libjava/java/awt/Container.java

/* Copyright (C) 1999, 2000, 2002  Free Software Foundation

This file is part of GNU Classpath.

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package java.awt;

import java.awt.event.*;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.util.EventListener;
import java.awt.peer.ComponentPeer;
import java.awt.peer.ContainerPeer;
import java.awt.peer.LightweightPeer;

/* A somewhat incomplete class. */

public class Container extends Component
{
  /* Serialized fields from the serialization spec. */
  int ncomponents;
  Component[] component;
  LayoutManager layoutMgr;
  /* LightweightDispatcher dispatcher; */ // wtf?
  Dimension maxSize;
  int containerSerializedDataVersion;

  /* Anything else is non-serializable, and should be declared "transient". */
  transient ContainerListener containerListener;  

  /**
   * Default constructor for subclasses.
   */
  public Container()
  {
  }

  /**
   * Returns the number of components in this container.
   *
   * @return The number of components in this container.
   */
  public int getComponentCount()
  {
    return ncomponents;
  }

  /**
   * Returns the number of components in this container.
   *
   * @return The number of components in this container.
   *
   * @deprecated This method is deprecated in favor of 
   * <code>getComponentCount()</code>.
   */
  public int countComponents()
  {
    return ncomponents;
  }

  /**
   * Returns the component at the specified index.
   *
   * @param index The index of the component to retrieve.
   *
   * @return The requested component.
   *
   * @exception ArrayIndexOutOfBoundsException If the specified index is not
   * valid.
   */
  public Component getComponent (int n)
  {
    if (n < 0 || n >= ncomponents)
      throw new ArrayIndexOutOfBoundsException("no such component");
    return component[n];
  }

  /**
   * Returns an array of the components in this container.
   *
   * @return The components in this container.
   */
  public Component[] getComponents()
  {
    Component[] result = new Component[ncomponents];
    if (ncomponents > 0)
      System.arraycopy(component, 0, result, 0, ncomponents);
    return result;
  }

  /**
   * Returns the insets for this container, which is the space used for
   * borders, the margin, etc.
   *
   * @return The insets for this container.
   */
  public Insets getInsets()
  {
    if (peer == null)
      return new Insets(0, 0, 0, 0);
    return ((ContainerPeer) peer).getInsets();
  }

  /**
   * Returns the insets for this container, which is the space used for
   * borders, the margin, etc.
   *
   * @return The insets for this container.
   *
   * @deprecated This method is deprecated in favor of
   * <code>getInsets()</code>.
   */
  public Insets insets()
  {
    return getInsets();
  }

  /**
   * Adds the specified component to this container at the end of the
   * component list.
   *
   * @param component The component to add to the container.
   *
   * @return The same component that was added.
   */
  public Component add (Component comp)
  {
    addImpl (comp, null, -1);
    return comp;
  }

  /**
   * Adds the specified component to the container at the end of the
   * component list.  This method should not be used. Instead, use
   * <code>add(Component, Object</code>.
   *
   * @param name FIXME
   * @param component The component to be added.
   *
   * @return The same component that was added.
   */
  public Component add (String name, Component comp)
  {
    addImpl (comp, name, -1);
    return comp;
  }

  /**
   * Adds the specified component to this container at the specified index
   * in the component list.
   *
   * @param component The component to be added.
   * @param index The index in the component list to insert this child
   * at, or -1 to add at the end of the list.
   *
   * @return The same component that was added.
   *
   * @param throws ArrayIndexOutOfBounds If the specified index is invalid.
   */
  public Component add (Component comp, int index)
  {
    addImpl (comp, null, index);
    return comp;
  }

  /**
   * Adds the specified component to this container at the end of the
   * component list.  The layout manager will use the specified constraints
   * when laying out this component.
   *
   * @param component The component to be added to this container.
   * @param constraints The layout constraints for this component.
   */
  public void add (Component comp, Object constraints)
  {
    addImpl (comp, constraints, -1);
  }

  /**
   * Adds the specified component to this container at the specified index
   * in the component list.  The layout manager will use the specified
   * constraints when layout out this component.
   *
   * @param component The component to be added.
   * @param constraints The layout constraints for this component.
   * @param index The index in the component list to insert this child
   * at, or -1 to add at the end of the list.
   *
   * @param throws ArrayIndexOutOfBounds If the specified index is invalid.
   */
  public void add (Component comp, Object constraints, int index)
  {
    addImpl (comp, constraints, index);
  }

  /**
   * This method is called by all the <code>add()</code> methods to perform
   * the actual adding of the component.  Subclasses who wish to perform
   * their own processing when a component is added should override this
   * method.  Any subclass doing this must call the superclass version of
   * this method in order to ensure proper functioning of the container.
   *
   * @param component The component to be added.
   * @param constraints The layout constraints for this component, or
   * <code>null</code> if there are no constraints.
   * @param index The index in the component list to insert this child
   * at, or -1 to add at the end of the list.
   *
   * @param throws ArrayIndexOutOfBounds If the specified index is invalid.
   */
  protected void addImpl (Component comp, Object constraints, int index)
  {
    if (index > ncomponents
	|| (index < 0 && index != -1)
	|| comp instanceof Window
	|| (comp instanceof Container
	    && ((Container) comp).isAncestorOf (this)))
      throw new IllegalArgumentException ();

    // Reparent component, and make sure component is instantiated if
    // we are.
    if (comp.parent != null)
      comp.parent.remove (comp);
    comp.parent = this;
    if (peer != null)
      {
	comp.addNotify ();

	if (comp.isLightweight())
	  enableEvents(comp.eventMask);
      }

    invalidate ();

    if (component == null)
      component = new Component[4]; // FIXME, better initial size?

    // This isn't the most efficient implementation.  We could do less
    // copying when growing the array.  It probably doesn't matter.
    if (ncomponents >= component.length)
      {
	int nl = component.length * 2;
	Component[] c = new Component[nl];
	System.arraycopy (component, 0, c, 0, ncomponents);
	component = c;
      }
    if (index == -1)
      component[ncomponents++] = comp;
    else
      {
	System.arraycopy (component, index, component, index + 1,
			  ncomponents - index);
	component[index] = comp;
	++ncomponents;
      }

    // Notify the layout manager.
    if (layoutMgr != null)
      {
	if (layoutMgr instanceof LayoutManager2)
	  {
	    LayoutManager2 lm2 = (LayoutManager2) layoutMgr;
	    lm2.addLayoutComponent (comp, constraints);
	  }
	else if (constraints instanceof String)
	  layoutMgr.addLayoutComponent ((String) constraints, comp);
	else
	  layoutMgr.addLayoutComponent (null, comp);
      }

    // Post event to notify of adding the container.
    ContainerEvent ce = new ContainerEvent (this,
					    ContainerEvent.COMPONENT_ADDED,
					    comp);
    getToolkit().getSystemEventQueue().postEvent(ce);
  }

  /**
   * Removes the component at the specified index from this container.
   *
   * @param index The index of the component to remove.
   */
  public void remove (int index)
  {
    Component r = component[index];

    r.removeNotify ();

    System.arraycopy (component, index + 1, component, index,
		      ncomponents - index - 1);
    component[--ncomponents] = null;

    invalidate ();

    if (layoutMgr != null)
      layoutMgr.removeLayoutComponent (r);

    // Post event to notify of adding the container.
    ContainerEvent ce = new ContainerEvent (this,
					    ContainerEvent.COMPONENT_REMOVED,
					    r);
    getToolkit().getSystemEventQueue().postEvent(ce);
  }

  /**
   * Removes the specified component from this container.
   *
   * @return component The component to remove from this container.
   */
  public void remove (Component comp)
  {
    for (int i = 0; i < ncomponents; ++i)
      {
	if (component[i] == comp)
	  {
	    remove (i);
	    break;
	  }
      }
  }

  /**
   * Removes all components from this container.
   */
  public void removeAll()
  {
    while (ncomponents > 0)
      remove (0);
  }

  /**
   * Returns the current layout manager for this container.
   *
   * @return The layout manager for this container.
   */
  public LayoutManager getLayout()
  {
    return layoutMgr;
  }

  /**
   * Sets the layout manager for this container to the specified layout
   * manager.
   *
   * @param mgr The new layout manager for this container.
   */
  public void setLayout(LayoutManager mgr)
  {
    layoutMgr = mgr;
    invalidate ();
  }

  /**
   * Layout the components in this container.
   */
  public void doLayout()
  {
    if (layoutMgr != null)
      layoutMgr.layoutContainer (this);
  }

  /**
   * Layout the components in this container.
   *
   * @deprecated This method is deprecated in favor of
   * <code>doLayout()</code>.
   */
  public void layout()
  {
    doLayout();
  }

  /**
   * Invalidates this container to indicate that it (and all parent
   * containers) need to be laid out.
   */
  public void invalidate()
  {
    super.invalidate ();
  }

  /**
   * Re-lays out the components in this container.
   */
  public void validate()
  {
    // FIXME: use the tree lock?
    synchronized (this)
      {
	if (! isValid ())
	  {
	    validateTree ();
	  }
      }
  }

  /**
   * Recursively validates the container tree, recomputing any invalid
   * layouts.
   */
  protected void validateTree()
  {
    if (valid)
      return; 

    ContainerPeer cPeer = null;
    if ((peer != null) && !(peer instanceof LightweightPeer))
      {
	cPeer = (ContainerPeer) peer;
	cPeer.beginValidate();
      }

    doLayout ();
    for (int i = 0; i < ncomponents; ++i)
      {
	Component comp = component[i];
	if (! comp.isValid ())
	  {
	    if (comp instanceof Container)
	      {
		((Container) comp).validateTree();
	      }
	    else
	      {
		component[i].validate();
	      }
	  }
      }

    /* children will call invalidate() when they are layed out. It
       is therefore imporant that valid is not set to true
       before after the children has been layed out. */
    valid = true;

    if (cPeer != null)
      cPeer.endValidate();
  }

  public void setFont(Font f)
  {
    super.setFont(f);
    // FIXME, should invalidate all children with font == null
  }

  /**
   * Returns the preferred size of this container.
   *
   * @return The preferred size of this container.
   */
  public Dimension getPreferredSize()
  {
    if (layoutMgr != null)
      return layoutMgr.preferredLayoutSize (this);
    else
      return super.getPreferredSize ();
  }

  /**
   * Returns the preferred size of this container.
   *
   * @return The preferred size of this container.
   * 
   * @deprecated This method is deprecated in favor of 
   * <code>getPreferredSize()</code>.
   */
  public Dimension preferredSize()
  {
    return getPreferredSize();
  }

  /**
   * Returns the minimum size of this container.
   *
   * @return The minimum size of this container.
   */
  public Dimension getMinimumSize()
  {
    if (layoutMgr != null)
      return layoutMgr.minimumLayoutSize (this);
    else
      return super.getMinimumSize ();
  }

  /**
   * Returns the minimum size of this container.
   *
   * @return The minimum size of this container.
   * 
   * @deprecated This method is deprecated in favor of 
   * <code>getMinimumSize()</code>.
   */
  public Dimension minimumSize()
  {
    return getMinimumSize();
  }

  /**
   * Returns the maximum size of this container.
   *
   * @return The maximum size of this container.
   */
  public Dimension getMaximumSize()
  {
    if (layoutMgr != null && layoutMgr instanceof LayoutManager2)
      {
	LayoutManager2 lm2 = (LayoutManager2) layoutMgr;
	return lm2.maximumLayoutSize (this);
      }
    else
      return super.getMaximumSize ();
  }

  /**
   * Returns the preferred alignment along the X axis.  This is a value
   * between 0 and 1 where 0 represents alignment flush left and
   * 1 means alignment flush right, and 0.5 means centered.
   *
   * @return The preferred alignment along the X axis.
   */
  public float getAlignmentX()
  {
    if (layoutMgr instanceof LayoutManager2)
      {
	LayoutManager2 lm2 = (LayoutManager2) layoutMgr;
	return lm2.getLayoutAlignmentX (this);
      }
    else
      return super.getAlignmentX();
  }

  /**
   * Returns the preferred alignment along the Y axis.  This is a value
   * between 0 and 1 where 0 represents alignment flush top and
   * 1 means alignment flush bottom, and 0.5 means centered.
   *
   * @return The preferred alignment along the Y axis.
   */
  public float getAlignmentY()
  {
    if (layoutMgr instanceof LayoutManager2)
      {
	LayoutManager2 lm2 = (LayoutManager2) layoutMgr;
	return lm2.getLayoutAlignmentY (this);
      }
    else
      return super.getAlignmentY();
  }

  /**
   * Paints this container.  The implementation of this method in this
   * class forwards to any lightweight components in this container.  If
   * this method is subclassed, this method should still be invoked as
   * a superclass method so that lightweight components are properly
   * drawn.
   *
   * @param graphics The graphics context for this paint job.
   */
  public void paint(Graphics g)
  {
    if (!isShowing())
      return;
    super.paint(g);
    visitChildren(g, GfxPaintVisitor.INSTANCE, true);
  }

  /** 
   * Perform a graphics operation on the children of this container.
   * For each applicable child, the visitChild() method will be called
   * to perform the graphics operation.
   *
   * @param gfx The graphics object that will be used to derive new
   * graphics objects for the children.
   *
   * @param visitor Object encapsulating the graphics operation that
   * should be performed.
   *
   * @param lightweightOnly If true, only lightweight components will
   * be visited.
   */
  private void visitChildren(Graphics gfx, GfxVisitor visitor,
			     boolean lightweightOnly)
  {
    // FIXME: do locking

    for (int i = 0; i < ncomponents; ++i)
      {
	Component comp = component[i];
	boolean applicable = comp.isVisible()
	  && (comp.isLightweight() || !lightweightOnly);

	if (applicable)
	  visitChild(gfx, visitor, comp);
      }
  }

  /**
   * Perform a graphics operation on a child. A translated and clipped
   * graphics object will be created, and the visit() method of the
   * visitor will be called to perform the operation.
   *
   * @param gfx The graphics object that will be used to derive new
   * graphics objects for the child.
   *
   * @param visitor Object encapsulating the graphics operation that
   * should be performed.
   *
   * @param comp The child component that should be visited.
   */
  private void visitChild(Graphics gfx, GfxVisitor visitor,
			  Component comp)
  {
    Rectangle bounds = comp.getBounds();
    Rectangle clip = gfx.getClipBounds().intersection(bounds);
    
    if (clip.isEmpty()) return;

    Graphics gfx2 = gfx.create();
    gfx2.setClip(clip.x, clip.y, clip.width, clip.height);
    gfx2.translate(bounds.x, bounds.y);
    
    visitor.visit(comp, gfx2);
  }

  /**
   * Updates this container.  The implementation of this method in this
   * class forwards to any lightweight components in this container.  If
   * this method is subclassed, this method should still be invoked as
   * a superclass method so that lightweight components are properly
   * drawn.
   *
   * @param graphics The graphics context for this update.
   */
  public void update(Graphics g)
  {
    super.update(g);
  }

  /**
   * Prints this container.  The implementation of this method in this
   * class forwards to any lightweight components in this container.  If
   * this method is subclassed, this method should still be invoked as
   * a superclass method so that lightweight components are properly
   * drawn.
   *
   * @param graphics The graphics context for this print job.
   */
  public void print(Graphics g)
  {
    super.print(g);
    visitChildren(g, GfxPrintVisitor.INSTANCE, true);
  }

  /**
   * Paints all of the components in this container.
   *
   * @param graphics The graphics context for this paint job.
   */
  public void paintComponents(Graphics g)
  {
    super.paint(g);
    visitChildren(g, GfxPaintAllVisitor.INSTANCE, true);
  }

  /**
   * Prints all of the components in this container.
   *
   * @param graphics The graphics context for this print job.
   */
  public void printComponents(Graphics g)
  {
    super.paint(g);
    visitChildren(g, GfxPrintAllVisitor.INSTANCE, true);
  }

  void dispatchEventImpl(AWTEvent e)
  {
    if ((e.id <= ContainerEvent.CONTAINER_LAST
             && e.id >= ContainerEvent.CONTAINER_FIRST)
	&& (containerListener != null
	    || (eventMask & AWTEvent.CONTAINER_EVENT_MASK) != 0))
      processEvent(e); 
    else
      super.dispatchEventImpl(e);
  }  

  /**
   * Adds the specified container listener to this object's list of
   * container listeners.
   *
   * @param listener The listener to add.
   */
  public synchronized void addContainerListener(ContainerListener l)
  {
    containerListener = AWTEventMulticaster.add (containerListener, l);
  }

  /**
   * Removes the specified container listener from this object's list of
   * container listeners.
   *
   * @param listener The listener to remove.
   */
  public synchronized void removeContainerListener(ContainerListener l)
  {
    containerListener = AWTEventMulticaster.remove(containerListener, l);
  }

  /** @since 1.3 */
  public EventListener[] getListeners(Class listenerType)
  {
    if (listenerType == ContainerListener.class)
      return getListenersImpl(listenerType, containerListener);
    else return super.getListeners(listenerType);
  }

  /**
   * Processes the specified event.  This method calls
   * <code>processContainerEvent()</code> if this method is a
   * <code>ContainerEvent</code>, otherwise it calls the superclass
   * method.
   *
   * @param event The event to be processed.
   */
  protected void processEvent(AWTEvent e)
  {
    if (e instanceof ContainerEvent)
      processContainerEvent((ContainerEvent) e);
    else super.processEvent(e);
  }

  /**
   * Called when a container event occurs if container events are enabled.
   * This method calls any registered listeners.
   *
   * @param event The event that occurred.
   */
  protected void processContainerEvent(ContainerEvent e)
  {
    if (containerListener == null)
      return;
    switch (e.id)
      {
      case ContainerEvent.COMPONENT_ADDED:
	containerListener.componentAdded(e);
	break;

      case ContainerEvent.COMPONENT_REMOVED:
	containerListener.componentRemoved(e);
	break;    
      }
  }

  /**
   * AWT 1.0 event processor.
   *
   * @param event The event that occurred.
   *
   * @deprecated This method is deprecated in favor of 
   * <code>dispatchEvent()</code>.
   */
  public void deliverEvent(Event e)
  {
  }

  /**
   * Returns the component located at the specified point.  This is done
   * by checking whether or not a child component claims to contain this
   * point.  The first child component that does is returned.  If no
   * child component claims the point, the container itself is returned,
   * unless the point does not exist within this container, in which
   * case <code>null</code> is returned.
   *
   * @param x The X coordinate of the point.
   * @param y The Y coordinate of the point.
   *
   * @return The component containing the specified point, or
   * <code>null</code> if there is no such point.
   */
  public Component getComponentAt (int x, int y)
  {
    if (! contains (x, y))
      return null;
    for (int i = 0; i < ncomponents; ++i)
      {
	// Ignore invisible children...
	if (!component[i].isVisible())
	  continue;

	int x2 = x - component[i].x;
	int y2 = y - component[i].y;
	if (component[i].contains (x2, y2))
	  return component[i];
      }
    return this;
  }

  /**
   * Returns the component located at the specified point.  This is done
   * by checking whether or not a child component claims to contain this
   * point.  The first child component that does is returned.  If no
   * child component claims the point, the container itself is returned,
   * unless the point does not exist within this container, in which
   * case <code>null</code> is returned.
   *
   * @param point The point to return the component at.
   *
   * @return The component containing the specified point, or <code>null</code>
   * if there is no such point.
   *
   * @deprecated This method is deprecated in favor of
   * <code>getComponentAt(int, int)</code>.
   */
  public Component locate(int x, int y)
  {
    return getComponentAt(x, y);
  }

  /**
   * Returns the component located at the specified point.  This is done
   * by checking whether or not a child component claims to contain this
   * point.  The first child component that does is returned.  If no
   * child component claims the point, the container itself is returned,
   * unless the point does not exist within this container, in which
   * case <code>null</code> is returned.
   *
   * @param point The point to return the component at.
   *
   * @return The component containing the specified point, or <code>null</code>
   * if there is no such point.
   */
  public Component getComponentAt(Point p)
  {
    return getComponentAt(p.x, p.y);
  }

  public Component findComponentAt (int x, int y)
  {
    if (! contains (x, y))
      return null;

    for (int i = 0; i < ncomponents; ++i)
      {
	// Ignore invisible children...
	if (!component[i].isVisible())
	  continue;

	int x2 = x - component[i].x;
	int y2 = y - component[i].y;
	// We don't do the contains() check right away because
	// findComponentAt would redundantly do it first thing.
	if (component[i] instanceof Container)
	  {
	    Container k = (Container) component[i];
	    Component r = k.findComponentAt (x2, y2);
	    if (r != null)
	      return r;
	  }
	else if (component[i].contains (x2, y2))
	  return component[i];
      }

    return this;
  }

  public Component findComponentAt(Point p)
  {
    return findComponentAt(p.x, p.y);
  }

  /**
   * Called when this container is added to another container to inform it
   * to create its peer.  Peers for any child components will also be
   * created.
   */
  public void addNotify ()
  {
    addNotifyContainerChildren ();
    super.addNotify();
  }

  private void addNotifyContainerChildren()
  {
    for (int i = ncomponents;  --i >= 0; )
      {
	component[i].addNotify();
	if (component[i].isLightweight())
	  enableEvents(component[i].eventMask);
      }
  }

  /**
   * Called when this container is removed from its parent container to
   * inform it to destroy its peer.  This causes the peers of all child
   * component to be destroyed as well.
   */
  public void removeNotify()
  {
    for (int i = 0; i < ncomponents; ++i)
      component[i].removeNotify ();
    super.removeNotify();
  }

  /**
   * Tests whether or not the specified component is contained within
   * this components subtree.
   *
   * @param component The component to test.
   *
   * @return <code>true</code> if this container is an ancestor of the
   * specified component, <code>false</code>.
   */
  public boolean isAncestorOf (Component comp)
  {
    for (;;)
      {
	if (comp == null)
	  return false;
	if (comp == this)
	  return true;
	comp = comp.getParent();
      }
  }

  /**
   * Returns a string representing the state of this container for
   * debugging purposes.
   *
   * @return A string representing the state of this container.
   */
  protected String paramString()
  {
    String param = super.paramString();
    if (layoutMgr != null)
      param = param + "," + layoutMgr.getClass().getName();

    return param;
  }

  /**
   * Writes a listing of this container to the specified stream starting
   * at the specified indentation point.
   *
   * @param stream The <code>PrintStream</code> to write to.
   * @param indent The indentation point.
   */
  public void list (PrintStream out, int indent)
  {
    super.list (out, indent);
    for (int i = 0; i < ncomponents; ++i)
      component[i].list (out, indent + 2);
  }

  /**
   * Writes a listing of this container to the specified stream starting
   * at the specified indentation point.
   *
   * @param stream The <code>PrintWriter</code> to write to.
   * @param indent The indentation point.
   */
  public void list(PrintWriter out, int indent)
  {
    super.list (out, indent);
    for (int i = 0; i < ncomponents; ++i)
      component[i].list (out, indent + 2);
  }


  /* The following classes are used in concert with the
     visitChildren() method to implement all the graphics operations
     that requires traversal of the containment hierarchy. */

  abstract static class GfxVisitor
  {
    public abstract void visit(Component c, Graphics gfx);
  }

  static class GfxPaintVisitor extends GfxVisitor
  {
    public void visit(Component c, Graphics gfx) { c.paint(gfx); }
    public static final GfxVisitor INSTANCE = new GfxPaintVisitor();
  }

  static class GfxPrintVisitor extends GfxVisitor
  {
    public void visit(Component c, Graphics gfx) { c.print(gfx); }
    public static final GfxVisitor INSTANCE = new GfxPrintVisitor();
  }

  static class GfxPaintAllVisitor extends GfxVisitor
  {
    public void visit(Component c, Graphics gfx) { c.paintAll(gfx); }
    public static final GfxVisitor INSTANCE = new GfxPaintAllVisitor();
  }

  static class GfxPrintAllVisitor extends GfxVisitor
  {
    public void visit(Component c, Graphics gfx) { c.printAll(gfx); }
    public static final GfxVisitor INSTANCE = new GfxPrintAllVisitor();
  }

  // This is used to implement Component.transferFocus.
  Component findNextFocusComponent (Component child)
  {
    int start, end;
    if (child != null)
      {
	for (start = 0; start < ncomponents; ++start)
	  {
	    if (component[start] == child)
	      break;
	  }
	end = start;
	// This special case lets us be sure to terminate.
	if (end == 0)
	  end = ncomponents;
	++start;
      }
    else
      {
	start = 0;
	end = ncomponents;
      }

    for (int j = start; j != end; ++j)
      {
	if (j >= ncomponents)
	  {
	    // The JCL says that we should wrap here.  However, that
	    // seems wrong.  To me it seems that focus order should be
	    // global within in given window.  So instead if we reach
	    // the end we try to look in our parent, if we have one.
	    if (parent != null)
	      return parent.findNextFocusComponent (this);
	    j -= ncomponents;
	  }
	if (component[j] instanceof Container)
	  {
	    Component c = component[j];
	    c = c.findNextFocusComponent (null);
	    if (c != null)
	      return c;
	  }
	else if (component[j].isFocusTraversable ())
	  return component[j];
      }

    return null;
  }
}