Class java.awt.Checkbox - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.awt.Checkbox

java.lang.Object
   |
   +----java.awt.Component
           |
           +----java.awt.Checkbox

public class Checkbox
extends Component
implements ItemSelectable

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.

See Also:: GridLayout, CheckboxGroup

Checkbox(): Creates a check box with no label.
Checkbox(String): Creates a check box with the specified label.
Checkbox(String, boolean): Creates a check box with the specified label.
Checkbox(String, boolean, CheckboxGroup): Creates a check box with the specified label, in the specified check box group, and set to the specified state.
Checkbox(String, CheckboxGroup, boolean): Constructs a Checkbox with the specified label, set to the specified state, and in the specified check box group.

addItemListener(ItemListener): Adds the specified item listener to receive item events from this check box.
addNotify(): Creates the peer of the Checkbox.
getCheckboxGroup(): Determines this check box's group.
getLabel(): Gets the label of this check box.
getSelectedObjects(): Returns the an array (length 1) containing the checkbox label or null if the checkbox is not selected.
getState(): Determines whether this check box is in the "on" or "off" state.
paramString(): Returns the parameter string representing the state of this check box.
processEvent(AWTEvent): Processes events on this check box.
processItemEvent(ItemEvent): Processes item events occurring on this check box by dispatching them to any registered ItemListener objects.
removeItemListener(ItemListener): Removes the specified item listener so that the item listener no longer receives item events from this check box.
setCheckboxGroup(CheckboxGroup): Sets this check box's group to be the specified check box group.
setLabel(String): Sets this check box's label to be the string argument.
setState(boolean): Sets the state of this check box to the specified state.

Checkbox

 public Checkbox()

Creates a check box with no label. The state of this check box is set to "off," and it is not part of any check box group.

Checkbox

 public Checkbox(String label)

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.

Checkbox

 public Checkbox(String label,
                 boolean state)

Creates a check box with the specified label. The state of this check box is as specified by the state argument, and it 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.

Checkbox

 public Checkbox(String label,
                 boolean state,
                 CheckboxGroup group)

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.; state - the initial state of this check box.; group - a check box group for this check box, or null for no group.

Checkbox

 public Checkbox(String label,
                 CheckboxGroup group,
                 boolean state)

Constructs a Checkbox with the specified label, set to the specified state, and in the specified check box group.

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:: createCheckbox, 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

setLabel

 public synchronized 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

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.

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

getSelectedObjects

 public Object[] getSelectedObjects()

Returns the an array (length 1) containing the checkbox label or null if the checkbox is not selected.

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

setCheckboxGroup

 public void setCheckboxGroup(CheckboxGroup g)

Sets this check box's group to be 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.

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

addItemListener

 public synchronized void addItemListener(ItemListener l)

Adds the specified item listener to receive item events from this check box.

Parameters:: l - the item listener.
See Also:: ItemEvent, ItemListener, removeItemListener

removeItemListener

 public synchronized void removeItemListener(ItemListener l)

Removes the specified item listener so that the item listener no longer receives item events from this check box.

Parameters:: l - the item listener.
See Also:: ItemEvent, ItemListener, addItemListener

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.

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 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 via addItemListener.
Item events are enabled via enableEvents.

Parameters:: e - the item event.
See Also:: ItemEvent, ItemListener, addItemListener, enableEvents

paramString

 protected String paramString()

Returns the parameter string representing the state of this check box. This string is useful for debugging.

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

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