1 /*
   2  * Copyright (c) 1997, 2008, 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 javax.swing;
  26 
  27 import java.awt.event.*;
  28 import java.util.Vector;
  29 import java.util.Enumeration;
  30 import java.io.Serializable;
  31 
  32 /**
  33  * This class is used to create a multiple-exclusion scope for
  34  * a set of buttons. Creating a set of buttons with the
  35  * same <code>ButtonGroup</code> object means that
  36  * turning "on" one of those buttons
  37  * turns off all other buttons in the group.
  38  * <p>
  39  * A <code>ButtonGroup</code> can be used with
  40  * any set of objects that inherit from <code>AbstractButton</code>.
  41  * Typically a button group contains instances of
  42  * <code>JRadioButton</code>,
  43  * <code>JRadioButtonMenuItem</code>,
  44  * or <code>JToggleButton</code>.
  45  * It wouldn't make sense to put an instance of
  46  * <code>JButton</code> or <code>JMenuItem</code>
  47  * in a button group
  48  * because <code>JButton</code> and <code>JMenuItem</code>
  49  * don't implement the selected state.
  50  * <p>
  51  * Initially, all buttons in the group are unselected.
  52  * <p>
  53  * For examples and further information on using button groups see
  54  * <a href="http://java.sun.com/docs/books/tutorial/uiswing/components/button.html#radiobutton">How to Use Radio Buttons</a>,
  55  * a section in <em>The Java Tutorial</em>.
  56  * <p>
  57  * <strong>Warning:</strong>
  58  * Serialized objects of this class will not be compatible with
  59  * future Swing releases. The current serialization support is
  60  * appropriate for short term storage or RMI between applications running
  61  * the same version of Swing.  As of 1.4, support for long term storage
  62  * of all JavaBeans<sup><font size="-2">TM</font></sup>
  63  * has been added to the <code>java.beans</code> package.
  64  * Please see {@link java.beans.XMLEncoder}.
  65  *
  66  * @author Jeff Dinkins
  67  */
  68 @SuppressWarnings("serial")
  69 public class ButtonGroup implements Serializable {
  70 
  71     // the list of buttons participating in this group
  72     protected Vector<AbstractButton> buttons = new Vector<AbstractButton>();
  73 
  74     /**
  75      * The current selection.
  76      */
  77     ButtonModel selection = null;
  78 
  79     /**
  80      * Creates a new <code>ButtonGroup</code>.
  81      */
  82     public ButtonGroup() {}
  83 
  84     /**
  85      * Adds the button to the group.
  86      * @param b the button to be added
  87      */
  88     public void add(AbstractButton b) {
  89         if(b == null) {
  90             return;
  91         }
  92         buttons.addElement(b);
  93 
  94         if (b.isSelected()) {
  95             if (selection == null) {
  96                 selection = b.getModel();
  97             } else {
  98                 b.setSelected(false);
  99             }
 100         }
 101 
 102         b.getModel().setGroup(this);
 103     }
 104 
 105     /**
 106      * Removes the button from the group.
 107      * @param b the button to be removed
 108      */
 109     public void remove(AbstractButton b) {
 110         if(b == null) {
 111             return;
 112         }
 113         buttons.removeElement(b);
 114         if(b.getModel() == selection) {
 115             selection = null;
 116         }
 117         b.getModel().setGroup(null);
 118     }
 119 
 120     /**
 121      * Clears the selection such that none of the buttons
 122      * in the <code>ButtonGroup</code> are selected.
 123      *
 124      * @since 1.6
 125      */
 126     public void clearSelection() {
 127         if (selection != null) {
 128             ButtonModel oldSelection = selection;
 129             selection = null;
 130             oldSelection.setSelected(false);
 131         }
 132     }
 133 
 134     /**
 135      * Returns all the buttons that are participating in
 136      * this group.
 137      * @return an <code>Enumeration</code> of the buttons in this group
 138      */
 139     public Enumeration<AbstractButton> getElements() {
 140         return buttons.elements();
 141     }
 142 
 143     /**
 144      * Returns the model of the selected button.
 145      * @return the selected button model
 146      */
 147     public ButtonModel getSelection() {
 148         return selection;
 149     }
 150 
 151     /**
 152      * Sets the selected value for the <code>ButtonModel</code>.
 153      * Only one button in the group may be selected at a time.
 154      * @param m the <code>ButtonModel</code>
 155      * @param b <code>true</code> if this button is to be
 156      *   selected, otherwise <code>false</code>
 157      */
 158     public void setSelected(ButtonModel m, boolean b) {
 159         if (b && m != null && m != selection) {
 160             ButtonModel oldSelection = selection;
 161             selection = m;
 162             if (oldSelection != null) {
 163                 oldSelection.setSelected(false);
 164             }
 165             m.setSelected(true);
 166         }
 167     }
 168 
 169     /**
 170      * Returns whether a <code>ButtonModel</code> is selected.
 171      * @return <code>true</code> if the button is selected,
 172      *   otherwise returns <code>false</code>
 173      */
 174     public boolean isSelected(ButtonModel m) {
 175         return (m == selection);
 176     }
 177 
 178     /**
 179      * Returns the number of buttons in the group.
 180      * @return the button count
 181      * @since 1.3
 182      */
 183     public int getButtonCount() {
 184         if (buttons == null) {
 185             return 0;
 186         } else {
 187             return buttons.size();
 188         }
 189     }
 190 
 191 }