An NPE is thrown when List.add() is called with a null item as the
argument. According to the spec, a null item is supposed to be treated
as an empty string, "".

/*
*/

/**
 * ListNullTest.java
 *
 * summary:
 */

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;


public class ListNullTest extends Applet
 {
   List list;

   public void init()
    {
      this.setLayout (new BorderLayout ());

      list = new List(15);
      //list.add("");
      //list.add(null);
      list.add("", 0);
      //list.add("", 1);
      list.add((String) null, 1);
      System.out.println("Just added the null item");

      this.add("South", list);
      System.out.println("Just added the list");

      String[] instructions =
       {
         " This test program adds two items to a List: one with \"\" as the ",
         " item and one with null as the item. It then checks to see if the ",
         " List really handles the null item as \"\".",
         " ",
         " Instructions:",
         " ",
         " If no null pointer exception was thrown, the test passed. "
       };

      Sysout.createDialogWithInstructions( instructions );

    }//End init()

   public void start ()
    {
      setSize (200,300);
      setVisible(true);

    }// start()

 }// class ListAddPerfTest


  
/****************************************************
 Standard Test Machinery
 DO NOT modify anything below -- it's a standard
  chunk of code whose purpose is to make user
  interaction uniform, and thereby make it simpler
  to read and understand someone else's test.
 ****************************************************/

/**
 This is part of the standard test machinery.
 It creates a dialog (with the instructions), and is the interface
  for sending text messages to the user.
 To print the instructions, send an array of strings to Sysout.createDialog
  WithInstructions method. Put one line of instructions per array entry.
 To display a message for the tester to see, simply call Sysout.println
  with the string to be displayed.
 This mimics System.out.println but works within the test harness as well
  as standalone.
 */

class Sysout
 {
   private static TestDialog dialog;

   public static void createDialogWithInstructions( String[] instructions )
    {
      dialog = new TestDialog( new Frame(), "Instructions" );
      dialog.printInstructions( instructions );
      dialog.show();
      println( "Any messages for the tester will display here." );
    }
   
   public static void createDialog( )
    {
      dialog = new TestDialog( new Frame(), "Instructions" );
      String[] defInstr = { "Instructions will appear here. ", "" } ;
      dialog.printInstructions( defInstr );
      dialog.show();
      println( "Any messages for the tester will display here." );
    }
   
      
   public static void printInstructions( String[] instructions )
    {
      dialog.printInstructions( instructions );
    }


   public static void println( String messageIn )
    {
      dialog.displayMessage( messageIn );
    }

 }// Sysout class

/**
  This is part of the standard test machinery. It provides a place for the
   test instructions to be displayed, and a place for interactive messages
   to the user to be displayed.
  To have the test instructions displayed, see Sysout.
  To have a message to the user be displayed, see Sysout.
  Do not call anything in this dialog directly.
  */
class TestDialog extends Dialog
 {

   TextArea instructionsText;
   TextArea messageText;
   int maxStringLength = 80;
   
   //DO NOT call this directly, go through Sysout
   public TestDialog( Frame frame, String name )
    {
      super( frame, name );
      int scrollBoth = TextArea.SCROLLBARS_BOTH;
      instructionsText = new TextArea( "", 15, maxStringLength, scrollBoth );
      add( "North", instructionsText );
      
      messageText = new TextArea( "", 5, maxStringLength, scrollBoth );
      add("South", messageText);
      
      pack();
      show();
    }// TestDialog()

   //DO NOT call this directly, go through Sysout
   public void printInstructions( String[] instructions )
    {
      //Clear out any current instructions
      instructionsText.setText( "" );

      //Go down array of instruction strings

      String printStr, remainingStr;
      for( int i=0; i < instructions.length; i++ )
       {
         //chop up each into pieces maxSringLength long
         remainingStr = instructions[ i ];
         while( remainingStr.length() > 0 )
          {
            //if longer than max then chop off first max chars to print
            if( remainingStr.length() >= maxStringLength )
             {
               //Try to chop on a word boundary
               int posOfSpace = remainingStr.
                  lastIndexOf( ' ', maxStringLength - 1 );
               
               if( posOfSpace <= 0 ) posOfSpace = maxStringLength - 1;
                              
               printStr = remainingStr.substring( 0, posOfSpace + 1 );
               remainingStr = remainingStr.substring( posOfSpace + 1 );
             }
            //else just print
            else
             {
               printStr = remainingStr;
               remainingStr = "";
             }
            
            instructionsText.append( printStr + "\n" );
            
          }// while
         
       }// for
      
    }//printInstructions()

   //DO NOT call this directly, go through Sysout
   public void displayMessage( String messageIn )
    {
      messageText.append( messageIn + "\n" );
    }
   
 }// TestDialog class