overriding/poly morphic question

[Tosin Adedoyin]

class Light{
   protected String billtype = " small bill";
   protected double getbill( int nohours ){
      double smallAmount = 10.0,smallbill = smallAmount * nohours;
      System.out.println( billtype + " " + " " + smallbill );
      return smallbill;
   }
}
class Tube extends Light{
   protected String billtype = " Large  bill";
   public double getbill( final int nohours ){
      double LargeAmount = 100.0,largebill = LargeAmount * nohours;
      System.out.println( billtype + " " + " " + largebill );
      return largebill;
   }
   public double getbill(){
      System.out.println( "no bill" );
      return 0.0;
   }
   boolean test( Light L ){
      return true;
   }
   boolean test( Tube p ){
      return false;
   }
   public static void main( String args[] ){
      Tube t = new Tube();
      Light l1 = new Light();
      Light l2 = t;
      Light l3 = new Tube();
      System.out.println( l1.getClass() );
      System.out.println( l2.getClass() );
      System.out.println( l3.getClass() );
      t.getbill( 5 );
      l1.getbill( 5 );
      l2.getbill( 5 );
      l3.getbill( 5 );
      System.out.println( t.billtype );
      System.out.println( l1.billtype );
      System.out.println( l2.billtype );
      System.out.println( l3.billtype );
      System.out.println( t.test( l1 ) );
      // System.out.println(l3.test(l1));
   }
}

why does the comented line give me an error even though the class of l3 is tube why is it saying that it cannot find the test method in light . i thought it would use the one in tube
[ Jess Added UBB [CODE] tags to preserve whitespace, improve readibility ]
[ June 06, 2002: Message edited by: Jessica Sant ]

[Thiru Thangavelu]

Because l3 is a reference to a superclass Light which doesn't have a test method. To call test() like this it has to be overridden. Since it is not overridden and you want to call the method in the subclass a cast is definitly needed.
Hope this helps.

[Anna Dow]

Originally posted by Tosin Adedoyin:

class Light{
   protected String billtype = " small bill";
   protected double getbill( int nohours ){
      double smallAmount = 10.0,smallbill = smallAmount * nohours;
      System.out.println( billtype + " " + " " + smallbill );
      return smallbill;
   }
}
class Tube extends Light{
   protected String billtype = " Large  bill";
   public double getbill( final int nohours ){
      double LargeAmount = 100.0,largebill = LargeAmount * nohours;
      System.out.println( billtype + " " + " " + largebill );
      return largebill;
   }
   public double getbill(){
      System.out.println( "no bill" );
      return 0.0;
   }
   boolean test( Light L ){
      return true;
   }
   boolean test( Tube p ){
      return false;
   }
   public static void main( String args[] ){
      Tube t = new Tube();
      Light l1 = new Light();
      Light l2 = t;
      Light l3 = new Tube();
      System.out.println( l1.getClass() );
      System.out.println( l2.getClass() );
      System.out.println( l3.getClass() );
      t.getbill( 5 );
      l1.getbill( 5 );
      l2.getbill( 5 );
      l3.getbill( 5 );
      System.out.println( t.billtype );
      System.out.println( l1.billtype );
      System.out.println( l2.billtype );
      System.out.println( l3.billtype );
      System.out.println( t.test( l1 ) );
      // System.out.println(l3.test(l1));
   }
}

why does the comented line give me an error even though the class of l3 is tube why is it saying that it cannot find the test method in light . i thought it would use the one in tube
[ Jess Added UBB

 tags to preserve whitespace, improve readibility ]
[ June 06, 2002: Message edited by: Jessica Sant ][/quote]
Because you declare l3 as Light, so the compiler looks for test() method in Light class. You must use casting:
[CODE] 
System.out.println(((Light)l3).test(l1)); 

to avoid compiler errors

[Tosin Adedoyin]

thank you but i thought that when a method is invoked on an object using a reference , it is the class of the current object denoted by the reference not the type of the reference that determines which method implementation will be executed ? so i thought the method test in tube should be called becase l3 is of class Tube