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Choice.javaAPI DocJava SE 5 API25714Fri Aug 26 14:56:44 BST 2005java.awt

Choice

public class Choice extends Component implements ItemSelectable, Accessible
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:

The following text describes the graphic

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.

Some native platforms do not support arbitrary resizing of Choice components and the behavior of setSize()/getSize() is bound by such limitations. Native GUI Choice components' size are often bound by such attributes as font size and length of items contained within the Choice.

version
1.89 05/18/04
author
Sami Shaio
author
Arthur van Hoff
since
JDK1.0

Fields Summary
Vector
pItems
The items for the Choice. This can be a null value.
int
selectedIndex
The index of the current choice for this Choice or -1 if nothing is selected.
transient ItemListener
itemListener
private static final String
base
private static int
nameCounter
private static final long
serialVersionUID
private int
choiceSerializedDataVersion
Constructors Summary
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.

exception
HeadlessException if GraphicsEnvironment.isHeadless() returns true
see
java.awt.GraphicsEnvironment#isHeadless
see
#select(int)
see
#select(java.lang.String)


                                                                                   
        
        GraphicsEnvironment.checkHeadless();
	pItems = new Vector();
    
Methods Summary
public voidadd(java.lang.String item)
Adds an item to this Choice menu.

param
item the item to be added
exception
NullPointerException if the item's value is null
since
JDK1.1

	addItem(item);
    
public voidaddItem(java.lang.String item)
Obsolete as of Java 2 platform v1.1. Please use the add method instead.

Adds an item to this Choice menu.

param
item the item to be added
exception
NullPointerException if the item's value is equal to null

        synchronized (this) {
	    insertNoInvalidate(item, pItems.size());
	}

	// This could change the preferred size of the Component.
	if (valid) {
	    invalidate();
	}
    
public synchronized voidaddItemListener(java.awt.event.ItemListener l)
Adds the specified item listener to receive item events from this Choice menu. Item events are sent in response to user input, but not in response to calls to select. If l is null, no exception is thrown and no action is performed.

param
l the item listener
see
#removeItemListener
see
#getItemListeners
see
#select
see
java.awt.event.ItemEvent
see
java.awt.event.ItemListener
since
JDK1.1

	if (l == null) {
	   return;
	}
        itemListener = AWTEventMulticaster.add(itemListener, l);
        newEventsOnly = true;
    
public voidaddNotify()
Creates the Choice's peer. This peer allows us to change the look of the Choice without changing its functionality.

see
java.awt.Toolkit#createChoice(java.awt.Choice)
see
java.awt.Component#getToolkit()

        synchronized (getTreeLock()) {
	    if (peer == null)
	        peer = getToolkit().createChoice(this);
	    super.addNotify();
	}
    
java.lang.StringconstructComponentName()
Constructs a name for this component. Called by getName when the name is null.

        synchronized (getClass()) {
	    return base + nameCounter++;
	}
    
public intcountItems()

deprecated
As of JDK version 1.1, replaced by getItemCount().

	return pItems.size();
    
booleaneventEnabled(java.awt.AWTEvent e)

        if (e.id == ItemEvent.ITEM_STATE_CHANGED) {
            if ((eventMask & AWTEvent.ITEM_EVENT_MASK) != 0 ||
                itemListener != null) {
                return true;
            }
            return false;
        }
        return super.eventEnabled(e);
    
public javax.accessibility.AccessibleContextgetAccessibleContext()
Gets the AccessibleContext associated with this Choice. For Choice components, the AccessibleContext takes the form of an AccessibleAWTChoice. A new AccessibleAWTChoice instance is created if necessary.

return
an AccessibleAWTChoice that serves as the AccessibleContext of this Choice

        if (accessibleContext == null) {
            accessibleContext = new AccessibleAWTChoice();
        }
        return accessibleContext;
    
public java.lang.StringgetItem(int index)
Gets the string at the specified index in this Choice menu.

param
index the index at which to begin
see
#getItemCount

	return getItemImpl(index);
    
public intgetItemCount()
Returns the number of items in this Choice menu.

return
the number of items in this Choice menu
see
#getItem
since
JDK1.1

	return countItems();
    
final java.lang.StringgetItemImpl(int index)

	return (String)pItems.elementAt(index);
    
public synchronized java.awt.event.ItemListener[]getItemListeners()
Returns an array of all the item listeners registered on this choice.

return
all of this choice's ItemListeners or an empty array if no item listeners are currently registered
see
#addItemListener
see
#removeItemListener
see
java.awt.event.ItemEvent
see
java.awt.event.ItemListener
since
1.4

        return (ItemListener[])(getListeners(ItemListener.class));
    
public T[]getListeners(java.lang.Class listenerType)
Returns an array of all the objects currently registered as FooListeners upon this Choice. 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 Choice c for its item listeners with the following code:

ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.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 choice, 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
#getItemListeners
since
1.3

	EventListener l = null;
	if  (listenerType == ItemListener.class) { 
	    l = itemListener;
	} else {
	    return super.getListeners(listenerType);
	}
	return AWTEventMulticaster.getListeners(l, listenerType);
    
public intgetSelectedIndex()
Returns the index of the currently selected item. If nothing is selected, returns -1.

return
the index of the currently selected item, or -1 if nothing is currently selected
see
#getSelectedItem

	return selectedIndex;
    
public synchronized java.lang.StringgetSelectedItem()
Gets a representation of the current choice as a string.

return
a string representation of the currently selected item in this choice menu
see
#getSelectedIndex

	return (selectedIndex >= 0) ? getItem(selectedIndex) : null;
    
public synchronized java.lang.Object[]getSelectedObjects()
Returns an array (length 1) containing the currently selected item. If this choice has no items, returns null.

see
ItemSelectable

	if (selectedIndex >= 0) {
            Object[] items = new Object[1];
            items[0] = getItem(selectedIndex);
            return items;
        }
        return null;
    
public voidinsert(java.lang.String item, int index)
Inserts the item into this choice at the specified position. Existing items at an index greater than or equal to index are shifted up by one to accommodate the new item. If index is greater than or equal to the number of items in this choice, item is added to the end of this choice.

If the item is the first one being added to the choice, then the item becomes selected. Otherwise, if the selected item was one of the items shifted, the first item in the choice becomes the selected item. If the selected item was no among those shifted, it remains the selected item.

param
item the non-null item to be inserted
param
index the position at which the item should be inserted
exception
IllegalArgumentException if index is less than 0

        synchronized (this) {
	    if (index < 0) {
	        throw new IllegalArgumentException("index less than zero.");
	    }
            /* if the index greater than item count, add item to the end */            
            index = Math.min(index, pItems.size());

            insertNoInvalidate(item, index);
	}

	// This could change the preferred size of the Component.
	if (valid) {
	    invalidate();
	}
    
private voidinsertNoInvalidate(java.lang.String item, int index)
Inserts an item to this Choice, but does not invalidate the Choice. Client methods must provide their own synchronization before invoking this method.

param
item the item to be added
param
index the new item position
exception
NullPointerException if the item's value is equal to null

        if (item == null) {
	    throw new 
	        NullPointerException("cannot add null item to Choice");
	}
	pItems.insertElementAt(item, index);
	ChoicePeer peer = (ChoicePeer)this.peer;
	if (peer != null) {
	    peer.addItem(item, index);
	}
	// no selection or selection shifted up
	if (selectedIndex < 0 || selectedIndex >= index) {
	    select(0);
	}
    
protected java.lang.StringparamString()
Returns a string representing the state of this Choice menu. 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 Choice menu

	return super.paramString() + ",current=" + getSelectedItem();
    
protected voidprocessEvent(java.awt.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.

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.ItemEvent
see
#processItemEvent
since
JDK1.1

        if (e instanceof ItemEvent) {
            processItemEvent((ItemEvent)e);
            return;
        }
	super.processEvent(e);
    
protected voidprocessItemEvent(java.awt.event.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.

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

param
e the item event
see
java.awt.event.ItemEvent
see
java.awt.event.ItemListener
see
#addItemListener(ItemListener)
see
java.awt.Component#enableEvents
since
JDK1.1

        ItemListener listener = itemListener;
        if (listener != null) {
            listener.itemStateChanged(e);
        }
    
private voidreadObject(java.io.ObjectInputStream s)
Reads the ObjectInputStream and if it isn't null adds a listener to receive item events fired by the Choice item. Unrecognized keys or values will be ignored.

param
s the ObjectInputStream to read
exception
HeadlessException if GraphicsEnvironment.isHeadless returns true
serial
see
#removeItemListener(ItemListener)
see
#addItemListener(ItemListener)
see
java.awt.GraphicsEnvironment#isHeadless
see
#writeObject(ObjectOutputStream)

      GraphicsEnvironment.checkHeadless();
      s.defaultReadObject();

      Object keyOrNull;
      while(null != (keyOrNull = s.readObject())) {
	String key = ((String)keyOrNull).intern();

	if (itemListenerK == key)
	  addItemListener((ItemListener)(s.readObject()));

	else // skip value for unrecognized key
	  s.readObject();
      }
    
public voidremove(java.lang.String item)
Removes the first occurrence of item from the Choice menu. If the item being removed is the currently selected item, then the first item in the choice becomes the selected item. Otherwise, the currently selected item remains selected (and the selected index is updated accordingly).

param
item the item to remove from this Choice menu
exception
IllegalArgumentException if the item doesn't exist in the choice menu
since
JDK1.1

        synchronized (this) {
	    int index = pItems.indexOf(item);
	    if (index < 0) {
	        throw new IllegalArgumentException("item " + item +
						   " not found in choice");
	    } else {
	        removeNoInvalidate(index);
	    }
	}

	// This could change the preferred size of the Component.
	if (valid) {
	    invalidate();
	}
    
public voidremove(int position)
Removes an item from the choice menu at the specified position. If the item being removed is the currently selected item, then the first item in the choice becomes the selected item. Otherwise, the currently selected item remains selected (and the selected index is

param
position the position of the item
throws
IndexOutOfBoundsException if the specified position is out of bounds
since
JDK1.1

        synchronized (this) {
	    removeNoInvalidate(position);
	}

	// This could change the preferred size of the Component.
	if (valid) {
	    invalidate();
	}
    
public voidremoveAll()
Removes all items from the choice menu.

see
#remove
since
JDK1.1

        synchronized (this) {
            if (peer != null) {
                ((ChoicePeer)peer).removeAll();
            }
            pItems.removeAllElements();
            selectedIndex = -1;
	}

	// This could change the preferred size of the Component.
	if (valid) {
	    invalidate();
	}
    
public synchronized voidremoveItemListener(java.awt.event.ItemListener l)
Removes the specified item listener so that it no longer receives item events from this Choice menu. If l is null, no exception is thrown and no action is performed.

param
l the item listener
see
#addItemListener
see
#getItemListeners
see
java.awt.event.ItemEvent
see
java.awt.event.ItemListener
since
JDK1.1

	if (l == null) {
	    return;
	}
        itemListener = AWTEventMulticaster.remove(itemListener, l);
    
private voidremoveNoInvalidate(int position)
Removes an item from the Choice at the specified position, but does not invalidate the Choice. Client methods must provide their own synchronization before invoking this method.

param
position the position of the item

        pItems.removeElementAt(position);
	ChoicePeer peer = (ChoicePeer)this.peer;
	if (peer != null) {
	    peer.remove(position);
	}
	/* Adjust selectedIndex if selected item was removed. */
	if (pItems.size() == 0) {
	    selectedIndex = -1;
	} else if (selectedIndex == position) {
	    select(0);
	} else if (selectedIndex > position) {
	    select(selectedIndex-1);
	}
    
public synchronized voidselect(int pos)
Sets the selected item in this Choice menu to be the item at the specified position.

Note that this method should be primarily used to initially select an item in this component. Programmatically calling this method will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

param
pos the positon of the selected item
exception
IllegalArgumentException if the specified position is greater than the number of items or less than zero
see
#getSelectedItem
see
#getSelectedIndex

	if ((pos >= pItems.size()) || (pos < 0)) {
	    throw new IllegalArgumentException("illegal Choice item position: " + pos);
	}
	if (pItems.size() > 0) {
	    selectedIndex = pos;
	    ChoicePeer peer = (ChoicePeer)this.peer;
	    if (peer != null) {
		peer.select(pos);
	    }
	}
    
public synchronized voidselect(java.lang.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.

Note that this method should be primarily used to initially select an item in this component. Programmatically calling this method will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

param
str the specified string
see
#getSelectedItem
see
#getSelectedIndex

	int index = pItems.indexOf(str);
	if (index >= 0) {
	    select(index);
	}
    
private voidwriteObject(java.io.ObjectOutputStream s)
Writes default serializable fields to stream. Writes a list of serializable ItemListeners as optional data. The non-serializable ItemListeners are detected and no attempt is made to serialize them.

param
s the ObjectOutputStream to write
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: itemListenerK indicating an ItemListener object
see
AWTEventMulticaster#save(ObjectOutputStream, String, EventListener)
see
java.awt.Component#itemListenerK
see
#readObject(ObjectInputStream)


                                                                                                       
       
       
    
      s.defaultWriteObject();

      AWTEventMulticaster.save(s, itemListenerK, itemListener);
      s.writeObject(null);