Class java.awt.MenuItem - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.awt.MenuItem

java.lang.Object
   |
   +----java.awt.MenuComponent
           |
           +----java.awt.MenuItem

public class MenuItem
extends MenuComponent

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.

MenuItem(): Constructs a new MenuItem with an empty label and no keyboard shortcut.
MenuItem(String): Constructs a new MenuItem with the specified label and no keyboard shortcut.
MenuItem(String, MenuShortcut): Create a menu item with an associated keyboard shortcut.

addActionListener(ActionListener): Adds the specified action listener to receive action events from this menu item.
addNotify(): Creates the menu item's peer.
deleteShortcut(): Delete any MenuShortcut object associated with this menu item.
disable(): Deprecated.
disableEvents(long): Disables event delivery to this menu item for events defined by the specified event mask parameter.
enable(): Deprecated.
enable(boolean): Deprecated.
enableEvents(long): 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.
getActionCommand(): Gets the command name of the action event that is fired by this menu item.
getLabel(): Gets the label for this menu item.
getShortcut(): Get the MenuShortcut object associated with this menu item,
isEnabled(): Checks whether this menu item is enabled.
paramString(): Returns the parameter string representing the state of this menu item.
processActionEvent(ActionEvent): Processes action events occurring on this menu item, by dispatching them to any registered ActionListener objects.
processEvent(AWTEvent): Processes events on this menu item.
removeActionListener(ActionListener): Removes the specified action listener so it no longer receives action events from this menu item.
setActionCommand(String): Sets the command name of the action event that is fired by this menu item.
setEnabled(boolean): Sets whether or not this menu item can be chosen.
setLabel(String): Sets the label for this menu item to the specified label.
setShortcut(MenuShortcut): Set the MenuShortcut object associated with this menu item.

MenuItem

 public MenuItem()

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

MenuItem

 public MenuItem(String label)

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.

MenuItem

 public MenuItem(String label,
                 MenuShortcut s)

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.

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.
See Also:: setLabel

setLabel

 public synchronized 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.
See Also:: getLabel

isEnabled

 public boolean isEnabled()

Checks whether this menu item is enabled.

See Also:: setEnabled

setEnabled

 public synchronized 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.
See Also:: isEnabled

enable

 public synchronized void enable()

Note: enable() is deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).

enable

 public void enable(boolean b)

Note: enable() is deprecated. As of JDK version 1.1, replaced by setEnabled(boolean).

disable

 public synchronized void disable()

Note: disable() is 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.
See Also:: setShortcut

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.
See Also:: getShortcut

deleteShortcut

 public void deleteShortcut()

Delete any MenuShortcut object associated with this menu item.

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.
See Also:: processEvent, disableEvents, enableEvents

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.
See Also:: processEvent, enableEvents, disableEvents

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.
See Also:: getActionCommand

getActionCommand

 public String getActionCommand()

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

See Also:: setActionCommand

addActionListener

 public synchronized void addActionListener(ActionListener l)

Adds the specified action listener to receive action events from this menu item.

Parameters:: l - the action listener.
See Also:: ActionEvent, ActionListener, removeActionListener

removeActionListener

 public synchronized void removeActionListener(ActionListener l)

Removes the specified action listener so it no longer receives action events from this menu item.

Parameters:: l - the action listener.
See Also:: ActionEvent, ActionListener, addActionListener

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.

Parameters:: e - the event.
Overrides:: processEvent in class MenuComponent
See Also:: processActionEvent

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.

Parameters:: e - the action event.
See Also:: ActionEvent, ActionListener, enableEvents

paramString

 public String paramString()

Returns the parameter string representing the state of this menu item. This string is useful for debugging.

Returns:: the parameter string of this menu item.
Overrides:: paramString in class MenuComponent

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