Java Tutorial/SWT/SWT Basics

Coding Your First SWT Program: Hello World

import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class SWTFirst {
  public static void main(String[] args) {
    Display display = new Display();
    Shell shell = new Shell(display);
    shell.setText("Hello, world!");
    shell.open();
    // Set up the event loop.
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        // If no more entries in the event queue
        display.sleep();
      }
    }
    display.dispose();
  }
}

Operating System Resources

Operating system resources in SWT refer to native resources used by those (operating system) resourcebased objects, e.g. Display, Color, Font, GC, Image, Printer, Region, and Widgets. Most of the classes in the following packages are resource-based:

org.eclipse.swt.custom
org.eclipse.swt.graphics
org.eclipse.swt.widgets

You can check whether a class has a dispose() method. If it does, then it is very likely resource-based. Otherwise, it isn"t.

SWT useful utilities

/*
 * (c) Copyright 2004 by Heng Yuan
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * ITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */
package cookxml.cookswt.util;
import java.util.HashMap;
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;
/**
 * SWT useful utilities.
 *
 * @since CookSwt 1.0
 * @author Heng Yuan
 */
public class SwtUtils
{
  /**
   * automatically dispose Color resource
   */
  public static boolean autoDisposeColor = true;
  /**
   * automatically dispose Font resource
   */
  public static boolean autoDisposeFont = true;
  /**
   * automatically dispose Image resource
   */
  public static boolean autoDisposeImage = true;
  /**
   * automatically dispose Image resource
   */
  public static boolean autoDisposeCursor = true;
  /**
   * This is a table of system colors that cannot be disposed.
   */
  private static HashMap s_systemColorTable;
  /**
   * This is a table of system cursors that cannot be disposed.
   */
  private static HashMap s_systemCursorTable;
  /**
   * This is a table of system images that cannot be disposed.
   */
  private static HashMap s_systemImageTable;
  /**
   * Setup the system color table for the given device.
   *
   * @param  device the display device.
   */
  private static void setupSystemColorTable (Device device)
  {
    HashMap colorTable = new HashMap ();
    for (int i = 0; i <= 35; ++i)
    {
      Color c = device.getSystemColor (i);
      colorTable.put (c, c);
    }
    s_systemColorTable = colorTable;
  }
  /**
   * Setup the system cursor table for the given device.
   *
   * @param  display the display device.
   */
  private static void setupSystemCursorTable (Display display)
  {
    HashMap cursorTable = new HashMap ();
    for (int i = 0; i <= 21; ++i)
    {
      Cursor c = display.getSystemCursor (i);
      cursorTable.put (c, c);
    }
    s_systemCursorTable = cursorTable;
  }
  /**
   * Setup the system cursor table for the given device.
   *
   * @param  display the display device.
   */
  private static void setupSystemImageTable (Display display)
  {
    HashMap imageTable = new HashMap ();
    Image image;
    image = display.getSystemImage (SWT.ICON_ERROR);
    imageTable.put (image, image);
    image = display.getSystemImage (SWT.ICON_INFORMATION);
    imageTable.put (image, image);
    image = display.getSystemImage (SWT.ICON_QUESTION);
    imageTable.put (image, image);
    image = display.getSystemImage (SWT.ICON_WARNING);
    imageTable.put (image, image);
    image = display.getSystemImage (SWT.ICON_WORKING);
    imageTable.put (image, image);
    s_systemImageTable = imageTable;
  }
  /**
   * Check if a color is a system color.  A system color cannot be disposed.
   *
   * @param  color The color to be disposed.
   * @param  device The device that contains the color.
   */
  public static boolean isSystemColor (Color color, Device device)
  {
    if (s_systemColorTable == null)
      setupSystemColorTable (device);
    return s_systemColorTable.get (color) == color;
  }
  /**
   * Check if a color is a system color.  A system color cannot be disposed.
   *
   * @param  cursor The cursor to be disposed.
   * @param  display The display device.
   */
  public static boolean isSystemCursor (Cursor cursor, Display display)
  {
    if (s_systemCursorTable == null)
      setupSystemCursorTable (display);
    return s_systemCursorTable.get (cursor) == cursor;
  }
  /**
   * Check if a color is a system color.  A system color cannot be disposed.
   *
   * @param  image The image to be disposed.
   * @param  display The display device.
   */
  public static boolean isSystemImage (Image image, Display display)
  {
    if (s_systemImageTable == null)
      setupSystemImageTable (display);
    return s_systemImageTable.get (image) == image;
  }
  /**
   * Check if a color is a system color.  A system color cannot be disposed.
   *
   * @param  font The font to be disposed.
   * @param  device The display device.
   */
  public static boolean isSystemFont (Font font, Device device)
  {
    return device.getSystemFont () == font;
  }
  /**
   * Dispose a color if it is not a system color.
   *
   * @param  color The color to be disposed.
   * @param  device The device that contains the color.
   */
  public static void disposeColor (Color color, Device device)
  {
    if (color.isDisposed ())
      return;
    if (!isSystemColor (color, device))
    {
      assert disposeDebug ("Dispose color: " + color);
      color.dispose ();
    }
  }
  /**
   * Dispose a color if it is not a system color.
   *
   * @param  image The image to be disposed.
   * @param  device The device that contains the color.
   */
  public static void disposeImage (Image image, Display device)
  {
    if (image.isDisposed ())
      return;
    if (!isSystemImage (image, device))
    {
      assert disposeDebug ("Dispose image: " + image);
      image.dispose ();
    }
  }
  /**
   * Attach a DisposeListener that dispose the resource when the widget
   * object is disposed.
   *
   * @param  widget the widget to listen to.
   * @param  color the resource to be disposed.
   */
  public static void attachColorDisposeListener (Widget widget, Color color)
  {
    if (autoDisposeColor &&
      !isSystemColor (color, widget.getDisplay ()))
      widget.addDisposeListener (new ColorDisposeListener (color));
  }
  /**
   * Attach a DisposeListener that dispose the resource when the widget
   * object is disposed.
   *
   * @param  widget the widget to listen to.
   * @param  cursor the resource to be disposed.
   */
  public static void attachCursorDisposeListener (Widget widget, Cursor cursor)
  {
    if (autoDisposeCursor &&
      !isSystemCursor (cursor, widget.getDisplay ()))
      widget.addDisposeListener (new CursorDisposeListener (cursor));
  }
  /**
   * Attach a DisposeListener that dispose the resource when the widget
   * object is disposed.
   *
   * @param  widget the widget to listen to.
   * @param  font the resource to be disposed.
   */
  public static void attachFontDisposeListener (Widget widget, Font font)
  {
    if (autoDisposeFont &&
      !isSystemFont (font, widget.getDisplay ()))
      widget.addDisposeListener (new FontDisposeListener (font));
  }
  /**
   * Attach a DisposeListener that dispose the resource when the widget
   * object is disposed.
   *
   * @param  widget the widget to listen to.
   * @param  image the resource to be disposed.
   */
  public static void attachImageDisposeListener (Widget widget, Image image)
  {
    if (autoDisposeImage &&
       !isSystemImage (image, widget.getDisplay ()))
      widget.addDisposeListener (new ImageDisposeListener (image));
  }
  /**
   * Attach a dropdown menu to a drop down ToolItem.  The drop down menu will be
   * automatically positioned and displayed at under the ToolItem.
   *
   * @param  item the drop down tool item
   * @param  menu the drop down menu
   */
  public static void attachToolItemDropDownMenu (ToolItem item, Menu menu)
  {
    item.addSelectionListener (new DropDownListener (menu));
  }
  /**
   * Open all the shells inside the Display object and dispose the Display
   * after all shells are disposed.
   *
   * @param display the Display object.
   */
  public static void showDisplay (Display display)
  {
    // open shells for display
    Shell[] shells = display.getShells ();
    for (int i = 0; i < shells.length; ++i)
    {
      if (!shells[i].isDisposed () && !shells[i].isVisible ())
        shells[i].open ();
    }
    // exit after all shells are disposed
    while (!display.isDisposed ())
    {
      shells = display.getShells ();
      boolean canExit = true;
      for (int i = 0; i < shells.length; ++i)
      {
        if (!shells[i].isDisposed ())
        {
          canExit = false;
          break;
        }
      }
      if (canExit)
        break;
      if (!display.readAndDispatch ())
        display.sleep ();
    }
    if (!display.isDisposed ())
      display.dispose ();
  }
  /**
   * This function is supposed to work in conjunction with assert to generate
   * a debug message but does not really throw an Exception
   *
   * @param  msg the message to be printed.
   * @return  true
   */
  public static boolean disposeDebug (String msg)
  {
    System.out.println (msg);
    return true;
  }
}

The SWT Class-Constants and Methods

The SWT class contains a repository of class-level constants and methods to simplify SWT programming.

import org.eclipse.swt.SWT;
public class UsingSWTGettingPaltFormVersion {
  public static void main(String[] args) {
    System.out.println(SWT.getPlatform());
    System.out.println(SWT.getVersion());
  }
}

win32
3138

Two simple rules to guide your disposal efforts

1. If you created it, you dispose it.
2. Disposing the parent disposes the children.

(from Carolyn MacLeod and Steve Northover)