Java tutorial
/* * Copyright (c) 1997, 2015, 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 javax.swing; import java.awt.event.*; import java.util.Vector; import java.util.Enumeration; import java.io.Serializable; /** * This class is used to create a multiple-exclusion scope for * a set of buttons. Creating a set of buttons with the * same <code>ButtonGroup</code> object means that * turning "on" one of those buttons * turns off all other buttons in the group. * <p> * A <code>ButtonGroup</code> can be used with * any set of objects that inherit from <code>AbstractButton</code>. * Typically a button group contains instances of * <code>JRadioButton</code>, * <code>JRadioButtonMenuItem</code>, * or <code>JToggleButton</code>. * It wouldn't make sense to put an instance of * <code>JButton</code> or <code>JMenuItem</code> * in a button group * because <code>JButton</code> and <code>JMenuItem</code> * don't implement the selected state. * <p> * Initially, all buttons in the group are unselected. * <p> * For examples and further information on using button groups see * <a href="https://docs.oracle.com/javase/tutorial/uiswing/components/button.html#radiobutton">How to Use Radio Buttons</a>, * a section in <em>The Java Tutorial</em>. * <p> * <strong>Warning:</strong> * Serialized objects of this class will not be compatible with * future Swing releases. The current serialization support is * appropriate for short term storage or RMI between applications running * the same version of Swing. As of 1.4, support for long term storage * of all JavaBeans™ * has been added to the <code>java.beans</code> package. * Please see {@link java.beans.XMLEncoder}. * * @author Jeff Dinkins * @since 1.2 */ @SuppressWarnings("serial") public class ButtonGroup implements Serializable { /** * The list of buttons participating in this group. */ protected Vector<AbstractButton> buttons = new Vector<AbstractButton>(); /** * The current selection. */ ButtonModel selection = null; /** * Creates a new <code>ButtonGroup</code>. */ public ButtonGroup() { } /** * Adds the button to the group. * @param b the button to be added */ public void add(AbstractButton b) { if (b == null) { return; } buttons.addElement(b); if (b.isSelected()) { if (selection == null) { selection = b.getModel(); } else { b.setSelected(false); } } b.getModel().setGroup(this); } /** * Removes the button from the group. * @param b the button to be removed */ public void remove(AbstractButton b) { if (b == null) { return; } buttons.removeElement(b); if (b.getModel() == selection) { selection = null; } b.getModel().setGroup(null); } /** * Clears the selection such that none of the buttons * in the <code>ButtonGroup</code> are selected. * * @since 1.6 */ public void clearSelection() { if (selection != null) { ButtonModel oldSelection = selection; selection = null; oldSelection.setSelected(false); } } /** * Returns all the buttons that are participating in * this group. * @return an <code>Enumeration</code> of the buttons in this group */ public Enumeration<AbstractButton> getElements() { return buttons.elements(); } /** * Returns the model of the selected button. * @return the selected button model */ public ButtonModel getSelection() { return selection; } /** * Sets the selected value for the <code>ButtonModel</code>. * Only one button in the group may be selected at a time. * @param m the <code>ButtonModel</code> * @param b <code>true</code> if this button is to be * selected, otherwise <code>false</code> */ public void setSelected(ButtonModel m, boolean b) { if (b && m != null && m != selection) { ButtonModel oldSelection = selection; selection = m; if (oldSelection != null) { oldSelection.setSelected(false); } m.setSelected(true); } } /** * Returns whether a {@code ButtonModel} is selected. * * @param m an isntance of {@code ButtonModel} * @return {@code true} if the button is selected, * otherwise returns {@code false} */ public boolean isSelected(ButtonModel m) { return (m == selection); } /** * Returns the number of buttons in the group. * @return the button count * @since 1.3 */ public int getButtonCount() { if (buttons == null) { return 0; } else { return buttons.size(); } } }