That code on the top line will fail.  The problem is toArray not know
the type of the thing on the right, so all it can do is produce an
Object[] filled with MyClasses, which is a totally different animal
that a MyClass[] filled with MyClasses.  It can't be cast to
MyClass[].

If you give it a MyClass[] the right size to fill, or even an exemplar
empty MyClass[] array, then it knows the desired type of array.

The following analogous program will compile, but it fails with a
CastCastException on run.

import java.util.ArrayList;
public class CastExper
  {
  /**
   * test harness
   *
   * @param args not used
   */
  public static void main ( String[] args )
     {
     ArrayList a = new ArrayList(10);
     a.add( "elephant" );
     a.add( "beanbag" );
     String[] things = (String[])a.toArray();
     for ( String thing: things )
        {
        System.out.println( thing );
        }
     }
  }

This is how you would do it with generics

import java.util.ArrayList;
public class CastExper
  {
  /**
   * test harness
   *
   * @param args not used
   */
  public static void main ( String[] args )
     {
     ArrayList<String> a = new ArrayList<String>(10);
     a.add( "elephant" );
     a.add( "beanbag" );
     String[] things = a.toArray( new String[ a.size() ] );
     for ( String thing: things )
        {
        System.out.println( thing );
        }
     }
  }

The following code will not compile, even though you would think
toArray could, if it were written differently, might take advantage of
its knowledge that a was an ArrayList<String>. toArray() is defined
without any generics.  Because of type erasure, that knowledge is
useless in determining the actual return type.  The information  is
not around at run time to instantiate the precisely correct type of
array.

     String[] things = a.toArray();

With your help I've solved the problem. Thank you all!

k.w.wang