General Java Questions I

returns an Enumeration will actually be returning an inner class that implements

Enumeration

(and therefore defining hasMoreElements and nextElement in a manner that is

specific to traversing a Hashtable). 

If this doesn t help, maybe you could clear up what you mean by Enumeration having

defined methods.

Eric

 Q: can anyone provide an example on how to use clone() and clonable interface?

Answer:

//Class Point uses default clone implementation that returns

//shallow copy of Point (which is sufficient in this case).

class Point implements Cloneable {

     int x, y;

}

class ImmutableRectangle {

   private Point lowerLeft = new Point();

   private Point upperRight = new Point();

   public Point getLowerLeftPoint() {

      try {

         return lowerLeft.clone();

      }

      catch(CloneNotSupportedException e) {

            //shouldn t occur since Point is cloneable

            throw new InternalError();

     }

   }

}

we don t want Rectangle points to be changed outside its class. the best

way would be to create a copy of Point object and pass it.

i5mast

MVP for Java 2

http://www.brainbench.com

 Q: Why does not switch work properly?

From Thinking In Java, chapter 7, Shapes.java:

// ...

switch((int)(Math.random() * 3)) {

   default:

   case 0: return new Circle();

   case 1: return new Square();

   case 2: return new Triangle();

}

// ...

How does this switch work??? why is default preceding all other cases? 

What I think, this should always return case 0, but still, it properly

file:///F|/a_jsite/350_tips/general_java I.htm (23 of 33) [2001 07 08 11:24:51]