Many applications use an audible “beep” sound to signal that an error has occurred or to get the user’s attention for some reason. For example, a user interface that allows the user to enter only a certain number or type of characters into a field (i.e., a field that can only contain numeric values) may “beep” whenever a user presses a key representing an invalid character or when the field is already “full.” To generate beeps in Java, you must first get a reference to an instance of java.awt.Toolkit, at which time you can call its beep() method. For example, the code shown here will generate a beep whenever the displayed Button is pressed:

 import java.awt.*;import java.awt.event.*;public class BeepTest extends Frame implements ActionListener {	public static void main(String[] args) {		BeepTest bt = new BeepTest();		bt.setSize(400, 300);		bt.setVisible(true);	}  //  public static void main(String[] args)	public BeepTest() {		setLayout(new FlowLayout());		Button b = new Button("Click To Beep");		b.addActionListener(this);		add(b);	}  //  public BeepTest()	public void actionPerformed(ActionEvent event) {		Toolkit tk = Toolkit.getDefaultToolkit();		tk.beep();	}  //  public void actionPerformed()}  //  public class BeepTest extends Frame()

In the actionPerformed() method, a reference is obtained to the default Toolkit instance, and its beep() method is called. You can use this technique to enhance your user interface with beep sounds where appropriate.