Conditionals and Loops - Java Software Solutions: Foundations of Program Design - page 251

LISTING 5.13 continued

//*****************************************************************
// Represents a listener for both buttons.
//*****************************************************************
private class ButtonListener implements ActionListener
{
//--------------------------------------------------------------
// Determines which button was pressed and sets the label
// text accordingly.
//--------------------------------------------------------------
public void actionPerformed (ActionEvent event)
{
if (event.getSource() == left)
label.setText("Left");
else
label.setText("Right");
}
}
}

We could have created two separate listener classes, one to listen to the left but-
ton and another to listen to the right. In that case, the actionPerformed method
would not have to determine the source of the event. Whether to have multiple
listeners or determine the event source when it occurs is a design decision that
should be made depending on the situation.
Note that the two buttons are put on the same panel called buttonPanel ,
which is separate from the panel represented by the LeftRightPanel class. By
putting both buttons on one panel, we can guarantee their visual relationship to
each other even when the frame is resized in various ways. For buttons labeled
Left and Right, that may be important.

5.8 Check Boxes and Radio Buttons

A push button, as defined by the JButton class, is only one kind of button that
we can use in a Java GUI. Two other kinds are check boxes and radio buttons.
Let's look at these in detail.

Check Boxes
A check box is a button that can be toggled on or off using the mouse, indicat-
ing that a particular boolean condition is set or unset. For example, a check box