[news.eclipse.platform.swt] problem about SWT drag and drop

["Shuai Yang" <yangshuai@xxxxxxxxx>]

hi everyone. i'm new to SWT. and i downloaded the source code of the book 
<<professional java native interfaces with swt jface>>. but the example 
program cannot run properly. any one can point out what's the point? Great 
thanks.

the code is
--------------------------------

/*******************************************************************************
 * All Right Reserved. Copyright (c) 1998, 2004 Jackwind Li Guojie
 *
 * Created on 2004-4-26 15:46:26 by JACK $Id$
 *
 ******************************************************************************/package com.asprise.books.javaui.ch16;import org.eclipse.swt.SWT;import org.eclipse.swt.dnd.DND;import org.eclipse.swt.dnd.DragSource;import org.eclipse.swt.dnd.DragSourceEvent;import org.eclipse.swt.dnd.DragSourceListener;import org.eclipse.swt.dnd.DropTarget;import org.eclipse.swt.dnd.DropTargetEvent;import org.eclipse.swt.dnd.DropTargetListener;import org.eclipse.swt.dnd.TextTransfer;import org.eclipse.swt.dnd.Transfer;import org.eclipse.swt.events.DisposeEvent;import org.eclipse.swt.events.DisposeListener;import org.eclipse.swt.graphics.Font;import org.eclipse.swt.widgets.Display;import org.eclipse.swt.widgets.Label;import org.eclipse.swt.widgets.MessageBox;import org.eclipse.swt.widgets.Shell;/** * */public class WordJumbles { Display display = new Display(); Shell shell = new Shell(display); String word; Label[] labelsRowOne; Label[] labelsRowTwo; Font font = new Font(display, "Arial", 18, SWT.BOLD); public void setDragSource(final Label label) {  // Allows text to be moved only.  int operations = DND.DROP_MOVE;  final DragSource dragSource = new DragSource(label, operations);  // Data should be transfered in plain text format.  Transfer[] formats = new Transfer[] { TextTransfer.getInstance()};  dragSource.setTransfer(formats);  dragSource.addDragListener(new DragSourceListener() {   public void dragStart(DragSourceEvent event) {    // Disallows drags if text is not available.    if (label.getText().length() == 0)     event.doit = false;   }   public void dragSetData(DragSourceEvent event) {    // Provides the text data.    if (TextTransfer.getInstance().isSupportedType(event.dataType))     event.data = label.getText();   }   public void dragFinished(DragSourceEvent event) {    // Removes the text after the move operation.    if (event.doit == true || event.detail == DND.DROP_MOVE) {     label.setText("");    }   }  });  label.addDisposeListener(new DisposeListener() {   public void widgetDisposed(DisposeEvent e) {    dragSource.dispose();   }  }); } public void setDropTarget(final Label label) {  int operations = DND.DROP_MOVE;  final DropTarget dropTarget = new DropTarget(label, operations);  // Data should be transfered in plain text format.  Transfer[] formats = new Transfer[] { TextTransfer.getInstance()};  dropTarget.setTransfer(formats);  dropTarget.addDropListener(new DropTargetListener() {   public void dragEnter(DropTargetEvent event) {    // Does not accept any drop if the label has text on it.    if(label.getText().length() != 0)     event.detail = DND.DROP_NONE;   }   public void dragLeave(DropTargetEvent event) {   }   public void dragOperationChanged(DropTargetEvent event) {   }   public void dragOver(DropTargetEvent event) {   }   public void drop(DropTargetEvent event) {    if (TextTransfer     .getInstance()     .isSupportedType(event.currentDataType)) {     String text = (String) event.data;     label.setText(text);     // Checks the result.     check();    }   }   public void dropAccept(DropTargetEvent event) {   }  });  label.addDisposeListener(new DisposeListener() {   public void widgetDisposed(DisposeEvent e) {    dropTarget.dispose();   }  }); } private void check() {  for(int i=0; i<word.length(); i++) {   if(! labelsRowTwo[i].getText().equals(word.charAt(i) + ""))    return;  }  MessageBox messageBox = new MessageBox(shell);  messageBox.setMessage("Success!");  messageBox.open(); } public WordJumbles(String word) {  this.word = word;  shell.setText("Word Jumbles");  labelsRowOne = new Label[word.length()];  labelsRowTwo = new Label[word.length()];  int width = 40;  // In the production version, you need to implement random permutation  // generation.  // Apache Jakarta Commons provides this function, see  // org.apache.commons.math.random.RandomDataImpl  int[] randomPermutation = { 5, 2, 6, 3, 1, 4, 0 };  for (int i = 0; i < word.length(); i++) {   final Label labelRowOne = new Label(shell, SWT.BORDER);   labelsRowOne[i] = labelRowOne;   labelRowOne.setBounds(10 + width * i, 10, width - 5, width - 5);   labelRowOne.setFont(font);   labelRowOne.setText(word.charAt(randomPermutation[i]) + "");   labelRowOne.setAlignment(SWT.CENTER);   setDragSource(labelRowOne);   //setDropTarget(labelRowOne);   final Label labelRowTwo = new Label(shell, SWT.BORDER);   labelsRowTwo[i] = labelRowTwo;   labelRowTwo.setBounds(    10 + width * i,    20 + width,    width - 5,    width - 5);   labelRowTwo.setBackground(display.getSystemColor(SWT.COLOR_WHITE));   labelRowTwo.setFont(font);   labelRowTwo.setAlignment(SWT.CENTER);   setDragSource(labelRowTwo);   //setDropTarget(labelRowTwo);  }  shell.pack();  shell.open();  //textUser.forceFocus();  // Set up the event loop.  while (!shell.isDisposed()) {   if (!display.readAndDispatch()) {    // If no more entries in event queue    display.sleep();   }  }  display.dispose(); } public static void main(String[] args) {  new WordJumbles("ECLIPSE"); }}