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java.awt
Class Checkbox

java.lang.Object
  extended by java.awt.Component
      extended by java.awt.Checkbox
All Implemented Interfaces:
ImageObserver, ItemSelectable, MenuContainer, Serializable, Accessible

public class Checkbox
extends Component
implements ItemSelectable, Accessible

A check box is a graphical component that can be in either an "on" (true) or "off" (false) state. Clicking on a check box changes its state from "on" to "off," or from "off" to "on."

The following code example creates a set of check boxes in a grid layout:


 setLayout(new GridLayout(3, 1));
 add(new Checkbox("one", null, true));
 add(new Checkbox("two"));
 add(new Checkbox("three"));
 

This image depicts the check boxes and grid layout created by this code example:

The following context describes the graphic.

The button labeled one is in the "on" state, and the other two are in the "off" state. In this example, which uses the GridLayout class, the states of the three check boxes are set independently.

Alternatively, several check boxes can be grouped together under the control of a single object, using the CheckboxGroup class. In a check box group, at most one button can be in the "on" state at any given time. Clicking on a check box to turn it on forces any other check box in the same group that is on into the "off" state.

Since:
JDK1.0
See Also:
GridLayout, CheckboxGroup, Serialized Form

Nested Class Summary
protected  class Checkbox.AccessibleAWTCheckbox
          This class implements accessibility support for the Checkbox class.
 
Nested classes/interfaces inherited from class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy
 
Field Summary
 
Fields inherited from class java.awt.Component
BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT
 
Fields inherited from interface java.awt.image.ImageObserver
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH
 
Constructor Summary
Checkbox()
          Creates a check box with an empty string for its label.
Checkbox(String label)
          Creates a check box with the specified label.
Checkbox(String label, boolean state)
          Creates a check box with the specified label and sets the specified state.
Checkbox(String label, boolean state, CheckboxGroup group)
          Constructs a Checkbox with the specified label, set to the specified state, and in the specified check box group.
Checkbox(String label, CheckboxGroup group, boolean state)
          Creates a check box with the specified label, in the specified check box group, and set to the specified state.
 
Method Summary
 void addItemListener(ItemListener l)
          Adds the specified item listener to receive item events from this check box.
 void addNotify()
          Creates the peer of the Checkbox.
 AccessibleContext getAccessibleContext()
          Gets the AccessibleContext associated with this Checkbox.
 CheckboxGroup getCheckboxGroup()
          Determines this check box's group.
 ItemListener[] getItemListeners()
          Returns an array of all the item listeners registered on this checkbox.
 String getLabel()
          Gets the label of this check box.
<T extends EventListener>
T[]
getListeners(Class<T> listenerType)
          Returns an array of all the objects currently registered as FooListeners upon this Checkbox.
 Object[] getSelectedObjects()
          Returns an array (length 1) containing the checkbox label or null if the checkbox is not selected.
 boolean getState()
          Determines whether this check box is in the "on" or "off" state.
protected  String paramString()
          Returns a string representing the state of this Checkbox.
protected  void processEvent(AWTEvent e)
          Processes events on this check box.
protected  void processItemEvent(ItemEvent e)
          Processes item events occurring on this check box by dispatching them to any registered ItemListener objects.
 void removeItemListener(ItemListener l)
          Removes the specified item listener so that the item listener no longer receives item events from this check box.
 void setCheckboxGroup(CheckboxGroup g)
          Sets this check box's group to the specified check box group.
 void setLabel(String label)
          Sets this check box's label to be the string argument.
 void setState(boolean state)
          Sets the state of this check box to the specified state.
 
Methods inherited from class java.awt.Component
action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBaseline, getBaselineResizeBehavior, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeys, getFocusTraversalKeysEnabled, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getMinimumSize, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPeer, getPreferredSize, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, invalidate, isBackgroundSet, isCursorSet, isDisplayable, isDoubleBuffered, isEnabled, isFocusable, isFocusCycleRoot, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isOpaque, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, layout, list, list, list, list, list, locate, location, lostFocus, minimumSize, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paint, paintAll, postEvent, preferredSize, prepareImage, prepareImage, print, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, update, validate
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Checkbox

public Checkbox()
         throws HeadlessException
Creates a check box with an empty string for its label. The state of this check box is set to "off," and it is not part of any check box group.

Throws:
HeadlessException - if GraphicsEnvironment.isHeadless() returns true
See Also:
GraphicsEnvironment.isHeadless()

Checkbox

public Checkbox(String label)
         throws HeadlessException
Creates a check box with the specified label. The state of this check box is set to "off," and it is not part of any check box group.

Parameters:
label - a string label for this check box, or null for no label.
Throws:
HeadlessException - if GraphicsEnvironment.isHeadless returns true
See Also:
GraphicsEnvironment.isHeadless()

Checkbox

public Checkbox(String label,
                boolean state)
         throws HeadlessException
Creates a check box with the specified label and sets the specified state. This check box is not part of any check box group.

Parameters:
label - a string label for this check box, or null for no label
state - the initial state of this check box
Throws:
HeadlessException - if GraphicsEnvironment.isHeadless returns true
See Also:
GraphicsEnvironment.isHeadless()

Checkbox

public Checkbox(String label,
                boolean state,
                CheckboxGroup group)
         throws HeadlessException
Constructs a Checkbox with the specified label, set to the specified state, and in the specified check box group.

Parameters:
label - a string label for this check box, or null for no label.
state - the initial state of this check box.
group - a check box group for this check box, or null for no group.
Throws:
HeadlessException - if GraphicsEnvironment.isHeadless returns true
Since:
JDK1.1
See Also:
GraphicsEnvironment.isHeadless()

Checkbox

public Checkbox(String label,
                CheckboxGroup group,
                boolean state)
         throws HeadlessException
Creates a check box with the specified label, in the specified check box group, and set to the specified state.

Parameters:
label - a string label for this check box, or null for no label.
group - a check box group for this check box, or null for no group.
state - the initial state of this check box.
Throws:
HeadlessException - if GraphicsEnvironment.isHeadless returns true
Since:
JDK1.1
See Also:
GraphicsEnvironment.isHeadless()
Method Detail

addNotify

public void addNotify()
Creates the peer of the Checkbox. The peer allows you to change the look of the Checkbox without changing its functionality.

Overrides:
addNotify in class Component
See Also:
Toolkit.createCheckbox(java.awt.Checkbox), Component.getToolkit()

getLabel

public String getLabel()
Gets the label of this check box.

Returns:
the label of this check box, or null if this check box has no label.
See Also:
setLabel(String)

setLabel

public void setLabel(String label)
Sets this check box's label to be the string argument.

Parameters:
label - a string to set as the new label, or null for no label.
See Also:
getLabel()

getState

public boolean getState()
Determines whether this check box is in the "on" or "off" state. The boolean value true indicates the "on" state, and false indicates the "off" state.

Returns:
the state of this check box, as a boolean value
See Also:
setState(boolean)

setState

public void setState(boolean state)
Sets the state of this check box to the specified state. The boolean value true indicates the "on" state, and false indicates the "off" state.

Note that this method should be primarily used to initialize the state of the checkbox. Programmatically setting the state of the checkbox will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

Parameters:
state - the boolean state of the check box
See Also:
getState()

getSelectedObjects

public Object[] getSelectedObjects()
Returns an array (length 1) containing the checkbox label or null if the checkbox is not selected.

Specified by:
getSelectedObjects in interface ItemSelectable
See Also:
ItemSelectable

getCheckboxGroup

public CheckboxGroup getCheckboxGroup()
Determines this check box's group.

Returns:
this check box's group, or null if the check box is not part of a check box group.
See Also:
setCheckboxGroup(CheckboxGroup)

setCheckboxGroup

public void setCheckboxGroup(CheckboxGroup g)
Sets this check box's group to the specified check box group. If this check box is already in a different check box group, it is first taken out of that group.

If the state of this check box is true and the new group already has a check box selected, this check box's state is changed to false. If the state of this check box is true and the new group has no check box selected, this check box becomes the selected checkbox for the new group and its state is true.

Parameters:
g - the new check box group, or null to remove this check box from any check box group
See Also:
getCheckboxGroup()

addItemListener

public void addItemListener(ItemListener l)
Adds the specified item listener to receive item events from this check box. Item events are sent to listeners in response to user input, but not in response to calls to setState(). 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.

Specified by:
addItemListener in interface ItemSelectable
Parameters:
l - the item listener
Since:
JDK1.1
See Also:
removeItemListener(java.awt.event.ItemListener), getItemListeners(), setState(boolean), ItemEvent, ItemListener

removeItemListener

public void removeItemListener(ItemListener l)
Removes the specified item listener so that the item listener no longer receives item events from this check box. 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.

Specified by:
removeItemListener in interface ItemSelectable
Parameters:
l - the item listener
Since:
JDK1.1
See Also:
addItemListener(java.awt.event.ItemListener), getItemListeners(), ItemEvent, ItemListener

getItemListeners

public ItemListener[] getItemListeners()
Returns an array of all the item listeners registered on this checkbox.

Returns:
all of this checkbox's ItemListeners or an empty array if no item listeners are currently registered
Since:
1.4
See Also:
addItemListener(java.awt.event.ItemListener), removeItemListener(java.awt.event.ItemListener), ItemEvent, ItemListener

getListeners

public <T extends EventListener> T[] getListeners(Class<T> listenerType)
Returns an array of all the objects currently registered as FooListeners upon this Checkbox. 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 Checkbox 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.

Overrides:
getListeners in class Component
Parameters:
listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener
Returns:
an array of all objects registered as FooListeners on this checkbox, or an empty array if no such listeners have been added
Throws:
ClassCastException - if listenerType doesn't specify a class or interface that implements java.util.EventListener
Since:
1.3
See Also:
getItemListeners()

processEvent

protected void processEvent(AWTEvent e)
Processes events on this check box. If the event is an instance of ItemEvent, this method 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.

Overrides:
processEvent in class Component
Parameters:
e - the event
Since:
JDK1.1
See Also:
ItemEvent, processItemEvent(java.awt.event.ItemEvent)

processItemEvent

protected void processItemEvent(ItemEvent e)
Processes item events occurring on this check box 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:

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

Parameters:
e - the item event
Since:
JDK1.1
See Also:
ItemEvent, ItemListener, addItemListener(java.awt.event.ItemListener), Component.enableEvents(long)

paramString

protected String paramString()
Returns a string representing the state of this Checkbox. 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.

Overrides:
paramString in class Component
Returns:
the parameter string of this check box

getAccessibleContext

public AccessibleContext getAccessibleContext()
Gets the AccessibleContext associated with this Checkbox. For checkboxes, the AccessibleContext takes the form of an AccessibleAWTCheckbox. A new AccessibleAWTCheckbox is created if necessary.

Specified by:
getAccessibleContext in interface Accessible
Overrides:
getAccessibleContext in class Component
Returns:
an AccessibleAWTCheckbox that serves as the AccessibleContext of this Checkbox
Since:
1.3

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