantage of code already in the overridden method rather than re-writing it in the overriding method.

You can obtain access to overriden methods and data with the super reference. In the following code, class B overrides a method in class A but calls the overridden method using the super reference:

public class A {   int i = 0;   void doSomething (){ i = 5;} } class B extends A {   int j = 0;   void doSomething () {     j = 10;     // Call the overridden method     super.doSomething ();     // And can use the shadowed     // property     j = j + i;   } }

You cannot cascade super references to access variables more than one class deep as in

   j = super.super.i; // error, not a valid use of super

This would seem logical but it is not allowed. Only the immediate superclass's data and methods can be accessed.

Note: Though one can override data variables (the overridden data is referred to as shadowed data), it is seldom useful and potentially very confusing.

We can also explicitly reference instance variables in the current object with the this reference. The code below illustrates a common technique to distinguish argument variables from instance or class variables:

Here the argument variables shadow the instance variables with the same variable names. However, the this reference explicitly indicates that the particular data names belong to the particular instance of the class.

Note: Do not confuse the this and super references with the this() and super() constructor invocations, which we discuss next.

            Tech
MoreComplexClass
ImprovedHistogram
JavaRandomNums
Vectors & Matrices
Exercises

           Physics
Runge-Kutta 2nd
  Demo 1
Runge-Kutta 4th
  Demo 2
BoundaryVal.Prob
Shooting Method
  Demo 3
Exercises