java.awt
Class MenuItem

java.lang.Object
  java.awt.MenuComponent
      java.awt.MenuItem

All Implemented Interfaces:

javax.accessibility.Accessible, Serializable

Direct Known Subclasses:

CheckboxMenuItem, Menu

public class MenuItem

extends MenuComponent

implements javax.accessibility.Accessible

All items in a menu must belong to the class MenuItem, or one of its subclasses.

The default MenuItem object embodies a simple labeled menu item.

This picture of a menu bar shows five menu items:
The first two items are simple menu items, labeled "Basic" and "Simple". Following these two items is a separator, which is itself a menu item, created with the label "-". Next is an instance of CheckboxMenuItem labeled "Check". The final menu item is a submenu labeled "More Examples", and this submenu is an instance of Menu.

When a menu item is selected, AWT sends an action event to the menu item. Since the event is an instance of ActionEvent, the processEvent method examines the event and passes it along to processActionEvent. The latter method redirects the event to any ActionListener objects that have registered an interest in action events generated by this menu item.

Note that the subclass Menu overrides this behavior and does not send any event to the frame until one of its subitems is selected.

Author:

Sami Shaio

See Also:

Serialized Form

Nested Class Summary

protected class

MenuItem.AccessibleAWTMenuItem Inner class of MenuItem used to provide default support for accessibility.

Nested classes inherited from class java.awt.MenuComponent

MenuComponent.AccessibleAWTMenuComponent

Field Summary

(package private) String	actionCommand This field indicates the command tha has been issued by a particular menu item.
(package private) ActionListener	actionListener
private static String	base
(package private) boolean	enabled A value to indicate whether a menu item is enabled or not.
(package private) long	eventMask The eventMask is ONLY set by subclasses via enableEvents.
(package private) String	label label is the label of a menu item.
private int	menuItemSerializedDataVersion Menu item serialized data version.
private static int	nameCounter
private static long	serialVersionUID
private MenuShortcut	shortcut A sequence of key stokes that ia associated with a menu item.

Fields inherited from class java.awt.MenuComponent

accessibleContext, actionListenerK, appContext, font, itemListenerK, newEventsOnly, parent, peer

Constructor Summary

MenuItem()
Constructs a new MenuItem with an empty label and no keyboard shortcut.

MenuItem(String label)
Constructs a new MenuItem with the specified label and no keyboard shortcut.

MenuItem(String label, MenuShortcut s)
Create a menu item with an associated keyboard shortcut.

Method Summary

void	addActionListener(ActionListener l) Adds the specified action listener to receive action events from this menu item.
void	addNotify() Creates the menu item's peer.
(package private) String	constructComponentName() Construct a name for this MenuComponent.
void	deleteShortcut() Delete any MenuShortcut object associated with this menu item.
(package private) void	deleteShortcut(MenuShortcut s)
void	disable() Deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).
protected void	disableEvents(long eventsToDisable) Disables event delivery to this menu item for events defined by the specified event mask parameter.
(package private) void	doMenuEvent(long when, int modifiers)
void	enable() Deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).
void	enable(boolean b) Deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).
protected void	enableEvents(long eventsToEnable) Enables event delivery to this menu item for events to be defined by the specified event mask parameter Since event types are automatically enabled when a listener for that type is added to the menu item, this method only needs to be invoked by subclasses of MenuItem which desire to have the specified event types delivered to processEvent regardless of whether a listener is registered.
(package private) boolean	eventEnabled(AWTEvent e)
javax.accessibility.AccessibleContext	getAccessibleContext() Gets the AccessibleContext associated with this MenuItem.
String	getActionCommand() Gets the command name of the action event that is fired by this menu item.
ActionListener[]	getActionListeners() Returns an array of all the action listeners registered on this menu item.
String	getLabel() Gets the label for this menu item.
EventListener[]	getListeners(Class listenerType) Returns an array of all the objects currently registered as FooListeners upon this MenuItem.
MenuShortcut	getShortcut() Get the MenuShortcut object associated with this menu item,
(package private) MenuItem	getShortcutMenuItem(MenuShortcut s)
(package private) boolean	handleShortcut(KeyEvent e)
private static void	initIDs() Initialize JNI field and method IDs
boolean	isEnabled() Checks whether this menu item is enabled.
String	paramString() Returns a string representing the state of this MenuItem.
protected void	processActionEvent(ActionEvent e) Processes action events occurring on this menu item, by dispatching them to any registered ActionListener objects.
protected void	processEvent(AWTEvent e) Processes events on this menu item.
private void	readObject(ObjectInputStream s) Reads the ObjectInputStream and if it isn't null adds a listener to receive action events fired by the Menu Item.
void	removeActionListener(ActionListener l) Removes the specified action listener so it no longer receives action events from this menu item.
void	setActionCommand(String command) Sets the command name of the action event that is fired by this menu item.
void	setEnabled(boolean b) Sets whether or not this menu item can be chosen.
void	setLabel(String label) Sets the label for this menu item to the specified label.
void	setShortcut(MenuShortcut s) Set the MenuShortcut object associated with this menu item.
private void	writeObject(ObjectOutputStream s) Writes default serializable fields to stream.

Methods inherited from class java.awt.MenuComponent

dispatchEvent, dispatchEventImpl, getAccessibleIndexInParent, getAccessibleStateSet, getFont_NoClientCode, getFont, getName, getParent_NoClientCode, getParent, getPeer, getTreeLock, postEvent, removeNotify, setFont, setName, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

enabled

boolean enabled

A value to indicate whether a menu item is enabled or not. If it is enabled, enabled will be set to true. Else enabled will be set to false.

See Also:

isEnabled(), setEnabled(boolean)

label

String label

label is the label of a menu item. It can be any string.

See Also:

getLabel(), setLabel(String)

actionCommand

String actionCommand

This field indicates the command tha has been issued by a particular menu item. By default the actionCommand is the label of the menu item, unless it has been set using setActionCommand.

See Also:

setActionCommand(String), getActionCommand()

eventMask

long eventMask

The eventMask is ONLY set by subclasses via enableEvents. The mask should NOT be set when listeners are registered so that we can distinguish the difference between when listeners request events and subclasses request them.

actionListener

transient ActionListener actionListener

shortcut

private MenuShortcut shortcut

A sequence of key stokes that ia associated with a menu item. Note :in 1.1.2 you must use setActionCommand() on a menu item in order for its shortcut to work.

See Also:

getShortcut(), setShortcut(MenuShortcut), deleteShortcut()

base

private static final String base

See Also:

Constant Field Values

nameCounter

private static int nameCounter

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

menuItemSerializedDataVersion

private int menuItemSerializedDataVersion

Menu item serialized data version.

Constructor Detail

MenuItem

public MenuItem()
         throws HeadlessException

Constructs a new MenuItem with an empty label and no keyboard shortcut.

Throws:

HeadlessException - if GraphicsEnvironment.isHeadless() returns true.

Since:

JDK1.1

See Also:

GraphicsEnvironment.isHeadless()

MenuItem

public MenuItem(String label)
         throws HeadlessException

Constructs a new MenuItem with the specified label and no keyboard shortcut. Note that use of "-" in a label is reserved to indicate a separator between menu items. By default, all menu items except for separators are enabled.

Parameters:

label - the label for this menu item.

Throws:

HeadlessException - if GraphicsEnvironment.isHeadless() returns true.

Since:

JDK1.0

See Also:

GraphicsEnvironment.isHeadless()

MenuItem

public MenuItem(String label,
                MenuShortcut s)
         throws HeadlessException

Create a menu item with an associated keyboard shortcut. Note that use of "-" in a label is reserved to indicate a separator between menu items. By default, all menu items except for separators are enabled.

Parameters:

label - the label for this menu item.

s - the instance of MenuShortcut associated with this menu item.

Throws:

HeadlessException - if GraphicsEnvironment.isHeadless() returns true.

Since:

JDK1.1

See Also:

GraphicsEnvironment.isHeadless()

Method Detail

constructComponentName

String constructComponentName()

Construct a name for this MenuComponent. Called by getName() when the name is null.

Overrides:

constructComponentName in class MenuComponent

Returns:

a name for this MenuComponent

addNotify

public void addNotify()

Creates the menu item's peer. The peer allows us to modify the appearance of the menu item without changing its functionality.

getLabel

public String getLabel()

Gets the label for this menu item.

Returns:

the label of this menu item, or null if this menu item has no label.

Since:

JDK1.0

See Also:

setLabel(java.lang.String)

setLabel

public void setLabel(String label)

Sets the label for this menu item to the specified label.

Parameters:

label - the new label, or null for no label.

Since:

JDK1.0

See Also:

getLabel()

isEnabled

public boolean isEnabled()

Checks whether this menu item is enabled.

Since:

JDK1.0

See Also:

setEnabled(boolean)

setEnabled

public void setEnabled(boolean b)

Sets whether or not this menu item can be chosen.

Parameters:

b - if true, enables this menu item; if false, disables it.

Since:

JDK1.1

See Also:

isEnabled()

enable

public void enable()

Deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).

enable

public void enable(boolean b)

Deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).

disable

public void disable()

Deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).

getShortcut

public MenuShortcut getShortcut()

Get the MenuShortcut object associated with this menu item,

Returns:

the menu shortcut associated with this menu item, or null if none has been specified.

Since:

JDK1.1

See Also:

setShortcut(java.awt.MenuShortcut)

setShortcut

public void setShortcut(MenuShortcut s)

Set the MenuShortcut object associated with this menu item. If a menu shortcut is already associated with this menu item, it is replaced.

Parameters:

s - the menu shortcut to associate with this menu item.

Since:

JDK1.1

See Also:

getShortcut()

deleteShortcut

public void deleteShortcut()

Delete any MenuShortcut object associated with this menu item.

Since:

JDK1.1

deleteShortcut

void deleteShortcut(MenuShortcut s)

doMenuEvent

void doMenuEvent(long when,
                 int modifiers)

handleShortcut

boolean handleShortcut(KeyEvent e)

getShortcutMenuItem

MenuItem getShortcutMenuItem(MenuShortcut s)

enableEvents

protected final void enableEvents(long eventsToEnable)

Enables event delivery to this menu item for events to be defined by the specified event mask parameter

Since event types are automatically enabled when a listener for that type is added to the menu item, this method only needs to be invoked by subclasses of MenuItem which desire to have the specified event types delivered to processEvent regardless of whether a listener is registered.

Parameters:

eventsToEnable - the event mask defining the event types

Since:

JDK1.1

See Also:

processEvent(java.awt.AWTEvent), disableEvents(long), Component.enableEvents(long)

disableEvents

protected final void disableEvents(long eventsToDisable)

Disables event delivery to this menu item for events defined by the specified event mask parameter.

Parameters:

eventsToDisable - the event mask defining the event types

Since:

JDK1.1

See Also:

processEvent(java.awt.AWTEvent), enableEvents(long), Component.disableEvents(long)

setActionCommand

public void setActionCommand(String command)

Sets the command name of the action event that is fired by this menu item.

By default, the action command is set to the label of the menu item.

Parameters:

command - the action command to be set for this menu item.

Since:

JDK1.1

See Also:

getActionCommand()

getActionCommand

public String getActionCommand()

Gets the command name of the action event that is fired by this menu item.

Since:

JDK1.1

See Also:

setActionCommand(java.lang.String)

addActionListener

public void addActionListener(ActionListener l)

Adds the specified action listener to receive action events from this menu item. If l is null, no exception is thrown and no action is performed.

Parameters:

l - the action listener.

Since:

JDK1.1

See Also:

removeActionListener(java.awt.event.ActionListener), getActionListeners(), ActionEvent, ActionListener

removeActionListener

public void removeActionListener(ActionListener l)

Removes the specified action listener so it no longer receives action events from this menu item. If l is null, no exception is thrown and no action is performed.

Parameters:

l - the action listener.

Since:

JDK1.1

See Also:

addActionListener(java.awt.event.ActionListener), getActionListeners(), ActionEvent, ActionListener

getActionListeners

public ActionListener[] getActionListeners()

Returns an array of all the action listeners registered on this menu item.

Returns:

all of this menu item's ActionListeners or an empty array if no action listeners are currently registered

Since:

1.4

See Also:

addActionListener(java.awt.event.ActionListener), removeActionListener(java.awt.event.ActionListener), ActionEvent, ActionListener

getListeners

public EventListener[] getListeners(Class listenerType)

Returns an array of all the objects currently registered as FooListeners upon this MenuItem. 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 MenuItem m for its action listeners with the following code:

ActionListener[] als = (ActionListener[])(m.getListeners(ActionListener.class));

If no such listeners exist, this method returns an empty array.

Parameters:

listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener

Returns:

an array of all objects registered as FooListeners on this menu item, or an empty array if no such listeners have been added

Throws:

ClassCastException - if listenerType doesn't specify a class or interface that implements java.util.EventListener

Since:

1.3

See Also:

getActionListeners()

processEvent

protected void processEvent(AWTEvent e)

Processes events on this menu item. If the event is an instance of ActionEvent, it invokes processActionEvent, another method defined by MenuItem.

Currently, menu items only support action events.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

Overrides:

processEvent in class MenuComponent

Parameters:

e - the event

Since:

JDK1.1

See Also:

processActionEvent(java.awt.event.ActionEvent)

eventEnabled

boolean eventEnabled(AWTEvent e)

Overrides:

eventEnabled in class MenuComponent

processActionEvent

protected void processActionEvent(ActionEvent e)

Processes action events occurring on this menu item, by dispatching them to any registered ActionListener objects. This method is not called unless action events are enabled for this component. Action events are enabled when one of the following occurs:

• An ActionListener object is registered via addActionListener.
• Action events are enabled via enableEvents.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

Parameters:

e - the action event

Since:

JDK1.1

See Also:

ActionEvent, ActionListener, enableEvents(long)

paramString

public String paramString()

Returns a string representing the state of this MenuItem. 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.

Overrides:

paramString in class MenuComponent

Returns:

the parameter string of this menu item

writeObject

private void writeObject(ObjectOutputStream s)
                  throws IOException

Writes default serializable fields to stream. Writes a list of serializable ActionListeners as optional data. The non-serializable listeners are detected and no attempt is made to serialize them.

Parameters:

s - the ObjectOutputStream to write

Throws:

IOException

See Also:

AWTEventMulticaster.save(ObjectOutputStream, String, EventListener), readObject(ObjectInputStream)

readObject

private void readObject(ObjectInputStream s)
                 throws ClassNotFoundException,
                        IOException,
                        HeadlessException

Reads the ObjectInputStream and if it isn't null adds a listener to receive action events fired by the Menu Item. Unrecognized keys or values will be ignored.

Parameters:

s - the ObjectInputStream to read

Throws:

HeadlessException - if GraphicsEnvironment.isHeadless returns true

ClassNotFoundException

IOException

See Also:

#removeActionListener(actionListener), #addActionListener(actionListener), writeObject(ObjectOutputStream)

initIDs

private static void initIDs()

Initialize JNI field and method IDs

getAccessibleContext

public javax.accessibility.AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this MenuItem. For menu items, the AccessibleContext takes the form of an AccessibleAWTMenuItem. A new AccessibleAWTMenuItem instance is created if necessary.

Specified by:

getAccessibleContext in interface javax.accessibility.Accessible

Overrides:

getAccessibleContext in class MenuComponent

Returns:

an AccessibleAWTMenuItem that serves as the AccessibleContext of this MenuItem