java/awt/ContainerOrderFocusTraversalPolicy.java

/* ContainerOrderFocusTraversalPolicy.java --
   Copyright (C) 2002, 2005  Free Software Foundation, Inc.

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package java.awt;

import java.io.Serializable;

/**
 * ContainerOrderFocusTraversalPolicy defines a focus traversal order
 * based on the order in which Components were packed in a Container.
 * This policy performs a pre-order traversal of the Component
 * hierarchy starting from a given focus cycle root.  Portions of the
 * hierarchy that are not visible and displayable are skipped.
 *
 * By default, this policy transfers focus down-cycle implicitly.
 * That is, if a forward traversal is requested on a focus cycle root
 * and the focus cycle root has focusable children, the focus will
 * automatically be transfered down to the lower focus cycle.
 *
 * The default implementation of accept accepts only Components that
 * are visible, displayable, enabled and focusable.  Derived classes
 * can override these acceptance criteria by overriding accept.
 *
 * @author Michael Koch
 * @author Thomas Fitzsimmons (fitzsim@redhat.com)
 * @since 1.4
 */
public class ContainerOrderFocusTraversalPolicy extends FocusTraversalPolicy
  implements Serializable
{
  /**
   * Compatible to JDK 1.4+
   */
  static final long serialVersionUID = 486933713763926351L;

  /**
   * True if implicit down cycling is enabled.
   */
  private boolean implicitDownCycleTraversal = true;

  /**
   * Creates the <code>ContainerOrderFocusTraversalPolicy</code> object.
   */
  public ContainerOrderFocusTraversalPolicy ()
  {
    // Nothing to do here
  }

  /**
   * Returns the Component that should receive the focus after current.
   * root must be a focus cycle root of current.
   *
   * @param root a focus cycle root of current
   * @param current a (possibly indirect) child of root, or root itself
   *
   * @return the next Component in the focus traversal order for root,
   * or null if no acceptable Component exists.
   *
   * @exception IllegalArgumentException If root is not a focus cycle
   * root of current, or if either root or current is null.
   */
  public Component getComponentAfter (Container root, Component current)
  {
    if (root == null)
      throw new IllegalArgumentException ("focus cycle root is null");
    if (current == null)
      throw new IllegalArgumentException ("current component is null");

    if (!root.isFocusCycleRoot ())
      throw new IllegalArgumentException ("root is not a focus cycle root");

    Container ancestor = current.getFocusCycleRootAncestor ();
    Container prevAncestor = ancestor;
    while (ancestor != root)
      {
	ancestor = current.getFocusCycleRootAncestor ();
	if (ancestor == prevAncestor)
	  {
	    // We've reached the top focus cycle root ancestor.  Check
	    // if it is root.
	    if (ancestor != root)
	      throw new IllegalArgumentException ("the given container is not"
						  + " a focus cycle root of the"
						  + " current component");
	    else
	      break;
	  }
	prevAncestor = ancestor;
      }

    // FIXME: is this the right thing to do here? It moves the context
    // for traversal up one focus traversal cycle.  We'll need a test
    // for this.
    if ((Component) root == current)
      root = current.getFocusCycleRootAncestor ();

    // Check if we've reached the top of the component hierarchy.  If
    // so then we want to loop around to the first component in the
    // focus traversal cycle.
    if (current instanceof Window)
      return getFirstComponent ((Container) current);

    Container parent = current.getParent ();

    synchronized (parent.getTreeLock ())
      {
        Component[] components = parent.getComponents ();
        int componentIndex = 0;
        int numComponents = parent.getComponentCount ();

        // Find component's index.
        for (int i = 0; i < numComponents; i++)
          {
            if (components[i] == current)
              componentIndex = i;
          }

        // Search forward for the next acceptable component.
        for (int i = componentIndex + 1; i < numComponents; i++)
          {
            if (accept (components[i]))
              return components[i];

            if (components[i] instanceof Container)
              {
                Component result = getFirstComponent ((Container) components[i]);

                if (result != null
                    && implicitDownCycleTraversal)
                  return result;
              }
          }

        // No focusable components after current in its Container.  So go
        // to the next Component after current's Container (parent).
        Component result = getComponentAfter (root, parent);

        return result;
      }
  }

  /**
   * Returns the Component that should receive the focus before
   * <code>current</code>.  <code>root</code> must be a focus cycle
   * root of current.
   *
   * @param root a focus cycle root of current
   * @param current a (possibly indirect) child of root, or root itself
   *
   * @return the previous Component in the focus traversal order for
   * root, or null if no acceptable Component exists.
   *
   * @exception IllegalArgumentException If root is not a focus cycle
   * root of current, or if either root or current is null.
   */
  public Component getComponentBefore (Container root, Component current)
  {
    if (root == null)
      throw new IllegalArgumentException ("focus cycle root is null");
    if (current == null)
      throw new IllegalArgumentException ("current component is null");

    if (!root.isFocusCycleRoot ())
      throw new IllegalArgumentException ("root is not a focus cycle root");

    Container ancestor = current.getFocusCycleRootAncestor ();
    Container prevAncestor = ancestor;
    while (ancestor != root)
      {
	ancestor = current.getFocusCycleRootAncestor ();
	if (ancestor == prevAncestor)
	  {
	    // We've reached the top focus cycle root ancestor.  Check
	    // if it is root.
	    if (ancestor != root)
	      throw new IllegalArgumentException ("the given container is not"
						  + " a focus cycle root of the"
						  + " current component");
	    else
	      break;
	  }
	prevAncestor = ancestor;
      }

    // FIXME: is this the right thing to do here? It moves the context
    // for traversal up one focus traversal cycle.  We'll need a test
    // for this.
    if ((Component) root == current)
      root = current.getFocusCycleRootAncestor ();

    // Check if we've reached the top of the component hierarchy.  If
    // so then we want to loop around to the last component in the
    // focus traversal cycle.
    if (current instanceof Window)
      return getLastComponent ((Container) current);

    Container parent = current.getParent ();

    synchronized (parent.getTreeLock ())
      {
        Component[] components = parent.getComponents ();
        int componentIndex = 0;
        int numComponents = parent.getComponentCount ();

        // Find component's index.
        for (int i = 0; i < numComponents; i++)
          {
            if (components[i] == current)
              componentIndex = i;
          }

        // Search backward for the next acceptable component.
        for (int i = componentIndex - 1; i >= 0; i--)
          {
            if (accept (components[i]))
              return components[i];

            if (components[i] instanceof Container)
              {
                Component result = getLastComponent ((Container) components[i]);

                if (result != null)
                  return result;
              }
          }

        // No focusable components before current in its Container.  So go
        // to the previous Component before current's Container (parent).
        Component result = getComponentBefore (root, parent);

        return result;
      }
  }

  /**
   * Returns the first Component of root that should receive the focus.
   *
   * @param root a focus cycle root
   *
   * @return the first Component in the focus traversal order for
   * root, or null if no acceptable Component exists.
   *
   * @exception IllegalArgumentException If root is null.
   */
  public Component getFirstComponent(Container root)
  {
    if (root == null)
      throw new IllegalArgumentException ();

    if (!root.isVisible ()
        || !root.isDisplayable ())
      return null;

    if (accept (root))
      return root;

    Component[] componentArray = root.getComponents ();

    for (int i = 0; i < componentArray.length; i++)
      {
        Component component = componentArray [i];

	if (accept (component))
	  return component;

        if (component instanceof Container)
          {
            Component result = getFirstComponent ((Container) component);

            if (result != null)
              return result;
          }
      }

    return null;
  }

  /**
   * Returns the last Component of root that should receive the focus.
   *
   * @param root a focus cycle root
   *
   * @return the last Component in the focus traversal order for
   * root, or null if no acceptable Component exists.
   *
   * @exception IllegalArgumentException If root is null.
   */
  public Component getLastComponent (Container root)
  {
    if (root == null)
      throw new IllegalArgumentException ();

    if (!root.isVisible ()
        || !root.isDisplayable ())
      return null;

    if (accept (root))
      return root;

    Component[] componentArray = root.getComponents ();

    for (int i = componentArray.length - 1; i >= 0; i--)
      {
        Component component = componentArray [i];

	if (accept (component))
	  return component;

        if (component instanceof Container)
          {
            Component result = getLastComponent ((Container) component);

            if (result != null)
              return result;
          }
      }

    return null;
  }

  /**
   * Returns the default Component of root that should receive the focus.
   *
   * @param root a focus cycle root
   *
   * @return the default Component in the focus traversal order for
   * root, or null if no acceptable Component exists.
   *
   * @exception IllegalArgumentException If root is null.
   */
  public Component getDefaultComponent (Container root)
  {
    return getFirstComponent (root);
  }

  /**
   * Set whether or not implicit down cycling is enabled.  If it is,
   * then initiating a forward focus traversal operation onto a focus
   * cycle root, the focus will be implicitly transferred into the
   * root container's focus cycle.
   *
   * @param value the setting for implicit down cycling
   */
  public void setImplicitDownCycleTraversal (boolean value)
  {
    implicitDownCycleTraversal = value;
  }

  /**
   * Check whether or not implicit down cycling is enabled.  If it is,
   * then initiating a forward focus traversal operation onto a focus
   * cycle root, the focus will be implicitly transferred into the
   * root container's focus cycle.
   *
   * @return true if the focus will be transferred down-cycle
   * implicitly
   */
  public boolean getImplicitDownCycleTraversal ()
  {
    return implicitDownCycleTraversal;
  }

  /**
   * Check whether the given Component is an acceptable target for the
   * keyboard input focus.
   *
   * @param current the Component to check
   *
   * @return true if current is acceptable, false otherwise
   */
  protected boolean accept (Component current)
  {
    return (current.visible
            && current.isDisplayable ()
            && current.enabled
            && current.focusable);
  }
}