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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class MenuItem - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.awt
Class MenuItem

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

Direct Known Subclasses:

CheckboxMenuItem, Menu

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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.

See Also:

Serialized Form

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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.
void	deleteShortcut()           Delete any MenuShortcut object associated with this menu item.
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.
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
String	getActionCommand()           Gets the command name of the action event that is fired by this menu item.
String	getLabel()           Gets the label for this menu item.
MenuShortcut	getShortcut()           Get the MenuShortcut object associated with this menu item,
boolean	isEnabled()           Checks whether this menu item is enabled.
String	paramString()           Returns the parameter string representing the state of this menu item.
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.
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.

 

Methods inherited from class java.awt.MenuComponent

dispatchEvent, getFont, getName, 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

 

Constructor Detail

MenuItem

public MenuItem()

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

Since:

JDK1.1

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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.

Since:

JDK1.0

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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.

Since:

JDK1.1

Method Detail

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.

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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)

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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()

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isEnabled

public boolean isEnabled()

Checks whether this menu item is enabled.

Since:

JDK1.0

See Also:

setEnabled(boolean)

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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()

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enable

public void enable()

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

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enable

public void enable(boolean b)

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

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disable

public void disable()

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

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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)

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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()

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deleteShortcut

public void deleteShortcut()

Delete any MenuShortcut object associated with this menu item.

Since:

JDK1.1

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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)

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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)

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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()

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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)

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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:

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

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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:

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

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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.

Overrides:

processEvent in class MenuComponent

Parameters:

e - the event.

Since:

JDK1.1

See Also:

processActionEvent(java.awt.event.ActionEvent)

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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.

Since:

JDK1.1

See Also:

ActionEvent, ActionListener, enableEvents(long)

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paramString

public String paramString()

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

Overrides:

paramString in class MenuComponent

Returns:

the parameter string of this menu item.

Since:

JDK1.0

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