* Quit" button as it appears
* under the Solaris operating system:
*
*
*
* 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. *
* The gesture of clicking on a button with the mouse
* is associated with one instance of ActionEvent,
* 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 processMouseEvent,
* or it can register itself as a listener for mouse events by
* calling addMouseListener. Both of these methods are
* defined by Component, the abstract superclass of
* all components.
*
* When a button is pressed and released, AWT sends an instance
* of ActionEvent to the button, by calling
* processEvent on the button. The button's
* processEvent method receives all events
* for the button; it passes an action event along by
* calling its own processActionEvent 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.
*
* If an application wants to perform some action based on
* a button being pressed and released, it should implement
* ActionListener and register the new listener
* to receive events from this button, by calling the button's
* addActionListener 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 1.0
*/
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
* null 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 null
* 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 null
* 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 null then the action command
* is set to match the label of the button.
* @see java.awt.event.ActionEvent
* @since 1.1
*/
public void setActionCommand(String command) {
actionCommand = command;
}
/**
* Returns the command name of the action event fired by this button.
* If the command name is null (default) then this method
* returns the label of the button.
*
* @return the action command name (or label) for this 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.
*
Refer to AWT Threading Issues for details on AWT's threading model. * * @param l the action listener * @see #removeActionListener * @see #getActionListeners * @see java.awt.event.ActionListener * @since 1.1 */ 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. *
Refer to AWT Threading Issues for details on AWT's threading model.
*
* @param l the action listener
* @see #addActionListener
* @see #getActionListeners
* @see java.awt.event.ActionListener
* @since 1.1
*/
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 ActionListeners
* 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 getListeners(ActionListener.class);
}
/**
* Returns an array of all the objects currently registered
* as FooListeners
* upon this Button.
* FooListeners are registered using the
* addFooListener method.
*
*
* You can specify the listenerType argument
* with a class literal, such as
* FooListener.class.
* For example, you can query a
* Button b
* for its action listeners with the following code:
*
*
ActionListener[] als = (ActionListener[])(b.getListeners(ActionListener.class));* * 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 *
java.util.EventListener
* @return an array of all objects registered as
* FooListeners on this button,
* or an empty array if no such
* listeners have been added
* @exception ClassCastException if listenerType
* doesn't specify a class or interface that implements
* java.util.EventListener
*
* @see #getActionListeners
* @since 1.3
*/
public ActionEvent, this method invokes
* the processActionEvent method. Otherwise,
* it invokes processEvent on the superclass.
* Note that if the event parameter is null
* 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 1.1
*/
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
* ActionListener objects.
*
* This method is not called unless action events are * enabled for this button. Action events are enabled * when one of the following occurs: *
ActionListener object is registered
* via addActionListener.
* enableEvents.
* Note that if the event parameter is null
* 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 1.1
*/
protected void processActionEvent(ActionEvent e) {
ActionListener listener = actionListener;
if (listener != null) {
listener.actionPerformed(e);
}
}
/**
* Returns a string representing the state of this Button.
* 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
* null.
*
* @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 ActionListeners
* as optional data. The non-serializable
* ActionListeners are detected and
* no attempt is made to serialize them.
*
* @serialData null terminated sequence of 0 or
* more pairs: the pair consists of a String
* and an Object; the String
* indicates the type of object and is one of the following:
* actionListenerK indicating an
* ActionListener object
*
* @param s the ObjectOutputStream 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 ObjectInputStream and if
* it isn't null adds a listener to
* receive action events fired by the button.
* Unrecognized keys or values will be ignored.
*
* @param s the ObjectInputStream to read
* @exception HeadlessException if
* GraphicsEnvironment.isHeadless returns
* true
* @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
////////////////
/**
* Gets the AccessibleContext associated with
* this Button. For buttons, the
* AccessibleContext takes the form of an
* AccessibleAWTButton.
* A new AccessibleAWTButton instance is
* created if necessary.
*
* @return an AccessibleAWTButton that serves as the
* AccessibleContext of this Button
* @since 1.3
*/
@BeanProperty(expert = true, description
= "The AccessibleContext associated with this Button.")
public AccessibleContext getAccessibleContext() {
if (accessibleContext == null) {
accessibleContext = new AccessibleAWTButton();
}
return accessibleContext;
}
/**
* This class implements accessibility support for the
* Button class. It provides an implementation of the
* Java Accessibility API appropriate to button user-interface elements.
* @since 1.3
*/
protected class AccessibleAWTButton extends AccessibleAWTComponent
implements AccessibleAction, AccessibleValue
{
/*
* JDK 1.3 serialVersionUID
*/
private static final long serialVersionUID = -5932203980244017102L;
/**
* Get the accessible name of this object.
*
* @return the localized name of the object -- can be null if this
* object does not have a name
*/
public String getAccessibleName() {
if (accessibleName != null) {
return accessibleName;
} else {
if (getLabel() == null) {
return super.getAccessibleName();
} else {
return getLabel();
}
}
}
/**
* Get the AccessibleAction associated with this object. In the
* implementation of the Java Accessibility API for this class,
* return this object, which is responsible for implementing the
* AccessibleAction interface on behalf of itself.
*
* @return this object
*/
public AccessibleAction getAccessibleAction() {
return this;
}
/**
* Get the AccessibleValue associated with this object. In the
* implementation of the Java Accessibility API for this class,
* return this object, which is responsible for implementing the
* AccessibleValue interface on behalf of itself.
*
* @return this object
*/
public AccessibleValue getAccessibleValue() {
return this;
}
/**
* Returns the number of Actions available in this object. The
* default behavior of a button is to have one action - toggle
* the button.
*
* @return 1, the number of Actions in this object
*/
public int getAccessibleActionCount() {
return 1;
}
/**
* Return a description of the specified action of the object.
*
* @param i zero-based index of the actions
*/
public String getAccessibleActionDescription(int i) {
if (i == 0) {
// [[[PENDING: WDW -- need to provide a localized string]]]
return "click";
} else {
return null;
}
}
/**
* Perform the specified Action on the object
*
* @param i zero-based index of actions
* @return true if the the action was performed; else false.
*/
public boolean doAccessibleAction(int i) {
if (i == 0) {
// Simulate a button click
Toolkit.getEventQueue().postEvent(
new ActionEvent(Button.this,
ActionEvent.ACTION_PERFORMED,
Button.this.getActionCommand()));
return true;
} else {
return false;
}
}
/**
* Get the value of this object as a Number.
*
* @return An Integer of 0 if this isn't selected or an Integer of 1 if
* this is selected.
* @see javax.swing.AbstractButton#isSelected()
*/
public Number getCurrentAccessibleValue() {
return Integer.valueOf(0);
}
/**
* Set the value of this object as a Number.
*
* @return True if the value was set.
*/
public boolean setCurrentAccessibleValue(Number n) {
return false;
}
/**
* Get the minimum value of this object as a Number.
*
* @return An Integer of 0.
*/
public Number getMinimumAccessibleValue() {
return Integer.valueOf(0);
}
/**
* Get the maximum value of this object as a Number.
*
* @return An Integer of 0.
*/
public Number getMaximumAccessibleValue() {
return Integer.valueOf(0);
}
/**
* Get the role of this object.
*
* @return an instance of AccessibleRole describing the role of the
* object
* @see AccessibleRole
*/
public AccessibleRole getAccessibleRole() {
return AccessibleRole.PUSH_BUTTON;
}
} // inner class AccessibleAWTButton
}