ButtonGroup


1   /*
2    * @(#)ButtonGroup.java 1.37 04/05/05
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   package javax.swing;
8   
9   import java.awt.event.*;
10  import java.util.Vector  ;
11  import java.util.Enumeration  ;
12  import java.io.Serializable  ;
13   
14  /**
15   * This class is used to create a multiple-exclusion scope for
16   * a set of buttons. Creating a set of buttons with the
17   * same <code>ButtonGroup</code> object means that
18   * turning "on" one of those buttons 
19   * turns off all other buttons in the group.
20   * <p>
21   * A <code>ButtonGroup</code> can be used with
22   * any set of objects that inherit from <code>AbstractButton</code>.
23   * Typically a button group contains instances of 
24   * <code>JRadioButton</code>,
25   * <code>JRadioButtonMenuItem</code>,
26   * or <code>JToggleButton</code>.
27   * It wouldn't make sense to put an instance of 
28   * <code>JButton</code> or <code>JMenuItem</code>
29   * in a button group
30   * because <code>JButton</code> and <code>JMenuItem</code>
31   * don't implement the selected state.
32   * <p>
33   * Initially, all buttons in the group are unselected. Once any button is
34   * selected, one button is always selected in the group. There is no way
35   * to turn a button programmatically to "off", in order to clear the button
36   * group. To give the appearance of "none selected", add an invisible radio
37   * button to the group and then programmatically select that button to 
38   * turn off all the displayed radio buttons. For example, a normal button
39   * with the label "none" could be wired to select the invisible radio button.
40   * <p>
41   * For examples and further information on using button groups see
42   * <a HREF="http://java.sun.com/docs/books/tutorial/uiswing/components/button.html#radiobutton">How to Use Radio Buttons</a>,
43   * a section in <em>The Java Tutorial</em>.
44   * <p>
45   * <strong>Warning:</strong>
46   * Serialized objects of this class will not be compatible with
47   * future Swing releases. The current serialization support is
48   * appropriate for short term storage or RMI between applications running
49   * the same version of Swing.  As of 1.4, support for long term storage
50   * of all JavaBeans<sup><font size="-2">TM</font></sup>
51   * has been added to the <code>java.beans</code> package.
52   * Please see {@link java.beans.XMLEncoder}.
53   *
54   * @version 1.37 05/05/04
55   * @author Jeff Dinkins
56   */
57  public class ButtonGroup implements Serializable   {
58  
59      // the list of buttons participating in this group
60      protected Vector  <AbstractButton  > buttons = new Vector  ();
61  
62      /**
63       * The current selection.
64       */
65      ButtonModel   selection = null;
66  
67      /**
68       * Creates a new <code>ButtonGroup</code>.
69       */
70      public ButtonGroup() {}
71  
72      /**
73       * Adds the button to the group.
74       * @param b the button to be added
75       */ 
76      public void add(AbstractButton   b) {
77          if(b == null) {
78              return;
79          }
80          buttons.addElement(b);
81  
82          if (b.isSelected()) {
83              if (selection == null) {
84                  selection = b.getModel();
85              } else {
86                  b.setSelected(false);
87              }
88          }
89  
90          b.getModel().setGroup(this);
91      }
92   
93      /**
94       * Removes the button from the group.
95       * @param b the button to be removed
96       */ 
97      public void remove(AbstractButton   b) {
98          if(b == null) {
99              return;
100         }
101         buttons.removeElement(b);
102         if(b.getModel() == selection) {
103             selection = null;
104         }
105         b.getModel().setGroup(null);
106     }
107 
108     /**
109      * Returns all the buttons that are participating in
110      * this group.
111      * @return an <code>Enumeration</code> of the buttons in this group
112      */
113     public Enumeration  <AbstractButton  > getElements() {
114         return buttons.elements();
115     }
116 
117     /**
118      * Returns the model of the selected button.
119      * @return the selected button model
120      */
121     public ButtonModel   getSelection() {
122         return selection;
123     }
124 
125     /**
126      * Sets the selected value for the <code>ButtonModel</code>.
127      * Only one button in the group may be selected at a time.
128      * @param m the <code>ButtonModel</code>
129      * @param b <code>true</code> if this button is to be
130      *   selected, otherwise <code>false</code>
131      */
132     public void setSelected(ButtonModel   m, boolean b) {
133         if (b && m != null && m != selection) {
134             ButtonModel   oldSelection = selection;
135             selection = m;
136             if (oldSelection != null) {
137                 oldSelection.setSelected(false);
138             }
139             m.setSelected(true);
140         } 
141     }
142 
143     /**
144      * Returns whether a <code>ButtonModel</code> is selected.
145      * @return <code>true</code> if the button is selected,
146      *   otherwise returns <code>false</code>
147      */
148     public boolean isSelected(ButtonModel   m) {
149         return (m == selection);
150     }
151 
152     /**
153      * Returns the number of buttons in the group.
154      * @return the button count
155      * @since 1.3
156      */
157     public int getButtonCount() {
158     if (buttons == null) {
159         return 0;
160     } else {
161         return buttons.size();
162     }
163     }
164 
165 }
166
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