Source of CastingUpAndDown.java

Structures and functions

class A
class B
class CastingUpAndDown

  1: // CastingUpAndDown.java

  3: import java.io.*;

  5: class A
  6: {
  7:     protected int i = 2;
  8:     public A(){}
  9:     public int function()
 10:     {
 11:         return 2*i;
 12:     }
 13: }

 15: class B extends A
 16: {
 17:     protected int i = 3;
 18:     public B(){}
 19:     public int function()
 20:     {
 21:         return 3*i;
 22:     }
 23: }


 26: class CastingUpAndDown
 27: {
 28:     static PrintWriter screen = new PrintWriter(System.out, true);

 30:     static public void main(String[] args) throws IOException
 31:     {
 32:         A objectA;
 33:         B objectB = new B();

 35:         screen.println("\nValue of i from class B = " + objectB.i);
 36:         screen.println("Value of function from class B = " +
 37:                        objectB.function());

 39:         // Cast objectB to an instance of class A
 40:         objectA = (A)objectB;

 42:         screen.println("\nYou may refer to shadowed variables by " +
 43:                        "casting an object of the appropriate type:");
 44:         screen.println("Value of i from class A = " + objectA.i);
 45:         
 46:         screen.println("\nYou cannot refer to overriden methods by " +
 47:                        "casting an object to the appropriate type.");
 48:         screen.println("Value of function is still from class B = " +
 49:                        objectA.function() +"\n");
 50:     }
 51: }