which button has been pushed by using its object reference. It is also possible to set the
action command string associated with a button to something other than its label by calling
setActionCommand( ). This method changes the action command string, but does not affect
the string used to label the button. Thus, setting the action command enables the action
command and the label of a button to differ.
Applying Check Boxes
A check box is a control that is used to turn an option on or off. It consists of a small box that
can either contain a check mark or not. There is a label associated with each check box that
describes what option the box represents. You change the state of a check box by clicking on
it. Check boxes can be used individually or as part of a group. Check boxes are objects of the
Checkbox class.
Checkbox supports these constructors:
Checkbox( ) throws HeadlessException
Checkbox(String str) throws HeadlessException
Checkbox(String str, boolean on) throws HeadlessException
Checkbox(String str, boolean on, CheckboxGroup cbGroup) throws HeadlessException
Checkbox(String str, CheckboxGroup cbGroup, boolean on) throws HeadlessException
The first form creates a check box whose label is initially blank. The state of the check box is
unchecked. The second form creates a check box whose label is specified by str. The state of
the check box is unchecked. The third form allows you to set the initial state of the check
box. If on is true, the check box is initially checked; otherwise, it is cleared. The fourth and
fifth forms create a check box whose label is specified by str and whose group is specified
by cbGroup. If this check box is not part of a group, then cbGroup must be null. (Check box
groups are described in the next section.) The value of on determines the initial state of the
check box.
To retrieve the current state of a check box, call getState( ). To set its state, call
setState( ). You can obtain the current label associated with a check box by calling
getLabel( ). To set the label, call setLabel( ). These methods are as follows:
boolean getState( )
void setState(boolean on)
String getLabel( )
void setLabel(String str)
Here, if on is true, the box is checked. If it is false, the box is cleared. The string passed in str
becomes the new label associated with the invoking check box.
Handling Check Boxes
Each time a check box is selected or deselected, an item event is generated. This is sent to
any listeners that previously registered an interest in receiving item event notifications from
that component. Each listener implements the ItemListener interface. That interface defines
the itemStateChanged( ) method. An ItemEvent object is supplied as the argument to this
method. It contains information about the event (for example, whether it was a selection or
deselection).
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