1 /*
   2  * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.awt;
  26 
  27 import java.awt.event.KeyEvent;
  28 
  29 
  30 /**
  31  * A KeyEventDispatcher cooperates with the current KeyboardFocusManager in the
  32  * targeting and dispatching of all KeyEvents. KeyEventDispatchers registered
  33  * with the current KeyboardFocusManager will receive KeyEvents before they are
  34  * dispatched to their targets, allowing each KeyEventDispatcher to retarget
  35  * the event, consume it, dispatch the event itself, or make other changes.
  36  * <p>
  37  * Note that KeyboardFocusManager itself implements KeyEventDispatcher. By
  38  * default, the current KeyboardFocusManager will be the sink for all KeyEvents
  39  * not dispatched by the registered KeyEventDispatchers. The current
  40  * KeyboardFocusManager cannot be completely deregistered as a
  41  * KeyEventDispatcher. However, if a KeyEventDispatcher reports that it
  42  * dispatched the KeyEvent, regardless of whether it actually did so, the
  43  * KeyboardFocusManager will take no further action with regard to the
  44  * KeyEvent. (While it is possible for client code to register the current
  45  * KeyboardFocusManager as a KeyEventDispatcher one or more times, this is
  46  * usually unnecessary and not recommended.)
  47  *
  48  * @author David Mendenhall
  49  *
  50  * @see KeyboardFocusManager#addKeyEventDispatcher
  51  * @see KeyboardFocusManager#removeKeyEventDispatcher
  52  * @since 1.4
  53  */
  54 @FunctionalInterface
  55 public interface KeyEventDispatcher {
  56 
  57     /**
  58      * This method is called by the current KeyboardFocusManager requesting
  59      * that this KeyEventDispatcher dispatch the specified event on its behalf.
  60      * This KeyEventDispatcher is free to retarget the event, consume it,
  61      * dispatch it itself, or make other changes. This capability is typically
  62      * used to deliver KeyEvents to Components other than the focus owner. This
  63      * can be useful when navigating children of non-focusable Windows in an
  64      * accessible environment, for example. Note that if a KeyEventDispatcher
  65      * dispatches the KeyEvent itself, it must use <code>redispatchEvent</code>
  66      * to prevent the current KeyboardFocusManager from recursively requesting
  67      * that this KeyEventDispatcher dispatch the event again.
  68      * <p>
  69      * If an implementation of this method returns <code>false</code>, then
  70      * the KeyEvent is passed to the next KeyEventDispatcher in the chain,
  71      * ending with the current KeyboardFocusManager. If an implementation
  72      * returns <code>true</code>, the KeyEvent is assumed to have been
  73      * dispatched (although this need not be the case), and the current
  74      * KeyboardFocusManager will take no further action with regard to the
  75      * KeyEvent. In such a case,
  76      * <code>KeyboardFocusManager.dispatchEvent</code> should return
  77      * <code>true</code> as well. If an implementation consumes the KeyEvent,
  78      * but returns <code>false</code>, the consumed event will still be passed
  79      * to the next KeyEventDispatcher in the chain. It is important for
  80      * developers to check whether the KeyEvent has been consumed before
  81      * dispatching it to a target. By default, the current KeyboardFocusManager
  82      * will not dispatch a consumed KeyEvent.
  83      *
  84      * @param e the KeyEvent to dispatch
  85      * @return <code>true</code> if the KeyboardFocusManager should take no
  86      *         further action with regard to the KeyEvent; <code>false</code>
  87      *         otherwise
  88      * @see KeyboardFocusManager#redispatchEvent
  89      */
  90     boolean dispatchKeyEvent(KeyEvent e);
  91 }
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