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JavaTM 2 Platform Standard Ed. 5.0 |
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java.lang.Object java.awt.Component java.awt.Checkbox
public class Checkbox
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.
GridLayout
,
CheckboxGroup
,
Serialized FormNested 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.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 |
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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. |
|
|
getListeners(Class<T> listenerType)
Returns an array of all the objects currently registered as FooListener s
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.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
---|
public Checkbox() throws HeadlessException
HeadlessException
- if GraphicsEnvironment.isHeadless()
returns trueGraphicsEnvironment.isHeadless()
public Checkbox(String label) throws HeadlessException
label
- a string label for this check box,
or null
for no label.
HeadlessException
- if
GraphicsEnvironment.isHeadless
returns true
GraphicsEnvironment.isHeadless()
public Checkbox(String label, boolean state) throws HeadlessException
label
- a string label for this check box,
or null
for no labelstate
- the initial state of this check box
HeadlessException
- if
GraphicsEnvironment.isHeadless
returns true
GraphicsEnvironment.isHeadless()
public Checkbox(String label, boolean state, CheckboxGroup group) throws HeadlessException
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.
HeadlessException
- if
GraphicsEnvironment.isHeadless
returns true
GraphicsEnvironment.isHeadless()
public Checkbox(String label, CheckboxGroup group, boolean state) throws HeadlessException
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.
HeadlessException
- if
GraphicsEnvironment.isHeadless
returns true
GraphicsEnvironment.isHeadless()
Method Detail |
---|
public void addNotify()
addNotify
in class Component
Toolkit.createCheckbox(java.awt.Checkbox)
,
Component.getToolkit()
public String getLabel()
null
if this check box has no label.setLabel(String)
public void setLabel(String label)
label
- a string to set as the new label, or
null
for no label.getLabel()
public boolean getState()
true
indicates the "on" state,
and false
indicates the "off" state.
setState(boolean)
public void setState(boolean state)
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.
state
- the boolean state of the check boxgetState()
public Object[] getSelectedObjects()
getSelectedObjects
in interface ItemSelectable
ItemSelectable
public CheckboxGroup getCheckboxGroup()
null
if the check box is not part of a check box group.setCheckboxGroup(CheckboxGroup)
public void setCheckboxGroup(CheckboxGroup g)
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
.
g
- the new check box group, or null
to remove this check box from any check box groupgetCheckboxGroup()
public void addItemListener(ItemListener l)
addItemListener
in interface ItemSelectable
l
- the item listenerremoveItemListener(java.awt.event.ItemListener)
,
getItemListeners()
,
setState(boolean)
,
ItemEvent
,
ItemListener
public void removeItemListener(ItemListener l)
removeItemListener
in interface ItemSelectable
l
- the item listeneraddItemListener(java.awt.event.ItemListener)
,
getItemListeners()
,
ItemEvent
,
ItemListener
public ItemListener[] getItemListeners()
ItemListener
s
or an empty array if no item
listeners are currently registeredaddItemListener(java.awt.event.ItemListener)
,
removeItemListener(java.awt.event.ItemListener)
,
ItemEvent
,
ItemListener
public <T extends EventListener> T[] getListeners(Class<T> listenerType)
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.
getListeners
in class Component
listenerType
- the type of listeners requested; this parameter
should specify an interface that descends from
java.util.EventListener
FooListener
s on this checkbox,
or an empty array if no such
listeners have been added
ClassCastException
- if listenerType
doesn't specify a class or interface that implements
java.util.EventListener
getItemListeners()
protected void processEvent(AWTEvent e)
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.
processEvent
in class Component
e
- the eventItemEvent
,
processItemEvent(java.awt.event.ItemEvent)
protected void processItemEvent(ItemEvent e)
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.
e
- the item eventItemEvent
,
ItemListener
,
addItemListener(java.awt.event.ItemListener)
,
Component.enableEvents(long)
protected String paramString()
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
.
paramString
in class Component
public AccessibleContext getAccessibleContext()
getAccessibleContext
in interface Accessible
getAccessibleContext
in class Component
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JavaTM 2 Platform Standard Ed. 5.0 |
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Copyright 2004 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.