* 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.
*
* 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.
*
* @author Sami Shaio
* @author Arthur van Hoff
* @since JDK1.0
*/
public class Choice extends Component implements ItemSelectable, Accessible {
/**
* The items for the Choice.
* This can be a null value.
* @serial
* @see #add(String)
* @see #addItem(String)
* @see #getItem(int)
* @see #getItemCount()
* @see #insert(String, int)
* @see #remove(String)
*/
Vector pItems;
/**
* The index of the current choice for this Choice
* or -1 if nothing is selected.
* @serial
* @see #getSelectedItem()
* @see #select(int)
*/
int selectedIndex = -1;
transient ItemListener itemListener;
private static final String base = "choice";
private static int nameCounter = 0;
/*
* JDK 1.1 serialVersionUID
*/
private static final long serialVersionUID = -4075310674757313071L;
/**
* 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)
*/
public Choice() throws HeadlessException {
GraphicsEnvironment.checkHeadless();
pItems = new Vector();
}
/**
* Constructs a name for this component. Called by
* getName when the name is null.
*/
String constructComponentName() {
synchronized (Choice.class) {
return base + nameCounter++;
}
}
/**
* 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()
*/
public void addNotify() {
synchronized (getTreeLock()) {
if (peer == null)
peer = getToolkit().createChoice(this);
super.addNotify();
}
}
/**
* Returns the number of items in this Choice menu.
* @return the number of items in this Choice menu
* @see #getItem
* @since JDK1.1
*/
public int getItemCount() {
return countItems();
}
/**
* @deprecated As of JDK version 1.1,
* replaced by getItemCount().
*/
@Deprecated
public int countItems() {
return pItems.size();
}
/**
* Gets the string at the specified index in this
* Choice menu.
* @param index the index at which to begin
* @see #getItemCount
*/
public String getItem(int index) {
return getItemImpl(index);
}
/*
* This is called by the native code, so client code can't
* be called on the toolkit thread.
*/
final String getItemImpl(int index) {
return (String)pItems.elementAt(index);
}
/**
* 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
*/
public void add(String item) {
addItem(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
*/
public void addItem(String item) {
synchronized (this) {
insertNoInvalidate(item, pItems.size());
}
// This could change the preferred size of the Component.
invalidateIfValid();
}
/**
* 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
*/
private void insertNoInvalidate(String item, int index) {
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.add(item, index);
}
// no selection or selection shifted up
if (selectedIndex < 0 || selectedIndex >= index) {
select(0);
}
}
/**
* 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
*/
public void insert(String item, int index) {
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.
invalidateIfValid();
}
/**
* 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
*/
public void remove(String item) {
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.
invalidateIfValid();
}
/**
* 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
* updated accordingly).
* @param position the position of the item
* @throws IndexOutOfBoundsException if the specified
* position is out of bounds
* @since JDK1.1
*/
public void remove(int position) {
synchronized (this) {
removeNoInvalidate(position);
}
// This could change the preferred size of the Component.
invalidateIfValid();
}
/**
* 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
*/
private void removeNoInvalidate(int position) {
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);
}
}
/**
* Removes all items from the choice menu.
* @see #remove
* @since JDK1.1
*/
public void removeAll() {
synchronized (this) {
if (peer != null) {
((ChoicePeer)peer).removeAll();
}
pItems.removeAllElements();
selectedIndex = -1;
}
// This could change the preferred size of the Component.
invalidateIfValid();
}
/**
* 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
*/
public synchronized String getSelectedItem() {
return (selectedIndex >= 0) ? getItem(selectedIndex) : null;
}
/**
* Returns an array (length 1) containing the currently selected
* item. If this choice has no items, returns null.
* @see ItemSelectable
*/
public synchronized Object[] getSelectedObjects() {
if (selectedIndex >= 0) {
Object[] items = new Object[1];
items[0] = getItem(selectedIndex);
return items;
}
return null;
}
/**
* 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
*/
public int getSelectedIndex() {
return selectedIndex;
}
/**
* 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
*/
public synchronized void select(int pos) {
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);
}
}
}
/**
* 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
*/
public synchronized void select(String str) {
int index = pItems.indexOf(str);
if (index >= 0) {
select(index);
}
}
/**
* 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.
*
Refer to AWT Threading Issues for details on AWT's threading model.
* @param l the item listener
* @see #removeItemListener
* @see #getItemListeners
* @see #select
* @see java.awt.event.ItemEvent
* @see java.awt.event.ItemListener
* @since JDK1.1
*/
public synchronized void addItemListener(ItemListener l) {
if (l == null) {
return;
}
itemListener = AWTEventMulticaster.add(itemListener, l);
newEventsOnly = true;
}
/**
* 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.
*
Refer to AWT Threading Issues for details on AWT's threading model.
* @param l the item listener
* @see #addItemListener
* @see #getItemListeners
* @see java.awt.event.ItemEvent
* @see java.awt.event.ItemListener
* @since JDK1.1
*/
public synchronized void removeItemListener(ItemListener l) {
if (l == null) {
return;
}
itemListener = AWTEventMulticaster.remove(itemListener, l);
}
/**
* 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
*/
public synchronized ItemListener[] getItemListeners() {
return (ItemListener[])(getListeners(ItemListener.class));
}
/**
* 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
*/
public 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
*/
protected void processEvent(AWTEvent e) {
if (e instanceof ItemEvent) {
processItemEvent((ItemEvent)e);
return;
}
super.processEvent(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: *
ItemListener object is registered
* via addItemListener.
* 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
*/
protected void processItemEvent(ItemEvent e) {
ItemListener listener = itemListener;
if (listener != null) {
listener.itemStateChanged(e);
}
}
/**
* 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
*/
protected String paramString() {
return super.paramString() + ",current=" + getSelectedItem();
}
/* Serialization support.
*/
/*
* Choice Serial Data Version.
* @serial
*/
private int choiceSerializedDataVersion = 1;
/**
* 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)
*/
private void writeObject(ObjectOutputStream s)
throws java.io.IOException
{
s.defaultWriteObject();
AWTEventMulticaster.save(s, itemListenerK, itemListener);
s.writeObject(null);
}
/**
* 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)
*/
private void readObject(ObjectInputStream s)
throws ClassNotFoundException, IOException, HeadlessException
{
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();
}
}
/////////////////
// Accessibility support
////////////////
/**
* 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
* @since 1.3
*/
public AccessibleContext getAccessibleContext() {
if (accessibleContext == null) {
accessibleContext = new AccessibleAWTChoice();
}
return accessibleContext;
}
/**
* This class implements accessibility support for the
* Choice class. It provides an implementation of the
* Java Accessibility API appropriate to choice user-interface elements.
* @since 1.3
*/
protected class AccessibleAWTChoice extends AccessibleAWTComponent
implements AccessibleAction
{
/*
* JDK 1.3 serialVersionUID
*/
private static final long serialVersionUID = 7175603582428509322L;
public AccessibleAWTChoice() {
super();
}
/**
* Get the AccessibleAction associated with this object. In the
* implementation of the Java Accessibility API for this class,
* return this object, which is responsible for implementing the
* AccessibleAction interface on behalf of itself.
*
* @return this object
* @see AccessibleAction
*/
public AccessibleAction getAccessibleAction() {
return this;
}
/**
* Get the role of this object.
*
* @return an instance of AccessibleRole describing the role of the
* object
* @see AccessibleRole
*/
public AccessibleRole getAccessibleRole() {
return AccessibleRole.COMBO_BOX;
}
/**
* Returns the number of accessible actions available in this object
* If there are more than one, the first one is considered the "default"
* action of the object.
*
* @return the zero-based number of Actions in this object
*/
public int getAccessibleActionCount() {
return 0; // To be fully implemented in a future release
}
/**
* Returns a description of the specified action of the object.
*
* @param i zero-based index of the actions
* @return a String description of the action
* @see #getAccessibleActionCount
*/
public String getAccessibleActionDescription(int i) {
return null; // To be fully implemented in a future release
}
/**
* Perform the specified Action on the object
*
* @param i zero-based index of actions
* @return true if the action was performed; otherwise false.
* @see #getAccessibleActionCount
*/
public boolean doAccessibleAction(int i) {
return false; // To be fully implemented in a future release
}
} // inner class AccessibleAWTChoice
}