Class Checkbox
- java.lang.Object
-
- java.awt.Component
-
- 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 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:
- 1.0
- See Also:
-
GridLayout
,CheckboxGroup
, Serialized Form
Nested Class Summary
Modifier and Type | Class | Description |
---|---|---|
protected class | Checkbox.AccessibleAWTCheckbox | This class implements accessibility support for the |
Nested classes/interfaces declared in class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy
Field Summary
Fields declared in class java.awt.Component
accessibleContext, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT
Fields declared in interface java.awt.image.ImageObserver
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH
Constructor Summary
Constructor | Description |
---|---|
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
Modifier and Type | Method | Description |
---|---|---|
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> | getListeners(Class<T> listenerType) | Returns an array of all the objects currently registered as |
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 |
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 |
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 declared in 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, 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, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, revalidate, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setMixingCutoutShape, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, update, validate
Methods declared in 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, ornull
for no label. - Throws:
-
HeadlessException
- ifGraphicsEnvironment.isHeadless
returnstrue
- 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, ornull
for no label -
state
- the initial state of this check box - Throws:
-
HeadlessException
- ifGraphicsEnvironment.isHeadless
returnstrue
- 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, ornull
for no label. -
state
- the initial state of this check box. -
group
- a check box group for this check box, ornull
for no group. - Throws:
-
HeadlessException
- ifGraphicsEnvironment.isHeadless
returnstrue
- Since:
- 1.1
- 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, ornull
for no label. -
group
- a check box group for this check box, ornull
for no group. -
state
- the initial state of this check box. - Throws:
-
HeadlessException
- ifGraphicsEnvironment.isHeadless
returnstrue
- Since:
- 1.1
- 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 classComponent
- See Also:
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, ornull
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 interfaceItemSelectable
- Returns:
- the list of selected objects, or
null
- 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, ornull
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 interfaceItemSelectable
- Parameters:
-
l
- the item listener - Since:
- 1.1
- 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 interfaceItemSelectable
- Parameters:
-
l
- the item listener - Since:
- 1.1
- 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
ItemListener
s 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 FooListener
s upon this Checkbox
. FooListener
s 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 classComponent
- Type Parameters:
-
T
- the type of the listeners - Parameters:
-
listenerType
- the type of listeners requested; this parameter should specify an interface that descends fromjava.util.EventListener
- Returns:
- an array of all objects registered as
FooListener
s on this checkbox, or an empty array if no such listeners have been added - Throws:
-
ClassCastException
- iflistenerType
doesn't specify a class or interface that implementsjava.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 classComponent
- Parameters:
-
e
- the event - Since:
- 1.1
- 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:
- An
ItemListener
object is registered viaaddItemListener
. - Item events are enabled via
enableEvents
.
Note that if the event parameter is null
the behavior is unspecified and may result in an exception.
- Parameters:
-
e
- the item event - Since:
- 1.1
- 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 classComponent
- 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 interfaceAccessible
- Overrides:
-
getAccessibleContext
in classComponent
- Returns:
- an AccessibleAWTCheckbox that serves as the AccessibleContext of this Checkbox
- Since:
- 1.3