src/java.desktop/share/classes/javax/swing/ButtonGroup.java

/*
 * 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
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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 instance 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();
        }
    }

}