Writing Classes - Java Software Solutions: Foundations of Program Design - page 194

LISTING 4.11 continued

//-----------------------------------------------------------------
// Constructor: Sets up the GUI.
//-----------------------------------------------------------------
public PushCounterPanel ()
{
count = 0;

push = new JButton ("Push Me!");
push.addActionListener (new ButtonListener());

label = new JLabel ("Pushes: " + count);

add (push);
add (label);

setPreferredSize ( new Dimension(300, 40));
setBackground (Color.cyan);
}

//*****************************************************************
// Represents a listener for button push (action) events.
//*****************************************************************
private class ButtonListener implements ActionListener
{
//--------------------------------------------------------------
// Updates the counter and label when the button is pushed.
//--------------------------------------------------------------
public void actionPerformed (ActionEvent event)
{
count++;
label.setText("Pushes: " + count);
}
}
}

The PushCounterPanel constructor sets up the GUI. The call to the JButton
constructor takes a String parameter that specifies the text shown on the button.
The button and the label are added to the panel.
The only event of interest in this program occurs when the button is pushed. To
respond to the event, we must create a listener object for that event, so we must
write a class that represents the listener.