1 /*
   2  * Copyright (c) 1996, 2020, 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 
  26 package java.awt.event;
  27 
  28 /**
  29  * An abstract adapter class for receiving keyboard focus events.
  30  * The methods in this class are empty. This class exists as
  31  * convenience for creating listener objects.
  32  * <P>
  33  * Extend this class to create a {@code FocusEvent} listener
  34  * and override the methods for the events of interest. (If you implement the
  35  * {@code FocusListener} interface, you have to define all of
  36  * the methods in it. This abstract class defines null methods for them
  37  * all, so you can only have to define methods for events you care about.)
  38  * <P>
  39  * Create a listener object using the extended class and then register it with
  40  * a component using the component's {@code addFocusListener}
  41  * method. When the component gains or loses the keyboard focus,
  42  * the relevant method in the listener object is invoked,
  43  * and the {@code FocusEvent} is passed to it.
  44  *
  45  * @see FocusEvent
  46  * @see FocusListener
  47  * @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/focuslistener.html">Tutorial: Writing a Focus Listener</a>
  48  *
  49  * @author Carl Quinn
  50  * @since 1.1
  51  */
  52 public abstract class FocusAdapter implements FocusListener {
  53 
  54     /**
  55      * Constructs a {@code FocusAdapter}.
  56      */
  57     protected FocusAdapter() {}
  58 
  59     /**
  60      * Invoked when a component gains the keyboard focus.
  61      */
  62     public void focusGained(FocusEvent e) {}
  63 
  64     /**
  65      * Invoked when a component loses the keyboard focus.
  66      */
  67     public void focusLost(FocusEvent e) {}
  68 }
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