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Java Choice AWT Example

Java AWT Choice Examples

Usage:

The Choice class can be used to add a drop-down list of items to a container.

Package:

Java.awt

Subclass of:

Java.awt.Component

Common Constructors:

Choice (): Creates an empty Choice instance.

Common Methods:

void addItemListener (ItemListener Handler): Configures an event handler for the choice box.
void insert (String Item, int Index): Inserts the item into this choice at the specified position.
int getSelectedIndex (): Returns the index of the selected item.
void setBackground (Color BackgroundColor): Sets the background color of the choice box.
void setFont (Font TextFont): Sets the font for this component.
void setForeground (Color TextColor): Sets the color of the text for the choice box.
void Select (int Selection): Sets the index of the selected item.

Arguments:

BackgroundColor: The color to be used for the background of the choice box.
Index: Position where the item will be inserted.
Item: A String to be listed in the choice box.
Handler: The object which handles action events from this choice box.
Selection: The index of the selected item.
TextColor: The color to be used for the text of the choice box.
TextFont: The font to be used for the text of the choice box.

Example:

Code:

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class Choice2 extends Applet implements ItemListener {
  /* Declaration */
  private LayoutManager Layout;
  private Choice Selector;
  private Font SansSerif;

  public Choice2 () {
    /* Declaration */
    String [] ColorList;
    int i;
          
    /* Instantiation */
    ColorList = new String [9];
    SansSerif = new Font ("SansSerif", Font.BOLD, 14);
    Layout = new FlowLayout ();
    Selector = new Choice ();
    
    /* Decoration */
    ColorList [0] = "Red";
    ColorList [1] = "Magenta";
    ColorList [2] = "Blue";
    ColorList [3] = "Cyan";
    ColorList [4] = "Green";
    ColorList [5] = "Yellow";
    ColorList [6] = "White";
    ColorList [7] = "Gray";
    ColorList [8] = "Black";
    for (i = 0; i < ColorList.length; ++i) {
      Selector.insert (ColorList [i], i);
    }
    Selector.setBackground (Color.yellow);
    Selector.setForeground (Color.red);
    Selector.setFont (SansSerif);
            
    /* Location */
    setLayout (Layout);
    add (Selector);

    /* Configuration */
    Selector.addItemListener (this);

    /* Initialization */
    Selector.select (5);
    setBackground (Color.yellow);
  }

  public void itemStateChanged(ItemEvent e) {
    int Selection;
    Selection = Selector.getSelectedIndex();
    if (Selection == 0) {
      setBackground (Color.red);
    } else if (Selection == 1) {
      setBackground (Color.magenta);
    } else if (Selection == 2) {
      setBackground (Color.blue);
    } else if (Selection == 3) {
      setBackground (Color.cyan);
    } else if (Selection == 4) {
      setBackground (Color.green);
    } else if (Selection == 5) {
      setBackground (Color.yellow);
    } else if (Selection == 6) {
      setBackground (Color.white);
    } else if (Selection == 7) {
      setBackground (Color.gray);
    } else if (Selection == 8) {
      setBackground (Color.black);
    } 
  } 

}




____________________________

Class java.awt.Choice

java.lang.Object java.awt.Component java.awt.Choice

public class Choice
implements ItemSelectable, Accessible
extends Component

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.

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.

Inner Class Index
Class	Description
Choice.AccessibleAWTChoice	The class used to obtain the accessible role for this object.

Constructor Index
Constructor	Description
Choice()	Creates a new choice menu.

Method Index
Method	Description
void add(`String`)	Adds an item to this `Choice` menu.
void addItem(`String`)	Adds an item to this Choice.
void addItemListener(`ItemListener`)	Adds the specified item listener to receive item events from this `Choice` menu.
void addNotify()	Creates the Choice's peer.
int countItems()	Deprecated. As of JDK version 1.1, replaced by `getItemCount()`.
AccessibleContext getAccessibleContext()	Get the AccessibleContext associated with this Choice.
String getItem(`int`)	Gets the string at the specified index in this `Choice` menu.
int getItemCount()	Returns the number of items in this `Choice` menu.
EventListener[] getListeners(`Class`)	Return an array of all the listeners that were added to the Choice with addXXXListener(), where XXX is the name of the `listenerType` argument.
int getSelectedIndex()	Returns the index of the currently selected item.
String getSelectedItem()	Gets a representation of the current choice as a string.
Object[] getSelectedObjects()	Returns an array (length 1) containing the currently selected item.
void insert(`String`, `int`)	Inserts the item into this choice at the specified position.
String paramString()	Returns the parameter string representing the state of this choice menu.
void processEvent(`AWTEvent`)	Processes events on this choice.
void processItemEvent(`ItemEvent`)	Processes item events occurring on this `Choice` menu by dispatching them to any registered `ItemListener` objects.
void remove(`int`)	Removes an item from the choice menu at the specified position.
void remove(`String`)	Remove the first occurrence of `item` from the `Choice` menu.
void removeAll()	Removes all items from the choice menu.
void removeItemListener(`ItemListener`)	Removes the specified item listener so that it no longer receives item events from this `Choice` menu.
void select(`int`)	Sets the selected item in this `Choice` menu to be the item at the specified position.
void select(`String`)	Sets the selected item in this `Choice` menu to be the item whose name is equal to the specified string.

Constructors

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

Methods

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 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.

addItemListener

public synchronized void addItemListener(ItemListener l) 
Adds the specified item listener to receive item events from this Choice menu. If l is null, no exception is thrown and no action is performed.

Parameters
l - the item listener.

See Also
ItemEvent
ItemListener
removeItemListener

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

countItems

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

public int countItems()

getAccessibleContext

public AccessibleContext getAccessibleContext() 
Get the AccessibleContext associated with this Choice. Creates a new context if necessary.

Returns
the AccessibleContext of this Choice

Overrides
getAccessibleContext in class Component

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

getItemCount

public int getItemCount() 
Returns the number of items in this Choice menu.

See Also
getItem

getListeners

public EventListener[] getListeners(Class listenerType) 
Return an array of all the listeners that were added to the Choice with addXXXListener(), where XXX is the name of the listenerType argument. For example, to get all of the ItemListener(s) for the given Choice c, one would write:
 ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.class))
 
If no such listener list exists, then an empty array is returned.
Parameters
listenerType - Type of listeners requested

Returns
all of the listeners of the specified type supported by this choice

Overrides
getListeners in class Component

getSelectedIndex

public int getSelectedIndex() 
Returns the index of the currently selected item.

See Also
getSelectedItem

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

insert

public 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.

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

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

remove

public void remove(int position) 
Removes an item from the choice menu at the specified position.

Parameters
position - the position of the item.

remove

public 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.

removeAll

public void removeAll() 
Removes all items from the choice menu.

See Also
remove

removeItemListener

public synchronized void removeItemListener(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.

Parameters
l - the item listener.

See Also
ItemEvent
ItemListener
addItemListener

select

public synchronized 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