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

All Packages  Class Hierarchy  This Package  Previous  Next  Index

Class java.awt.Choice

java.lang.Object
   |
   +----java.awt.Component
           |
           +----java.awt.Choice

public class Choice
extends Component
implements ItemSelectable

The Choice class presents a pop-up menu of choices. The current choice is displayed as the title of the menu.

The following code example produces a pop-up menu:

 Choice ColorChooser = new Choice();
 ColorChooser.add("Green");
 ColorChooser.add("Red");
 ColorChooser.add("Blue");

After this choice menu has been added to a panel, it appears as follows in its normal state:

In the picture, "Green" is the current choice. Pushing the mouse button down on the object causes a menu to appear with the current choice highlighted.

Choice(): Creates a new choice menu.

add(String): Adds an item to this Choice menu.
addItem(String): Adds an item to this Choice.
addItemListener(ItemListener): Adds the specified item listener to receive item events from this Choice menu.
addNotify(): Creates the Choice's peer.
countItems(): Deprecated.
getItem(int): Gets the string at the specified index in this Choice menu.
getItemCount(): Returns the number of items in this Choice menu.
getSelectedIndex(): Returns the index of the currently selected item.
getSelectedItem(): Gets a representation of the current choice as a string.
getSelectedObjects(): Returns an array (length 1) containing the currently selected item.
insert(String, int): Inserts the item into this choice at the specified position.
paramString(): Returns the parameter string representing the state of this choice menu.
processEvent(AWTEvent): Processes events on this choice.
processItemEvent(ItemEvent): Processes item events occurring on this Choice menu by dispatching them to any registered ItemListener objects.
remove(int): Removes an item from the choice menu at the specified position.
remove(String): Remove the first occurrence of item from the Choice menu.
removeAll(): Removes all items from the choice menu.
removeItemListener(ItemListener): Removes the specified item listener so that it no longer receives item events from this Choice menu.
select(int): Sets the selected item in this Choice menu to be the item at the specified position.
select(String): Sets the selected item in this Choice menu to be the item whose name is equal to the specified string.

Choice

 public Choice()

Creates a new choice menu. The menu initially has no items in it.

By default, the first item added to the choice menu becomes the selected item, until a different selection is made by the user by calling one of the select methods.

See Also:: select, select

addNotify

 public void addNotify()

Creates the Choice's peer. This peer allows us to change the look of the Choice without changing its functionality.

Overrides:: addNotify in class Component
See Also:: createChoice, getToolkit

getItemCount

 public int getItemCount()

Returns the number of items in this Choice menu.

See Also:: getItem

countItems

 public int countItems()

Note: countItems() is deprecated. As of JDK version 1.1, replaced by getItemCount().

getItem

 public String getItem(int index)

Gets the string at the specified index in this Choice menu.

Parameters:: index - the index at which to begin.
See Also:: getItemCount

add

 public void add(String item)

Adds an item to this Choice menu.

Parameters:: item - the item to be added
Throws: NullPointerException: if the item's value is null.

addItem

 public synchronized void addItem(String item)

Adds an item to this Choice.

Parameters:: item - the item to be added
Throws: NullPointerException: If the item's value is equal to null.

insert

 public synchronized void insert(String item,
                                 int index)

Inserts the item into this choice at the specified position.

Parameters:: item - the item to be inserted; index - the position at which the item should be inserted
Throws: IllegalArgumentException: if index is less than 0.

remove

 public synchronized void remove(String item)

Remove the first occurrence of item from the Choice menu.

Parameters:: item - the item to remove from this Choice menu.
Throws: IllegalArgumentException: if the item doesn't exist in the choice menu.

remove

 public synchronized void remove(int position)

Removes an item from the choice menu at the specified position.

Parameters:: position - the position of the item.

removeAll

 public synchronized void removeAll()

Removes all items from the choice menu.

See Also:: remove

getSelectedItem

 public synchronized String getSelectedItem()

Gets a representation of the current choice as a string.

Returns:: a string representation of the currently selected item in this choice menu.
See Also:: getSelectedIndex

getSelectedObjects

 public synchronized Object[] getSelectedObjects()

Returns an array (length 1) containing the currently selected item. If this choice has no items, returns null.

See Also:: ItemSelectable

getSelectedIndex

 public int getSelectedIndex()

Returns the index of the currently selected item.

See Also:: getSelectedItem

select

 public void select(int pos)

Sets the selected item in this Choice menu to be the item at the specified position.

Parameters:: pos - the positon of the selected item.
Throws: IllegalArgumentException: if the specified position is invalid.
See Also:: getSelectedItem, getSelectedIndex

select

 public synchronized void select(String str)

Sets the selected item in this Choice menu to be the item whose name is equal to the specified string. If more than one item matches (is equal to) the specified string, the one with the smallest index is selected.

Parameters:: str - the specified string
See Also:: getSelectedItem, getSelectedIndex

addItemListener

 public synchronized void addItemListener(ItemListener l)

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

Parameters:: l - the item listener.
See Also:: ItemEvent, ItemListener, removeItemListener

removeItemListener

 public synchronized void removeItemListener(ItemListener l)

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

Parameters:: l - the item listener.
See Also:: ItemEvent, ItemListener, addItemListener

processEvent

 protected void processEvent(AWTEvent e)

Processes events on this choice. If the event is an instance of ItemEvent, it invokes the processItemEvent method. Otherwise, it calls its superclass's processEvent method.

Parameters:: e - the event.
Overrides:: processEvent in class Component
See Also:: ItemEvent, processItemEvent

processItemEvent

 protected void processItemEvent(ItemEvent e)

Processes item events occurring on this Choice menu by dispatching them to any registered ItemListener objects.

This method is not called unless item events are enabled for this component. Item events are enabled when one of the following occurs:

An ItemListener object is registered via addItemListener.
Item events are enabled via enableEvents.

Parameters:: e - the item event.
See Also:: ItemEvent, ItemListener, addItemListener, enableEvents

paramString

 protected String paramString()

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

Returns:: the parameter string of this Choice menu.
Overrides:: paramString in class Component

All Packages  Class Hierarchy  This Package  Previous  Next  Index

Submit a bug or feature - Version 1.1.8 of Java Platform API Specification
Java is a trademark or registered trademark of Sun Microsystems, Inc. in the US and other countries.
Copyright 1995-1999 Sun Microsystems, Inc. 901 San Antonio Road,
Palo Alto, California, 94303, U.S.A. All Rights Reserved.