/*
* Copyright (c) 2000, 2005, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.awt;
/**
* A FocusTraversalPolicy defines the order in which Components with a
* particular focus cycle root are traversed. Instances can apply the policy to
* arbitrary focus cycle roots, allowing themselves to be shared across
* Containers. They do not need to be reinitialized when the focus cycle roots
* of a Component hierarchy change.
* <p>
* The core responsibility of a FocusTraversalPolicy is to provide algorithms
* determining the next and previous Components to focus when traversing
* forward or backward in a UI. Each FocusTraversalPolicy must also provide
* algorithms for determining the first, last, and default Components in a
* traversal cycle. First and last Components are used when normal forward and
* backward traversal, respectively, wraps. The default Component is the first
* to receive focus when traversing down into a new focus traversal cycle.
* A FocusTraversalPolicy can optionally provide an algorithm for determining
* a Window's initial Component. The initial Component is the first to receive
* focus when a Window is first made visible.
* <p>
* FocusTraversalPolicy takes into account <a
* href="doc-files/FocusSpec.html#FocusTraversalPolicyProviders">focus traversal
* policy providers</a>. When searching for first/last/next/previous Component,
* if a focus traversal policy provider is encountered, its focus traversal
* policy is used to perform the search operation.
* <p>
* Please see
* <a href="http://java.sun.com/docs/books/tutorial/uiswing/misc/focus.html">
* How to Use the Focus Subsystem</a>,
* a section in <em>The Java Tutorial</em>, and the
* <a href="../../java/awt/doc-files/FocusSpec.html">Focus Specification</a>
* for more information.
*
* @author David Mendenhall
*
* @see Container#setFocusTraversalPolicy
* @see Container#getFocusTraversalPolicy
* @see Container#setFocusCycleRoot
* @see Container#isFocusCycleRoot
* @see Container#setFocusTraversalPolicyProvider
* @see Container#isFocusTraversalPolicyProvider
* @see KeyboardFocusManager#setDefaultFocusTraversalPolicy
* @see KeyboardFocusManager#getDefaultFocusTraversalPolicy
* @since 1.4
*/
public abstract class FocusTraversalPolicy {
/**
* Returns the Component that should receive the focus after aComponent.
* aContainer must be a focus cycle root of aComponent or a focus traversal
* policy provider.
*
* @param aContainer a focus cycle root of aComponent or focus traversal
* policy provider
* @param aComponent a (possibly indirect) child of aContainer, or
* aContainer itself
* @return the Component that should receive the focus after aComponent, or
* null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is not a focus cycle
* root of aComponent or a focus traversal policy provider, or if
* either aContainer or aComponent is null
*/
public abstract Component getComponentAfter(Container aContainer,
Component aComponent);
/**
* Returns the Component that should receive the focus before aComponent.
* aContainer must be a focus cycle root of aComponent or a focus traversal
* policy provider.
*
* @param aContainer a focus cycle root of aComponent or focus traversal
* policy provider
* @param aComponent a (possibly indirect) child of aContainer, or
* aContainer itself
* @return the Component that should receive the focus before aComponent,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is not a focus cycle
* root of aComponent or a focus traversal policy provider, or if
* either aContainer or aComponent is null
*/
public abstract Component getComponentBefore(Container aContainer,
Component aComponent);
/**
* Returns the first Component in the traversal cycle. This method is used
* to determine the next Component to focus when traversal wraps in the
* forward direction.
*
* @param aContainer the focus cycle root or focus traversal policy provider
* whose first Component is to be returned
* @return the first Component in the traversal cycle of aContainer,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is null
*/
public abstract Component getFirstComponent(Container aContainer);
/**
* Returns the last Component in the traversal cycle. This method is used
* to determine the next Component to focus when traversal wraps in the
* reverse direction.
*
* @param aContainer the focus cycle root or focus traversal policy
* provider whose last Component is to be returned
* @return the last Component in the traversal cycle of aContainer,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is null
*/
public abstract Component getLastComponent(Container aContainer);
/**
* Returns the default Component to focus. This Component will be the first
* to receive focus when traversing down into a new focus traversal cycle
* rooted at aContainer.
*
* @param aContainer the focus cycle root or focus traversal policy
* provider whose default Component is to be returned
* @return the default Component in the traversal cycle of aContainer,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is null
*/
public abstract Component getDefaultComponent(Container aContainer);
/**
* Returns the Component that should receive the focus when a Window is
* made visible for the first time. Once the Window has been made visible
* by a call to <code>show()</code> or <code>setVisible(true)</code>, the
* initial Component will not be used again. Instead, if the Window loses
* and subsequently regains focus, or is made invisible or undisplayable
* and subsequently made visible and displayable, the Window's most
* recently focused Component will become the focus owner. The default
* implementation of this method returns the default Component.
*
* @param window the Window whose initial Component is to be returned
* @return the Component that should receive the focus when window is made
* visible for the first time, or null if no suitable Component can
* be found
* @see #getDefaultComponent
* @see Window#getMostRecentFocusOwner
* @throws IllegalArgumentException if window is null
*/
public Component getInitialComponent(Window window) {
if ( window == null ){
throw new IllegalArgumentException("window cannot be equal to null.");
}
Component def = getDefaultComponent(window);
if (def == null && window.isFocusableWindow()) {
def = window;
}
return def;
}
}