/* * Copyright (c) 1995, 2008, 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 java.awt; import java.awt.peer.CheckboxPeer;import java.awt.event.*;import java.util.EventListener;import java.io.ObjectOutputStream;import java.io.ObjectInputStream;import java.io.IOException;import javax.accessibility.*;  /** * A check box is a graphical component that can be in either an * "on" (<code>true</code>) or "off" (<code>false</code>) state. * Clicking on a check box changes its state from * "on" to "off," or from "off" to "on." * <p> * The following code example creates a set of check boxes in * a grid layout: * <p> * <hr><blockquote><pre> * setLayout(new GridLayout(3, 1)); * add(new Checkbox("one", null, true)); * add(new Checkbox("two")); * add(new Checkbox("three")); * </pre></blockquote><hr> * <p> * This image depicts the check boxes and grid layout * created by this code example: * <p> * <img src="doc-files/Checkbox-1.gif" alt="The following context describes the graphic." * ALIGN=center HSPACE=10 VSPACE=7> * <p> * The button labeled <code>one</code> is in the "on" state, and the * other two are in the "off" state. In this example, which uses the * <code>GridLayout</code> class, the states of the three check * boxes are set independently. * <p> * Alternatively, several check boxes can be grouped together under * the control of a single object, using the * <code>CheckboxGroup</code> class. * In a check box group, at most one button can be in the "on" * state at any given time. Clicking on a check box to turn it on * forces any other check box in the same group that is on * into the "off" state. * * @author      Sami Shaio * @see         java.awt.GridLayout * @see         java.awt.CheckboxGroup * @since       JDK1.0 */public class Checkbox extends Component implements ItemSelectable, Accessible {     static {        /* ensure that the necessary native libraries are loaded */        Toolkit.loadLibraries();        if (!GraphicsEnvironment.isHeadless()) {            initIDs();        }    }     /**     * The label of the Checkbox.     * This field can be null.     * @serial     * @see #getLabel()     * @see #setLabel(String)     */    String label;     /**     * The state of the <code>Checkbox</code>.     * @serial     * @see #getState()     * @see #setState(boolean)     */    boolean state;     /**     * The check box group.         * This field can be null indicating that the checkbox         * is not a group checkbox.         * @serial     * @see #getCheckboxGroup()     * @see #setCheckboxGroup(CheckboxGroup)     */    CheckboxGroup group;     transient ItemListener itemListener;     private static final String base = "checkbox";    private static int nameCounter = 0;     /*     * JDK 1.1 serialVersionUID     */    private static final long serialVersionUID = 7270714317450821763L;     /**     * Helper function for setState and CheckboxGroup.setSelectedCheckbox     * Should remain package-private.     */    void setStateInternal(boolean state) {        this.state = state;        CheckboxPeer peer = (CheckboxPeer)this.peer;        if (peer != null) {            peer.setState(state);        }    }     /**     * Creates a check box with an empty string for its label.     * The state of this check box is set to "off," and it is not     * part of any check box group.     * @exception HeadlessException if GraphicsEnvironment.isHeadless()     * returns true     * @see java.awt.GraphicsEnvironment#isHeadless     */    public Checkbox() throws HeadlessException {        this("", false, null);    }     /**     * Creates a check box with the specified label.  The state     * of this check box is set to "off," and it is not part of     * any check box group.     *     * @param     label   a string label for this check box,     *                        or <code>null</code> for no label.     * @exception HeadlessException if     *      <code>GraphicsEnvironment.isHeadless</code>     *      returns <code>true</code>     * @see java.awt.GraphicsEnvironment#isHeadless     */    public Checkbox(String label) throws HeadlessException {        this(label, false, null);    }     /**     * Creates a check box with the specified label     * and sets the specified state.     * This check box is not part of any check box group.     *     * @param     label   a string label for this check box,     *                        or <code>null</code> for no label     * @param     state    the initial state of this check box     * @exception HeadlessException if     *     <code>GraphicsEnvironment.isHeadless</code>     *     returns <code>true</code>     * @see java.awt.GraphicsEnvironment#isHeadless     */    public Checkbox(String label, boolean state) throws HeadlessException {        this(label, state, null);    }     /**     * Constructs a Checkbox with the specified label, set to the     * specified state, and in the specified check box group.     *     * @param     label   a string label for this check box,     *                        or <code>null</code> for no label.     * @param     state   the initial state of this check box.     * @param     group   a check box group for this check box,     *                           or <code>null</code> for no group.     * @exception HeadlessException if     *     <code>GraphicsEnvironment.isHeadless</code>     *     returns <code>true</code>     * @see java.awt.GraphicsEnvironment#isHeadless     * @since     JDK1.1     */    public Checkbox(String label, boolean state, CheckboxGroup group)        throws HeadlessException {        GraphicsEnvironment.checkHeadless();        this.label = label;        this.state = state;        this.group = group;        if (state && (group != null)) {            group.setSelectedCheckbox(this);        }    }     /**     * Creates a check box with the specified label, in the specified     * check box group, and set to the specified state.     *     * @param     label   a string label for this check box,     *                        or <code>null</code> for no label.     * @param     group   a check box group for this check box,     *                           or <code>null</code> for no group.     * @param     state   the initial state of this check box.     * @exception HeadlessException if     *    <code>GraphicsEnvironment.isHeadless</code>     *    returns <code>true</code>     * @see java.awt.GraphicsEnvironment#isHeadless     * @since     JDK1.1     */    public Checkbox(String label, CheckboxGroup group, boolean state)        throws HeadlessException {        this(label, state, group);    }     /**     * Constructs a name for this component.  Called by     * <code>getName</code> when the name is <code>null</code>.     *     * @return a name for this component     */    String constructComponentName() {        synchronized (Checkbox.class) {            return base + nameCounter++;        }    }     /**     * Creates the peer of the Checkbox. The peer allows you to change the     * look of the Checkbox without changing its functionality.     *     * @see     java.awt.Toolkit#createCheckbox(java.awt.Checkbox)     * @see     java.awt.Component#getToolkit()     */    public void addNotify() {        synchronized (getTreeLock()) {            if (peer == null)                peer = getToolkit().createCheckbox(this);            super.addNotify();        }    }     /**     * Gets the label of this check box.     *     * @return   the label of this check box, or <code>null</code>     *                  if this check box has no label.     * @see      #setLabel(String)     */    public String getLabel() {        return label;    }     /**     * Sets this check box's label to be the string argument.     *     * @param    label   a string to set as the new label, or     *                        <code>null</code> for no label.     * @see      #getLabel     */    public void setLabel(String label) {        boolean testvalid = false;         synchronized (this) {            if (label != this.label && (this.label == null ||                                        !this.label.equals(label))) {                this.label = label;                CheckboxPeer peer = (CheckboxPeer)this.peer;                if (peer != null) {                    peer.setLabel(label);                }                testvalid = true;            }        }         // This could change the preferred size of the Component.        if (testvalid) {            invalidateIfValid();        }    }     /**     * Determines whether this check box is in the "on" or "off" state.     * The boolean value <code>true</code> indicates the "on" state,     * and <code>false</code> indicates the "off" state.     *     * @return    the state of this check box, as a boolean value     * @see       #setState     */    public boolean getState() {        return state;    }     /**     * Sets the state of this check box to the specified state.     * The boolean value <code>true</code> indicates the "on" state,     * and <code>false</code> indicates the "off" state.     *     * <p>Note that this method should be primarily used to     * initialize the state of the checkbox.  Programmatically     * setting the state of the checkbox will <i>not</i> trigger     * an <code>ItemEvent</code>.  The only way to trigger an     * <code>ItemEvent</code> is by user interaction.     *     * @param     state   the boolean state of the check box     * @see       #getState     */    public void setState(boolean state) {        /* Cannot hold check box lock when calling group.setSelectedCheckbox. */        CheckboxGroup group = this.group;        if (group != null) {            if (state) {                group.setSelectedCheckbox(this);            } else if (group.getSelectedCheckbox() == this) {                state = true;            }        }        setStateInternal(state);    }     /**     * Returns an array (length 1) containing the checkbox     * label or null if the checkbox is not selected.     * @see ItemSelectable     */    public Object[] getSelectedObjects() {        if (state) {            Object[] items = new Object[1];            items[0] = label;            return items;        }        return null;    }     /**     * Determines this check box's group.     * @return     this check box's group, or <code>null</code>     *               if the check box is not part of a check box group.     * @see        #setCheckboxGroup(CheckboxGroup)     */    public CheckboxGroup getCheckboxGroup() {        return group;    }     /**     * Sets this check box's group to the specified check box group.     * If this check box is already in a different check box group,     * it is first taken out of that group.     * <p>     * If the state of this check box is <code>true</code> and the new     * group already has a check box selected, this check box's state     * is changed to <code>false</code>.  If the state of this check     * box is <code>true</code> and the new group has no check box     * selected, this check box becomes the selected checkbox for     * the new group and its state is <code>true</code>.     *     * @param     g   the new check box group, or <code>null</code>     *                to remove this check box from any check box group     * @see       #getCheckboxGroup     */    public void setCheckboxGroup(CheckboxGroup g) {        CheckboxGroup oldGroup;        boolean oldState;         /* Do nothing if this check box has already belonged         * to the check box group g.         */        if (this.group == g) {            return;        }         synchronized (this) {            oldGroup = this.group;            oldState = getState();             this.group = g;            CheckboxPeer peer = (CheckboxPeer)this.peer;            if (peer != null) {                peer.setCheckboxGroup(g);            }            if (this.group != null && getState()) {                if (this.group.getSelectedCheckbox() != null) {                    setState(false);                } else {                    this.group.setSelectedCheckbox(this);                }            }        }         /* Locking check box below could cause deadlock with         * CheckboxGroup's setSelectedCheckbox method.         *         * Fix for 4726853 by kdm@sparc.spb.su         * Here we should check if this check box was selected         * in the previous group and set selected check box to         * null for that group if so.         */        if (oldGroup != null && oldState) {            oldGroup.setSelectedCheckbox(null);        }    }     /**     * Adds the specified item listener to receive item events from     * this check box.  Item events are sent to listeners in response     * to user input, but not in response to calls to setState().     * If l is null, no exception is thrown and no action is performed.     * <p>Refer to <a href="doc-files/AWTThreadIssues.html#ListenersThreads"     * >AWT Threading Issues</a> for details on AWT's threading model.     *     * @param         l    the item listener     * @see           #removeItemListener     * @see           #getItemListeners     * @see           #setState     * @see           java.awt.event.ItemEvent     * @see           java.awt.event.ItemListener     * @since         JDK1.1     */    public synchronized void addItemListener(ItemListener l) {        if (l == null) {            return;        }        itemListener = AWTEventMulticaster.add(itemListener, l);        newEventsOnly = true;    }     /**     * Removes the specified item listener so that the item listener     * no longer receives item events from this check box.     * If l is null, no exception is thrown and no action is performed.     * <p>Refer to <a href="doc-files/AWTThreadIssues.html#ListenersThreads"     * >AWT Threading Issues</a> for details on AWT's threading model.     *     * @param         l    the item listener     * @see           #addItemListener     * @see           #getItemListeners     * @see           java.awt.event.ItemEvent     * @see           java.awt.event.ItemListener     * @since         JDK1.1     */    public synchronized void removeItemListener(ItemListener l) {        if (l == null) {            return;        }        itemListener = AWTEventMulticaster.remove(itemListener, l);    }     /**     * Returns an array of all the item listeners     * registered on this checkbox.     *     * @return all of this checkbox's <code>ItemListener</code>s     *         or an empty array if no item     *         listeners are currently registered     *     * @see           #addItemListener     * @see           #removeItemListener     * @see           java.awt.event.ItemEvent     * @see           java.awt.event.ItemListener     * @since 1.4     */    public synchronized ItemListener[] getItemListeners() {        return (ItemListener[]) (getListeners(ItemListener.class));    }     /**     * Returns an array of all the objects currently registered     * as <code><em>Foo</em>Listener</code>s     * upon this <code>Checkbox</code>.     * <code><em>Foo</em>Listener</code>s are registered using the     * <code>add<em>Foo</em>Listener</code> method.     *     * <p>     * You can specify the <code>listenerType</code> argument     * with a class literal, such as     * <code><em>Foo</em>Listener.class</code>.     * For example, you can query a     * <code>Checkbox</code> <code>c</code>     * for its item listeners with the following code:     *     * <pre>ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.class));</pre>     *     * If no such listeners exist, this method returns an empty array.     *     * @param listenerType the type of listeners requested; this parameter     *          should specify an interface that descends from     *          <code>java.util.EventListener</code>     * @return an array of all objects registered as     *          <code><em>Foo</em>Listener</code>s on this checkbox,     *          or an empty array if no such

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