General Java Questions III

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

returns random cases in the range 0..2.

Answer: Don t assume that just because default is first in the code, that it will match

first. In fact the default is only used when there is no matching case, as you have

discovered.

file:///F|/a_jsite/350_tips/general_java III.htm (8 of 9) [2001 07 08 11:24:53]