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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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<article id="article">
	<articleinfo>
		<title>Swing/SWT Integration</title>
		<releaseinfo role="SVN"> $Id: article.xml,v 1.3 2007/06/20 15:33:53 wbeaton Exp $ </releaseinfo>
		<date>June 20, 2007</date>
		<authorgroup>
		  <author>
		    <firstname>Gordon</firstname>
		    <surname>Hirsch</surname>
		    <affiliation>
		      <orgname>SAS Institute Inc.</orgname>
		    </affiliation>
		  </author>
		</authorgroup>
		<copyright>
			<year>2007</year>
			<holder>SAS Institute Inc. Made available under the EPL v1.0 </holder>
		</copyright>
		<abstract>
			<para>
             Swing and SWT are sometimes seen as strictly competing technologies. Some 
             people have strong opinions on which UI toolkit to use exclusively for client
             applications. However, in the real world, ideological extremes are
             often impractical. Some valid use cases require both technologies
             to coexist in a single application. While mixing the two toolkits is not a
             simple task, it can be done, and it can be done such that the two toolkits
             are smoothly integrated. This article discusses the steps necessary to
             achieve good Swing/SWT integration. It focuses on the use case of embedding
             existing Swing components into an SWT-based Rich Client Platform application.
			</para>
		</abstract>
        <legalnotice>
          <para>Java and all Java-based trademarks are trademarks of Sun Microsystems, Inc. in
            the United States, other countries, or both.</para>
          <para>Other company, product, or service names may be trademarks or service marks of
            others.</para>
        </legalnotice>
	</articleinfo>
	<section id="sec-introduction">
		<title>Introduction</title>
    
		<para>
		  Many existing standalone Java clients represent a large investment in Swing
		  components. While there are compelling arguments for moving these clients to the Eclipse Rich
		  Client Platform (RCP), the full migration of a large existing application can be
		  expensive. By retaining some Swing components, the initial cost of 
          migration can be reduced. Over time, Swing components may be incrementally converted
          to SWT if and when it becomes necessary. 
		</para>
        <para>
          For example, at SAS we have extended the standard Swing <ulink url="http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/JTable.html">
          <code>JTable</code></ulink> component to
          create an enhanced table that meets the needs of our existing applications. 
          A large effort will be required to convert this component to SWT. Instead of 
          waiting for an equivalent SWT table, we are able to use the Swing
          table component as-is in an RCP application, as shown in the screenshot below. 
          It shows an RCP application running on the Windows XP platform. 
          The two tables are Swing components; all other components
          were created with SWT.
        </para>
        <figure id="fig-table-embed">
          <title>Embedding Swing Table Components</title>
          <mediaobject>
            <imageobject>
              <imagedata fileref="images/table-embed.png"/>
            </imageobject>
          </mediaobject>
        </figure>
        <para>
          We also have a large inventory of complex Swing components to display graphs and charts. 
          Again, by mixing Swing and SWT, we can consider the conversion of these Swing components separately from 
          the immediate needs of an application that we'd like to migrate to RCP. 
          The screenshot below shows another RCP application with a Swing-based graph 
          component. Everything else in the image is an
          SWT component. (This application may not look like an RCP application, 
          but it is. The unusual look is due to extensive use of the Eclipse 
          presentations API and other advanced workbench features.)
        </para>
        <figure id="fig-graph-embed">
          <title>Embedding Graphical Swing Components</title>
          <mediaobject>
            <imageobject>
              <imagedata fileref="images/graph-embed.jpg"/>
            </imageobject>
          </mediaobject>
        </figure>
		<para>
		  The use of Swing components with the RCP implies that two large UI toolkits will coexist in a
		  single application and that some amount of integration is necessary to ensure UI
		  consistency across the entire application.
		</para>
		<para>
		  SWT provides the SWT/AWT Bridge <xref linkend="bib-bridge"/> as the basic infrastructure for Swing/SWT integration.
          However, the bridge is only the first step along the
		  path to embedding usable Swing components in RCP applications. Much of
		  this article is devoted to explaining the additional practices necessary for 
          effective integration. Without these practices, the
		  SWT/AWT Bridge is insufficient for production-quality application use.
		  With them, you can successfully host key Swing components in RCP
		  applications.
		</para>
        <para>
          Integrating two independent UI toolkits is a complicated task, and it
          rarely produces perfect results. This article 
          concentrates on practical techniques (and yes, even some hacks) to make the 
          integration effective enough for use in real-world applications. 
        </para>
		<para>
		  Despite the complexity, most of the practices described below can be encapsulated 
          in a single common base class to be used when embedding Swing components. There are additional 
          helper classes to support the implementation. An example is included with this
          article. See <xref linkend="app-example-code"/> for more information. 
		</para>
	</section>
	<section id="sec-using-bridge">
	  <title>Using the SWT/AWT Bridge</title>
	  <para>
	    The SWT/AWT Bridge has been part of SWT since version 3.0. It is
	    a very simple API, located in the package
        <code>
	    <ulink
	      url="http://help.eclipse.org/help32/topic/org.eclipse.platform.doc.isv/reference/api/org/eclipse/swt/awt/package-summary.html">
	      org.eclipse.swt.awt</ulink>.
        </code>
	  </para>
      <note>
        <para>
          This article focuses on embedding AWT frames inside SWT composites. It demonstrates only
          one half of the SWT/AWT Bridge. Nevertheless, most of the improvements described below also apply to the
          other direction: embedding SWT composites inside AWT frames.
        </para>
      </note>
	  <para>Minimally, embedding an AWT frame inside an SWT composite is just two simple lines of code</para>
      <programlisting>
    Composite composite = new Composite(parent, SWT.EMBEDDED | SWT.NO_BACKGROUND);
    Frame frame = SWT_AWT.new_Frame(composite);
      </programlisting>
      <para>
        An instance of <code>org.eclipse.swt.Composite</code> is created with the <code>SWT.EMBEDDED</code> 
        style. This style signals that an AWT frame is to be embedded inside the Composite. The call to the static <code>new_Frame</code>
        method creates and returns such a frame. The frame may then be
        populated with AWT and/or Swing components. 
      </para>
      <para>
        The returned frame is not a standard AWT frame. By default, it is a subclass of <code>java.awt.Frame</code>
        that is meant to be embedded within native applications. In fact, it is the same frame that is used to 
        embed <ulink url="http://java.sun.com/applets/">applets</ulink> inside a browser window. 
      </para>
      <para>
        The example code shown above is deceptively simple. While SWT does much under the covers to manage the 
        integration of the two toolkits, the scope of the bridge's implementation is very narrow. In reality, you must do much
        more in your application to make the integration more consistent. These additional steps are 
        described below in <xref linkend="sec-adding-to-bridge"/>.
      </para>
      <section id="sec-platform">
        <title>Platform Considerations</title>
        <para>
          There are version constraints for using the SWT/AWT Bridge that differ from platform to
          platform.
        </para>
        <table id="version-table" frame='all'>
          <title>Minimum Versions</title>
          <tgroup cols='3' align='left' colsep='1' rowsep='1'>
            <colspec colname='c1' />
            <colspec colname='c2' />
            <colspec colname='c3' />
            <thead>
              <row>
                <entry>Platform</entry>
                <entry>JRE Version</entry>
                <entry>Eclipse Version</entry>
              </row>
            </thead>
            <tbody>
              <row>
                <entry>Windows</entry>
                <entry>1.4</entry>
                <entry>3.0</entry>
              </row>
              <row>
                <entry>Linux/GTK</entry>
                <entry>1.5</entry>
                <entry>3.0</entry>
              </row>
              <row>
                <entry>Mac OS X</entry>
                <entry>1.5.0 Release 4</entry>
                <entry>3.2</entry>
              </row>
            </tbody>
          </tgroup>
        </table>
        <note>
          <para>
            Mac OS X also requires installation of the SWT Compatibility
            Libraries. See the SWT
            <ulink url="http://www.eclipse.org/swt/faq.php#swtawtosx">FAQ</ulink>
            for details. Also, as of the writing of this article, the SWT/AWT Bridge on
            Mac OS X is not yet complete. See bug
            <ulink url="https://bugs.eclipse.org/bugs/show_bug.cgi?id=145890">
              145890
            </ulink>
            for details.
          </para>
        </note>
        <note>
          <para>
            As of the writing of this article, use of the SWT/AWT Bridge causes hangs
            with Java 6 with the GTK look and feel on the Linux/GTK platform. Refer to
            Eclipse bug
            <ulink url="https://bugs.eclipse.org/bugs/show_bug.cgi?id=91157">91157</ulink>
            and Sun bug
            <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6386791">
              6386791
            </ulink>
            for more information.
          </para>
        </note>
      </section>
      <section id="sec-event-threads">
        <title>Multiple Event Threads</title>
        <para>
          Swing/SWT integration has important threading implications. Each UI toolkit has its own
          event queue, and each event queue is processed by a separate thread. Most SWT
          APIs must be called from the SWT event thread. Swing has similar
          restrictions though they are not as strictly enforced.
          This split is the major drawback of mixing the toolkits, and it adds some
          complexity to the code.
        </para>
        <para>
          Applications must be aware of the current thread, and, where necessary,
          schedule tasks to run on the appropriate UI toolkit thread. To schedule work on
          the AWT event thread, use:
        </para>
        <itemizedlist>
          <listitem>
            <simpara>
              <code>javax.swing.SwingUtilities.invokeLater()</code>
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <code>javax.swing.SwingUtilities.invokeAndWait()</code>
            </simpara>
          </listitem>
        </itemizedlist>
        <para>To schedule work on the SWT event thread, use:</para>
        <itemizedlist>
          <listitem>
            <simpara>
              <code>org.eclipse.swt.widgets.Display.asyncExec()</code>
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <code>org.eclipse.swt.widgets.Display.syncExec()</code>
            </simpara>
          </listitem>
        </itemizedlist>
        <para>
          These are the same APIs used in a single-toolkit environment 
          to keep the UI responsive while offloading long running operations to a worker
          thread. With Swing/SWT integration they are used for the 
          additional purpose of moving work from one event thread to another.
        </para>
        <para>
          The use of multiple event threads increases the risk of deadlock. 
          Whenever possible, try to avoid blocking one event thread while 
          scheduling work on the other event thread. In other words,
          avoid calling <code>SwingUtilities.invokeAndWait</code> from the SWT event
          thread and avoid calling <code>Display.syncExec</code> from the AWT event thread. 
          Otherwise, if there's ever a case where one blocking call is made while the
          other thread has made its own blocking call in the other direction, 
          deadlock will occur. 
        </para>
      </section>
	</section>
    <section id="sec-adding-to-bridge">
      <title>Building on the SWT/AWT Bridge</title>
      <para>
        If you use the SWT/AWT Bridge API alone, Swing components will integrate poorly
        into your application. The following sections 
        describe the integration problems in detail and suggest solutions. All of the solutions 
        involve additional code to help manage the Swing/SWT integration. The 
        good news is that this code can be encapsulated in a single custom
        embedded composite widget (and some support classes), and it can be decoupled from 
        the rest of the application
        code. 
      </para>
      <section id="sec-look-and-feel">
        <title>Configuring the Swing Look and Feel</title>
        <para>
          Here's an example showing some very basic visual problems that result from 
          minimal use of the SWT/AWT Bridge on the Windows platform. 
        </para>
        <figure id="fig-badembed">
          <title>Minimal Embedding of a Swing Component</title>
          <mediaobject>
            <imageobject>
              <imagedata fileref="images/badembed.jpg"/>
            </imageobject>
          </mediaobject>
        </figure>
        <para>
          There are some immediately obvious problems here. The header and scrollbars on the Swing
          <code>JTable</code> (upper right) differ from the SWT-based Error Log view. 
        </para>
        <para>
          In this example, the <code>JTable</code> is displayed with the standard 
          Swing cross-platform (Metal) 
            <ulink
              url="http://java.sun.com/docs/books/tutorial/ui/features/plaf.html">
          look and feel 
            </ulink>.
          On the other hand, the 
          SWT components use underlying native widgets 
          which have a native look and feel. Swing's
          look and feel must be changed to match the 
          native platform. Since the SWT/AWT Bridge itself does not automatically set 
          the native look and feel, it's necessary to do it yourself. For
          example, 
        </para>
        <programlisting>
import javax.swing.UIManager;
...      
  UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
...  
        </programlisting>
        <para>
          Make this call once, before any 
          AWT or Swing components are created. 
        </para>
        <tip>
        <para>
          Linux/GTK developers: depending on the window manager in use, the Swing system 
          look and feel may not be set to the GTK look and feel. It may be necessary to 
          set the GTK look and feel more explicitly:
        <programlisting>
  UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
        </programlisting>
        </para>
        </tip>
      </section>
      <section id="sec-root-pane-container">
        <title>Creating a Root Pane Container</title>
        <para>
          The
          <code>SWT_AWT.new_Frame()</code>
          method returns an instance of a subclass of <code>java.awt.Frame</code> that has been embedded within an SWT
          <code>Composite</code>. There are certain rules that must be followed when using
          an embedded frame in Swing. 
        </para>
        <itemizedlist>
        <listitem>
        <para>
          The first child of the embedded frame must be a heavyweight component. The
          component must fill the entire frame. This heavyweight component allows for correct mouse locations and
          interactions. See Sun bug <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4982522">4982522</ulink>
          for more information. 
        </para>
        </listitem>
        <listitem>
        <para>
          To make the frame viable for use with Swing, you must also create a
          <ulink
            url="http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/JRootPane.html">
            root pane
          </ulink>container (<code>javax.swing.RootPaneContainer</code>). The root pane is the basis for all Swing windows. It provides the layering
          capabilities on which all Swing components depend. 
        </para>
        </listitem>
        <listitem>
        <para>
          Due to assumptions in the Swing implementation, the root pane container
          should be an instance of <code>JFrame</code>, <code>JDialog</code>, <code>JWindow</code>, or <code>JApplet</code>. 
          Of these options,
          only <code>JApplet</code> is an appropriate choice, since it is the only one that can
          be embedded.
        </para>
        </listitem>
        </itemizedlist>
        <para>
          To satisfy each of these rules, create a <code>JApplet</code> as the only child of the
          embedded frame. Use of <code>JApplet</code> does not imply that you have created a true
          applet with an applet's lifecycle; you are simply using the same display
          container as an applet embedded in a browser.
        </para>
      <programlisting>
    Composite composite = new Composite(parent, SWT.EMBEDDED | SWT.NO_BACKGROUND);
    Frame frame = SWT_AWT.new_Frame(composite);
    JApplet applet = new JApplet();
    frame.add(applet);
      </programlisting>
        <note>
          <para>
            The embedded frame is a window (a subclass of <code>java.awt.Window</code>). As such,
            it consumes resources. For this reason we encourage the use of embedded
            frames as replacements for larger components rather than smaller ones.
          </para>
        </note>
      </section>
      <section id="sec-reducing-flicker">
        <title>Reducing Flicker</title>
        <para>
          Use of the SWT/AWT Bridge, without additional measures, causes excessive
          flicker in an embedded AWT frame while the application window is resized. The 
          reasons include:
        </para>
        <itemizedlist>
        <listitem>
        <para>
          A heavyweight component (<code>javax.swing.JApplet</code>, in our case) is present in the component
          hierarchy. The AWT implementation, by default, clears the component's background on every resize event. 
        </para>
        </listitem>
        <listitem>
        <para>
          More resize events are handled by the embedded frame, when compared to the default
          behavior in a standalone Swing application. This increase is due to the way resize
          events are passed on to the AWT frame from the enclosing SWT composite.
        </para>
        </listitem>
        </itemizedlist>
        <para>
          On Windows, set the property
          <code>sun.awt.noerasebackground</code> to reduce flicker. This undocumented property 
          disables much of the repetitive
          background clearing by the AWT implementation. It should be set before any
          AWT or Swing components are instantiated.
        </para>
        <programlisting>
  System.setProperty("sun.awt.noerasebackground", "true");
        </programlisting>
        <note>
        <para>
          The <code>sun.awt.noerasebackground</code> property is not used on non-Windows platforms. 
          Reducing resize flicker on those platforms remains an open problem.
        </para>
        </note>
        <para>
          Though it is necessary, setting
          <code>sun.awt.noerasebackground</code>
          has negative consequences. Leaving the background uncleared may result in the
          temporary display of previously drawn pixels (an example of what is sometimes called
          <ulink url="http://inside-swt.blogspot.com/2006/08/swt-speak-part-1.html">cheese</ulink>)
          during resize operations and before the initial Swing contents
          are displayed.
        </para>
        <para>
          These effects are removed by adding a resize listener to the parent
          SWT composite. When the composite is resized larger, exposing an unpainted
          region, the listener fills it immediately with the background color. The 
          cheese is removed immediately, providing a cosmetic improvement during any delay
          while the embedded Swing component repaints. 
        </para>
        <programlisting>
class CleanResizeListener extends ControlAdapter {
  private Rectangle oldRect = null;
  public void controlResized(ControlEvent e) {
      // Prevent garbage from Swing lags during resize. Fill exposed areas 
      // with background color. 
      Composite composite = (Composite)e.widget;
      Rectangle newRect = composite.getClientArea();
      if (oldRect != null) {
          int heightDelta = newRect.height - oldRect.height;
          int widthDelta = newRect.width - oldRect.width;
          if ((heightDelta > 0) || (widthDelta > 0)) {
              GC gc = new GC(composite);
              try {
                  gc.fillRectangle(newRect.x, oldRect.height, newRect.width, heightDelta);
                  gc.fillRectangle(oldRect.width, newRect.y, widthDelta, newRect.height);
              } finally {
                  gc.dispose();
              }
          }
      }
      oldRect = newRect;
  }
}
        </programlisting>
      </section>
      <section id="sec-tab-traversal">
        <title>Tab Traversal</title>
        <para>
          Another concern of Swing/SWT integration is the behavior of the tab 
          key when traversing between components from different toolkits.
          Additional work is needed on the AWT side of the SWT/AWT
          bridge to solve this problem. To achieve proper tab traversal, implement a custom 
          subclass of <code>java.awt.FocusTraversalPolicy</code> for the embedded AWT frame. 
          The custom policy may delegate to a standard policy when
          tabbing within the frame, but it must transfer control to an SWT 
          component when:
        </para>
        <orderedlist>
        <listitem>
        <simpara>
          tabbing on the last component in the frame 
        </simpara>
        </listitem>
        <listitem>
        <simpara>
          back-tabbing on the first component in the frame
        </simpara>
        </listitem>
        </orderedlist>
        <para>
          Implementing the forward and backward traversals in the custom policy is simple. 
          However, implementing a proper <code>getDefaultComponent</code> method is tricky. It
          must return null when nothing in the embedded AWT frame has focus. This behavior is a hack based on 
          assumptions about how AWT will call the method, and it is necessary to avoid an immediate
          transfer of focus back to AWT after traversing to SWT. For more information, refer to the comments
          in the class <code>EmbeddedChildFocusTraversalPolicy</code> in <xref linkend="app-example-code"/>.
        </para>
        <para>
          See the Swing documentation for the 
          <ulink url="http://java.sun.com/j2se/1.5.0/docs/api/java/awt/doc-files/FocusSpec.html">AWT Focus Subsystem</ulink>
          for more information on focus traversal policies.
        </para>
      </section>
      <section id="sec-modality">
        <title>Modal Dialogs</title>
        <para>
          When a
          modal dialog is opened from a Swing component, it must be modal across the
          entire application. Since SWT and AWT have separate event threads,
          such dialogs are not modal by default. The SWT event thread must
          be explicitly disabled during the time that a Swing modal dialog is showing.
          This effect is most easily achieved by opening a modal SWT dialog while the 
          Swing dialog is showing. 
        </para>
        <programlisting>
  java.awt.Dialog awtDialog = ...        
  Shell shell = new Shell(parent, SWT.APPLICATION_MODAL | SWT.NO_TRIM);
  shell.setSize(0, 0);
  shell.addFocusListener(new FocusAdapter() {
      public void focusGained(FocusEvent e) {
          awtDialog.requestFocus();
          awtDialog.toFront();
      }
  });
        </programlisting>
        
        <para>
          The 0 x 0 size prevents the shell from being seen. The focus listener makes
          sure that control is restored to the Swing dialog if the SWT window somehow gains focus. 
          (For example, the SWT window may gain focus when the user navigates to your application
           through some window managers.)
        </para>
        <note>
          <para>
            On Linux/GTK, even a zero-sized SWT dialog may appear as a small dot 
            on the screen. Hide it by adding the following code to 
            <code>focusGained()</code>. This addition is unnecessary under Windows and 
            actually causes a flash, so make the call only when required.
          </para>
          <programlisting>
          shell.moveBelow(null);
          </programlisting>
        </note>
        <para>
          The code shown above ensures correct modal behavior, but how should it be invoked?
          The easiest approach is to invoke it wherever Swing modal dialogs are created. 
          However, this solution won't work if your Swing component library cannot be 
          modified, or if you cannot introduce dependencies on SWT code from
          the Swing component library. 
        </para>
        <para>
          Alternatively, correct modal behavior is enforced more cleanly by installing a listener for all AWT
          window events. Whenever it is detected that a Swing modal dialog is open or visible, a
          SWT modal dialog must be opened. The listener is sketched below and is
          fully implemented in the example code. See <xref linkend="app-example-code"/> for more
          information. 
        </para>
        <programlisting>
class AwtDialogListener implements AWTEventListener, ComponentListener {
    
    private final Display display;
    
    AwtDialogListener(Display display) {
        this.display = display;
        Toolkit.getDefaultToolkit().addAWTEventListener(this, AWTEvent.WINDOW_EVENT_MASK);
    }
    
    private void handleRemovedDialog(Dialog awtDialog, boolean removeListener) {
        // An AWT dialog has been closed or set invisible. Close the SWT dialog
        ...
    }

    private void handleAddedDialog(final Dialog awtDialog) {
        // An AWT dialog has been opened or set visible. Open the SWT dialog
        // and add this as a component listener on the dialog to catch
        // visibility changes
        ...
    }

    private void handleOpenedWindow(WindowEvent event) {
        Window window = event.getWindow();
        if (window instanceof Dialog) {
            handleAddedDialog((Dialog)window);
        }
    }
    
    private void handleClosedWindow(WindowEvent event) {
        // Dispose-based close
        Window window = event.getWindow();
        if (window instanceof Dialog) {
            // Remove dialog and component listener
            handleRemovedDialog((Dialog)window, true);
        }
    }

    private void handleClosingWindow(WindowEvent event) {
        // System-based close 
        // (see example code for full implementation)
        ...
    }
    
    public void eventDispatched(AWTEvent event) {
        switch (event.getID()) {
        case WindowEvent.WINDOW_OPENED:
            handleOpenedWindow((WindowEvent)event);
            break;
            
        case WindowEvent.WINDOW_CLOSED:
            handleClosedWindow((WindowEvent)event);
            break;

        case WindowEvent.WINDOW_CLOSING:
            handleClosingWindow((WindowEvent)event);
            break;

        default:
            break;
        }
    }

    public void componentHidden(ComponentEvent e) {
        Object obj = e.getSource();
        if (obj instanceof Dialog) {
            // Remove dialog but keep listener in place so that we know if/when it is set visible
            handleRemovedDialog((Dialog)obj, false);
        }
    }

    public void componentShown(ComponentEvent e) {
        Object obj = e.getSource();
        if (obj instanceof Dialog) {
            handleAddedDialog((Dialog)obj);
        }
    }
  ...
}
        </programlisting>
      </section>
      <section id="sec-dismissing-popups">
        <title>Dismissing Pop-up Menus</title>
        <para>
          When a context menu is displayed in an embedded AWT frame, the menu does not
          disappear after clicking outside the frame. This AWT limitation is well known,
          but it is especially noticeable in embedded frames since it may result in
          multiple visible pop-ups within the same SWT shell. 
        </para>
        <figure id="fig-double-popup">
          <title>Double Popups</title>
          <mediaobject>
            <imageobject>
              <imagedata fileref="images/double-popup.jpg"/>
            </imageobject>
          </mediaobject>
        </figure>
        <para>
          This issue is documented in Sun bugs 
          <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4311449">4311449</ulink>
          and <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4290715">4290715</ulink>,
          among others.
        </para>
        <para>There are partial workarounds to this problem:</para>
        <itemizedlist>
        <listitem>
        <para>
          <emphasis>Manually dismiss Swing pop-ups when the user activates other windows.</emphasis> Install a
          listener for window focus events on the embedded frame. On a focus lost event, the window
          and component hierarchies of the frame can be searched for instances of
          <code>javax.swing.JPopupMenu</code>.
          <note>
            <para>
              This workaround applies to JRE version 1.4 and earlier; it should not be
              necessary if you are using version 1.5 or later.
            </para>
          </note>
        </para>
        </listitem>
        <listitem>
        <para>
          <emphasis>Manually dismiss Swing pop-ups when the user activates an SWT menu.</emphasis> Install 
          a display filter to listen for <code>SWT.Show</code> events which are generated whenever an
          SWT menu is shown. In the filter's event handler, visible Swing pop-ups can be dismissed as described 
          above. 
        </para>
        </listitem>
        </itemizedlist>
        <para>
          Despite these workarounds, some issues remain; for example, Swing pop-ups are not
          dismissed when the user interacts with the titlebar on the workbench window. 
        </para>
      </section>
      <section id="sec-system-settings">
        <title>Synchronizing with System Settings</title>
        <para>
          When the user changes font settings through the Windows control panel, the
          changes are not always properly propagated to Swing components. This problem is
          especially noticeable when integrating with SWT since the SWT components do, in fact,
          recognize these changes. To work around the problem, manually
          change the font in the Swing Windows Look and Feel when the system font has changed.
        </para>
        <para>
          Fortunately, in Eclipse 3.2, a new SWT event has been added to allow applications
          to detect changes to system settings. So, Swing font changes can be triggered
          as follows
        </para>
        <programlisting>
    Display display = ...
    Listener settingsListener = new Listener() {
        public void handleEvent(Event event) {
            handleSettingsChange();
        }
    };
    display.addListener(SWT.Settings, settingsListener);
        </programlisting>
        <para>
          Font changes for Swing components are best handled through the 
          look and feel, rather than updating the font for individual components. 
        </para>        
        <programlisting>
    private void handleSettingsChange() {
            ...
            org.eclipse.swt.graphics.Font currentSystemFont = ...;
            FontData fontData = currentSystemFont.getFontData()[0];
            
            int resolution = Toolkit.getDefaultToolkit().getScreenResolution();
            int awtFontSize = (int)Math.round((double)fontData.getHeight() * resolution / 72.0);
            
            // The style constants for SWT and AWT map exactly, and since they are int constants, they should
            // never change. So, the SWT style is passed through as the AWT style. 
            java.awt.Font awtFont = new java.awt.Font(fontData.getName(), fontData.getStyle(), awtFontSize);

            FontUIResource fontResource = new FontUIResource(awtFont);
    
            UIManager.put("Button.font", fontResource); 
            UIManager.put("CheckBox.font", fontResource); 
            UIManager.put("ComboBox.font", fontResource); 
            ...    // many more similar calls

            Container contentPane = ... // content pane from the root pane 
            SwingUtilities.updateComponentTreeUI(contentPane);
        }
    }
        </programlisting>        
        <para>
          First, the SWT font is converted to an equivalent AWT font. 
          AWT font sizes always assume a 72 dpi resolution. The true screen resolution must be 
          used to convert the platform font size into an AWT point size that matches when displayed. 
          Then, the font for various Swing component types is changed via the look and feel's
          <code>javax.swing.UIManager</code>. 
        </para>
        <para>
          See the example code (<xref linkend="app-example-code"/>) for the complete implementation.
        </para>
      </section>
      <section id="sec-keystroke-contention">
        <title>Keystroke Contention</title>
        <para>
          Unexpected results can occur if you map the same keystroke to a global action
          in your RCP application and to a handler in an embedded Swing component. 
          Keystrokes defined through the <code><ulink url="http://help.eclipse.org/help32/index.jsp?topic=/org.eclipse.platform.doc.isv/reference/extension-points/org_eclipse_ui_bindings.html">
          org.eclipse.ui.bindings</ulink></code> extension point will take precedence over those
          defined in the Swing component, even if the Swing component has focus. In this case, the
          RCP binding is managed through a Display filter, so the keystroke is consumed before
          it reaches the Swing component at all. As a result, there is no simple, general 
          workaround to avoid this problem at the level of the embedded composite. Instead, you
          can avoid these conflicts by:
          <itemizedlist>
          <listitem>
          <para>
            Using the <code><ulink url="http://help.eclipse.org/help32/index.jsp?topic=/org.eclipse.platform.doc.isv/reference/extension-points/org_eclipse_ui_contexts.html">
            org.eclipse.ui.contexts</ulink></code> extension point to organize key bindings that should 
            not be visible when the Swing component is in focus.
          </para>
          </listitem>
          <listitem>
          <para>
            Replicate the Swing component's action in an RCP action, bound to the same keystroke. The 
            binding for RCP action can be introduced through an <code>org.eclipse.ui.contexts</code>
            extension. The action can be implemented to invoke the underlying the Swing action. This
            approach may be necessary anyway, if you want the action to be available anywhere outside
            the Swing component (for example, in the application's main menu).
          </para>
          </listitem>
          </itemizedlist>
        </para>
        <para>
          There are also occasional issues with keystroke contention between the embedded Swing 
          component and the window system. For example, hitting Shift-F10 from inside many Swing 
          components opens a context (popup) menu. In Windows, when there is no context menu, the default 
          processing of the F10 keystroke
          (with or without shifting) transfers focus to the application's main menu bar.
          When you have embedded Swing components, these two behaviors conflict. 
          The Swing component properly handles Shift-F10, showing the popup, but the containing SWT shell does 
          not know it; therefore, it reports the keystroke to Windows as unhandled. Windows then 
          transfers focus to the main menu bar, and the popup loses focus.
        </para>
        <para>
          Fortunately, this conflict can be resolved.  Here's some code which exploits the fact that 
          the default Windows behavior happens when F10 is released, rather than when it is pressed. 
          The embedded composite can install a KeyListener and consume the release of the 
          Shift-F10 keystroke so that Windows never sees it. 
        </para>
        <programlisting>
    public void keyReleased(KeyEvent e) {
        if (e.keyCode == SWT.F10 &amp;&amp; (e.stateMask &amp; SWT.SHIFT) != 0) {
            e.doit = false;
        }
    }
        </programlisting>
      </section>
      <section id="sec-other-workarounds">
        <title>Other Workarounds</title>
        <para>
          Due to Sun bug <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6411042">6411042</ulink>,
          when AWT/Swing components are
          added to an embedded frame from the SWT event thread, a memory leak occurs. To 
          avoid the leak, it is best to create and add these components from the AWT event thread 
          instead. Simply invoke the creation code through
          <code>javax.swing.SwingUtilities.invokeLater()</code>.
          As discussed earlier, it is a good general habit to call Swing APIs from the 
          AWT event thread anyway. 
        </para>
      </section>
    </section>
      <section id="sec-unresolved-issues">
        <title>Unresolved Issues</title>
        <section id="sec-cleartype">
        <title>ClearType</title>
        <para>
          On Windows under JRE 1.5 and earlier, the Swing system look and feel does not 
          seamlessly support <ulink url="http://www.microsoft.com/typography/ClearTypeInfo.mspx">ClearType</ulink>
          anti-aliasing. By default, when ClearType is enabled and the same font and font
          size are chosen for Swing and SWT controls, the fonts appear to be different. A
          partial solution is available through setting the 
          property <code>swing.aatext</code> to "true". This undocumented property enables font anti-aliasing
          in pre-Java 6 environments, but it simply turns anti-aliasing on. It does not synchronize with current 
          Windows system settings. Also, Swing has its own anti-aliasing algorithm, so  
          minor differences from natively-displayed fonts remain visible. 
        </para>
        <para>
          This problem has been <ulink url="http://weblogs.java.net/blog/chet/archive/2005/06/phils_font_fixe.html">resolved</ulink>
          in Java 6 (see bugs <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4726365">4726365</ulink>
          and <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4871297">4871297</ulink> 
          for more information).
        </para>
        <para>
        Below is a screenshot which illustrates the problem. Here, two SWT-based views are on
        the left, and a Swing table component is on the right.
        </para>
        <figure id="fig-cleartype">
          <title>Font Differences with ClearType</title>
          <mediaobject>
            <imageobject>
              <imagedata fileref="images/cleartype.jpg"/>
            </imageobject>
          </mediaobject>
        </figure>
        </section>
        <section id="sec-cursor-synchronization">
        <title>Cursor Synchronization</title>
        <para>
          SWT cursor changes are not reflected in embedded Swing components. The SWT cursor
          changes back to the default arrow cursor as the mouse moves over the embedded frame.
        </para>
        <para>
          A solution to this problem may now be possible. As of Eclipse 3.3, new API is 
          available to query the current cursor (see bug
          <ulink url="https://bugs.eclipse.org/bugs/show_bug.cgi?id=133943">133943</ulink>
          ).
        </para>
        </section>
      </section>
      <section id="sec-conclusion">
      <title>Conclusion</title>
      <para>
        Smooth integration of Swing components into an RCP application is possible. It requires 
        more than the SWT/AWT Bridge, however. You can implement the techniques described above
        in a modular fashion to improve the behavior of the SWT/AWT Bridge for 
        real-world applications. <xref linkend="app-example-code"/> contains example
        code that demonstrates all of these additional practices. 
      </para>
      </section>

      <bibliography id="bin-resources">
        <title>Resources</title>

        <biblioentry id="bib-example-code">
          <bibliosource><ulink url="files/swingintegration.example_0.0.2.jar">Example Code</ulink></bibliosource> 
        </biblioentry>

        <biblioentry id="bib-bridge">
          <bibliosource>
            <ulink
              url="http://help.eclipse.org/help32/topic/org.eclipse.platform.doc.isv/reference/api/org/eclipse/swt/awt/package-summary.html">
              SWT/AWT Bridge Javadoc
            </ulink>
          </bibliosource>
        </biblioentry>
        <biblioentry id="bib-look-and-feel">
          <bibliosource>
            <ulink
              url="http://java.sun.com/docs/books/tutorial/ui/features/plaf.html">
              Java Look and Feel Information
            </ulink>

          </bibliosource>
        </biblioentry>
        <biblioentry id="bib-root-pane">
          <bibliosource>
            <ulink
              url="http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/JRootPane.html">
              Swing Root Pane Documentation
            </ulink>

          </bibliosource>
        </biblioentry>
        <biblioentry id="bib-awt-focus">
          <bibliosource>
            <ulink url="http://java.sun.com/j2se/1.5.0/docs/api/java/awt/doc-files/FocusSpec.html">AWT Focus Subsystem</ulink>
          </bibliosource>
        </biblioentry>
      </bibliography>

      <appendix id="app-example-code">
		<title>Example Code</title>
         <para>
           The ideas for improving Swing/SWT integration presented in 
           <xref linkend="sec-adding-to-bridge"/> have been collected into a full
           example implementation <xref linkend="bib-example-code"/>. The example
           includes an API that is used to create embedded Swing components
           simply and cleanly. The example code requires SWT version 3.2 or higher.
         </para>
         <para>
          Import the example with "File -> Import...", selecting "Plug-ins and Fragments". Import the 
          plug-in as "Projects with Source Folders". Make sure that your
          compiler settings specify a source compatibility version of at least 1.4 (Preferences -> Java -> Compiler). 
          Otherwise the <code>assert</code> statements in the example code will not compile.
         </para>
         <para>
           <ulink url="files/example-javadoc/index.html">Javadoc</ulink>
           is available for the API. To embed Swing components, refer to
           the javadoc for
           <code>
             <ulink
               url="files/example-javadoc/swingintegration/example/EmbeddedSwingComposite.html">
               EmbeddedSwingComposite</ulink></code>. To display Swing dialogs without embedding, refer to the javadoc for
           <code>
             <ulink url="files/example-javadoc/swingintegration/example/AwtEnvironment.html">
               AwtEnvironment</ulink></code>.
         </para>
      </appendix>
</article>