/* * 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.ButtonPeer;import java.util.EventListener;import java.awt.event.*;import java.io.ObjectOutputStream;import java.io.ObjectInputStream;import java.io.IOException;import javax.accessibility.*; /** * This class creates a labeled button. The application can cause * some action to happen when the button is pushed. This image * depicts three views of a "<code>Quit</code>" button as it appears * under the Solaris operating system: * <p> * <img src="doc-files/Button-1.gif" alt="The following context describes the graphic" * ALIGN=center HSPACE=10 VSPACE=7> * <p> * The first view shows the button as it appears normally. * The second view shows the button * when it has input focus. Its outline is darkened to let the * user know that it is an active object. The third view shows the * button when the user clicks the mouse over the button, and thus * requests that an action be performed. * <p> * The gesture of clicking on a button with the mouse * is associated with one instance of <code>ActionEvent</code>, * which is sent out when the mouse is both pressed and released * over the button. If an application is interested in knowing * when the button has been pressed but not released, as a separate * gesture, it can specialize <code>processMouseEvent</code>, * or it can register itself as a listener for mouse events by * calling <code>addMouseListener</code>. Both of these methods are * defined by <code>Component</code>, the abstract superclass of * all components. * <p> * When a button is pressed and released, AWT sends an instance * of <code>ActionEvent</code> to the button, by calling * <code>processEvent</code> on the button. The button's * <code>processEvent</code> method receives all events * for the button; it passes an action event along by * calling its own <code>processActionEvent</code> method. * The latter method passes the action event on to any action * listeners that have registered an interest in action * events generated by this button. * <p> * If an application wants to perform some action based on * a button being pressed and released, it should implement * <code>ActionListener</code> and register the new listener * to receive events from this button, by calling the button's * <code>addActionListener</code> method. The application can * make use of the button's action command as a messaging protocol. * * @author      Sami Shaio * @see         java.awt.event.ActionEvent * @see         java.awt.event.ActionListener * @see         java.awt.Component#processMouseEvent * @see         java.awt.Component#addMouseListener * @since       JDK1.0 */public class Button extends Component implements Accessible {     /**     * The button's label.  This value may be null.     * @serial     * @see #getLabel()     * @see #setLabel(String)     */    String label;     /**     * The action to be performed once a button has been     * pressed.  This value may be null.     * @serial     * @see #getActionCommand()     * @see #setActionCommand(String)     */    String actionCommand;     transient ActionListener actionListener;     private static final String base = "button";    private static int nameCounter = 0;     /*     * JDK 1.1 serialVersionUID     */    private static final long serialVersionUID = -8774683716313001058L;      static {        /* ensure that the necessary native libraries are loaded */        Toolkit.loadLibraries();        if (!GraphicsEnvironment.isHeadless()) {            initIDs();        }    }     /**     * Initialize JNI field and method IDs for fields that may be     * accessed from C.     */    private static native void initIDs();     /**     * Constructs a button with an empty string for its label.     *     * @exception HeadlessException if GraphicsEnvironment.isHeadless()     * returns true     * @see java.awt.GraphicsEnvironment#isHeadless     */    public Button() throws HeadlessException {        this("");    }     /**     * Constructs a button with the specified label.     *     * @param label  a string label for the button, or     *               <code>null</code> for no label     * @exception HeadlessException if GraphicsEnvironment.isHeadless()     * returns true     * @see java.awt.GraphicsEnvironment#isHeadless     */    public Button(String label) throws HeadlessException {        GraphicsEnvironment.checkHeadless();        this.label = label;    }     /**     * Construct a name for this component.  Called by getName() when the     * name is null.     */    String constructComponentName() {        synchronized (Button.class) {            return base + nameCounter++;        }    }     /**     * Creates the peer of the button.  The button's peer allows the     * application to change the look of the button without changing     * its functionality.     *     * @see     java.awt.Toolkit#createButton(java.awt.Button)     * @see     java.awt.Component#getToolkit()     */    public void addNotify() {        synchronized(getTreeLock()) {            if (peer == null)                peer = getToolkit().createButton(this);            super.addNotify();        }    }     /**     * Gets the label of this button.     *     * @return    the button's label, or <code>null</code>     *                if the button has no label.     * @see       java.awt.Button#setLabel     */    public String getLabel() {        return label;    }     /**     * Sets the button's label to be the specified string.     *     * @param     label   the new label, or <code>null</code>     *                if the button has no label.     * @see       java.awt.Button#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;                ButtonPeer peer = (ButtonPeer)this.peer;                if (peer != null) {                    peer.setLabel(label);                }                testvalid = true;            }        }         // This could change the preferred size of the Component.        if (testvalid) {            invalidateIfValid();        }    }     /**     * Sets the command name for the action event fired     * by this button. By default this action command is     * set to match the label of the button.     *     * @param     command  a string used to set the button's     *                  action command.     *            If the string is <code>null</code> then the action command     *            is set to match the label of the button.     * @see       java.awt.event.ActionEvent     * @since     JDK1.1     */    public void setActionCommand(String command) {        actionCommand = command;    }     /**     * Returns the command name of the action event fired by this button.     * If the command name is <code>null</code> (default) then this method     * returns the label of the button.     */    public String getActionCommand() {        return (actionCommand == null? label : actionCommand);    }     /**     * Adds the specified action listener to receive action events from     * this button. Action events occur when a user presses or releases     * the mouse over this button.     * 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 action listener     * @see           #removeActionListener     * @see           #getActionListeners     * @see           java.awt.event.ActionListener     * @since         JDK1.1     */    public synchronized void addActionListener(ActionListener l) {        if (l == null) {            return;        }        actionListener = AWTEventMulticaster.add(actionListener, l);        newEventsOnly = true;    }     /**     * Removes the specified action listener so that it no longer     * receives action events from this button. Action events occur     * when a user presses or releases the mouse over this button.     * 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 action listener     * @see             #addActionListener     * @see             #getActionListeners     * @see             java.awt.event.ActionListener     * @since           JDK1.1     */    public synchronized void removeActionListener(ActionListener l) {        if (l == null) {            return;        }        actionListener = AWTEventMulticaster.remove(actionListener, l);    }     /**     * Returns an array of all the action listeners     * registered on this button.     *     * @return all of this button's <code>ActionListener</code>s     *         or an empty array if no action     *         listeners are currently registered     *     * @see             #addActionListener     * @see             #removeActionListener     * @see             java.awt.event.ActionListener     * @since 1.4     */    public synchronized ActionListener[] getActionListeners() {        return (ActionListener[]) (getListeners(ActionListener.class));    }     /**     * Returns an array of all the objects currently registered     * as <code><em>Foo</em>Listener</code>s     * upon this <code>Button</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>Button</code> <code>b</code>     * for its action listeners with the following code:     *     * <pre>ActionListener[] als = (ActionListener[])(b.getListeners(ActionListener.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 button,     *          or an empty array if no such     *          listeners have been added     * @exception ClassCastException if <code>listenerType</code>     *          doesn't specify a class or interface that implements     *          <code>java.util.EventListener</code>     *     * @see #getActionListeners     * @since 1.3     */    public <T extends EventListener> T[] getListeners(Class<T> listenerType) {        EventListener l = null;        if  (listenerType == ActionListener.class) {            l = actionListener;        } else {            return super.getListeners(listenerType);        }        return AWTEventMulticaster.getListeners(l, listenerType);    }     // REMIND: remove when filtering is done at lower level    boolean eventEnabled(AWTEvent e) {        if (e.id == ActionEvent.ACTION_PERFORMED) {            if ((eventMask & AWTEvent.ACTION_EVENT_MASK) != 0 ||                actionListener != null) {                return true;            }            return false;        }        return super.eventEnabled(e);    }     /**     * Processes events on this button. If an event is     * an instance of <code>ActionEvent</code>, this method invokes     * the <code>processActionEvent</code> method. Otherwise,     * it invokes <code>processEvent</code> on the superclass.     * <p>Note that if the event parameter is <code>null</code>     * the behavior is unspecified and may result in an     * exception.     *     * @param        e the event     * @see          java.awt.event.ActionEvent     * @see          java.awt.Button#processActionEvent     * @since        JDK1.1     */    protected void processEvent(AWTEvent e) {        if (e instanceof ActionEvent) {            processActionEvent((ActionEvent)e);            return;        }        super.processEvent(e);    }     /**     * Processes action events occurring on this button     * by dispatching them to any registered     * <code>ActionListener</code> objects.     * <p>     * This method is not called unless action events are     * enabled for this button. Action events are enabled     * when one of the following occurs:     * <p><ul>     * <li>An <code>ActionListener</code> object is registered     * via <code>addActionListener</code>.     * <li>Action events are enabled via <code>enableEvents</code>.     * </ul>     * <p>Note that if the event parameter is <code>null</code>     * the behavior is unspecified and may result in an     * exception.     *     * @param       e the action event     * @see         java.awt.event.ActionListener     * @see         java.awt.Button#addActionListener     * @see         java.awt.Component#enableEvents     * @since       JDK1.1     */    protected void processActionEvent(ActionEvent e) {        ActionListener listener = actionListener;        if (listener != null) {            listener.actionPerformed(e);        }    }     /**     * Returns a string representing the state of this <code>Button</code>.     * This method is intended to be used only for debugging purposes, and the     * content and format of the returned string may vary between     * implementations. The returned string may be empty but may not be     * <code>null</code>.     *     * @return     the parameter string of this button     */    protected String paramString() {        return super.paramString() + ",label=" + label;    }      /* Serialization support.     */     /*     * Button Serial Data Version.     * @serial     */    private int buttonSerializedDataVersion = 1;     /**     * Writes default serializable fields to stream.  Writes     * a list of serializable <code>ActionListeners</code>     * as optional data.  The non-serializable     * <code>ActionListeners</code> are detected and     * no attempt is made to serialize them.     *     * @serialData <code>null</code> terminated sequence of 0 or     *   more pairs: the pair consists of a <code>String</code>     *   and an <code>Object</code>; the <code>String</code>     *   indicates the type of object and is one of the following:     *   <code>actionListenerK</code> indicating an     *     <code>ActionListener</code> object     *     * @param s the <code>ObjectOutputStream</code> to write     * @see AWTEventMulticaster#save(ObjectOutputStream, String, EventListener)     * @see java.awt.Component#actionListenerK     * @see #readObject(ObjectInputStream)     */    private void writeObject(ObjectOutputStream s)      throws IOException    {      s.defaultWriteObject();       AWTEventMulticaster.save(s, actionListenerK, actionListener);      s.writeObject(null);    }     /**     * Reads the <code>ObjectInputStream</code> and if     * it isn't <code>null</code> adds a listener to     * receive action events fired by the button.     * Unrecognized keys or values will be ignored.     *     * @param s the <code>ObjectInputStream</code> to read     * @exception HeadlessException if     *   <code>GraphicsEnvironment.isHeadless</code> returns     *   <code>true</code>     * @serial     * @see #removeActionListener(ActionListener)     * @see #addActionListener(ActionListener)     * @see java.awt.GraphicsEnvironment#isHeadless     * @see #writeObject(ObjectOutputStream)     */    private void readObject(ObjectInputStream s)      throws ClassNotFoundException, IOException, HeadlessException    {      GraphicsEnvironment.checkHeadless();      s.defaultReadObject();       Object keyOrNull;      while(null != (keyOrNull = s.readObject())) {        String key = ((String)keyOrNull).intern();         if (actionListenerK == key)          addActionListener((ActionListener)(s.readObject()));         else // skip value for unrecognized key          s.readObject();      }    }  /////////////////// Accessibility support

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