- java.lang.Object
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- java.awt.Component
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- java.awt.Checkbox
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- 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 theGridLayout
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
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Nested Class Summary
Nested Classes Modifier and Type Class and Description protected class
Checkbox.AccessibleAWTCheckbox
This class implements accessibility support for theCheckbox
class.-
Nested classes/interfaces inherited from class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy
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Field Summary
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Fields inherited from class java.awt.Component
BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT
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Constructor Summary
Constructors Constructor and 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.
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Method Summary
Methods Modifier and Type Method and 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>
T[]getListeners(Class<T> listenerType)
Returns an array of all the objects currently registered asFooListener
s upon thisCheckbox
.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 thisCheckbox
.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 registeredItemListener
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, revalidate, 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
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Constructor Detail
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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()
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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()
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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 labelstate
- the initial state of this check box- Throws:
HeadlessException
- ifGraphicsEnvironment.isHeadless
returnstrue
- See Also:
GraphicsEnvironment.isHeadless()
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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:
- JDK1.1
- See Also:
GraphicsEnvironment.isHeadless()
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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:
- JDK1.1
- See Also:
GraphicsEnvironment.isHeadless()
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Method Detail
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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:
Toolkit.createCheckbox(java.awt.Checkbox)
,Component.getToolkit()
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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)
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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()
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getState
public boolean getState()
Determines whether this check box is in the "on" or "off" state. The boolean valuetrue
indicates the "on" state, andfalse
indicates the "off" state.- Returns:
- the state of this check box, as a boolean value
- See Also:
setState(boolean)
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setState
public void setState(boolean state)
Sets the state of this check box to the specified state. The boolean valuetrue
indicates the "on" state, andfalse
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 anItemEvent
is by user interaction.- Parameters:
state
- the boolean state of the check box- See Also:
getState()
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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
- See Also:
ItemSelectable
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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)
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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 tofalse
. If the state of this check box istrue
and the new group has no check box selected, this check box becomes the selected checkbox for the new group and its state istrue
.- Parameters:
g
- the new check box group, ornull
to remove this check box from any check box group- See Also:
getCheckboxGroup()
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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:
- JDK1.1
- See Also:
removeItemListener(java.awt.event.ItemListener)
,getItemListeners()
,setState(boolean)
,ItemEvent
,ItemListener
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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:
- JDK1.1
- See Also:
addItemListener(java.awt.event.ItemListener)
,getItemListeners()
,ItemEvent
,ItemListener
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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
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getListeners
public <T extends EventListener> T[] getListeners(Class<T> listenerType)
Returns an array of all the objects currently registered asFooListener
s upon thisCheckbox
.FooListener
s are registered using theaddFooListener
method.You can specify the
listenerType
argument with a class literal, such asFooListener.class
. For example, you can query aCheckbox
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
- 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()
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processEvent
protected void processEvent(AWTEvent e)
Processes events on this check box. If the event is an instance ofItemEvent
, this method invokes theprocessItemEvent
method. Otherwise, it calls its superclass'sprocessEvent
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:
- JDK1.1
- See Also:
ItemEvent
,processItemEvent(java.awt.event.ItemEvent)
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processItemEvent
protected void processItemEvent(ItemEvent e)
Processes item events occurring on this check box by dispatching them to any registeredItemListener
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:
- JDK1.1
- See Also:
ItemEvent
,ItemListener
,addItemListener(java.awt.event.ItemListener)
,Component.enableEvents(long)
- An
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paramString
protected String paramString()
Returns a string representing the state of thisCheckbox
. 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 benull
.- Overrides:
paramString
in classComponent
- Returns:
- the parameter string of this check box
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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
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