It’s appropriate to use an anonymous inner class if you are going to use the class only once. In the Factorial program in Figures 17.8a and 17.8b, we use the listener object twice, so that listener object needed to have a name. However, we used that object’s class only once, to instantiate that one object. Therefore, that object’s class did not need to have a name, and we could have used an anonymous class to create our listener object. For this exercise, modify the Factorial program to use an anonymous ActionListener class instead of the named Listener class.

Figures 17.8a:

Figures 17.8b:

Transcribed Image Text:

/********************************** * FactorialButton.java * Dean & Dean * * When user clicks button or presses Enter with cursor in input * text box, entered number's factorial displays in output text box. ******************************************************************/ import javax.swing. *; import java.awt. *; import java.awt.event. *; public class Factorial Button extends JFrame { private static final int WIDTH = 300; private static final int HEIGHT = 100; private JTextField xBox; // holds user entry private JTextField xfBox; // holds generated factorial //************************** public Factorial Button() ( createContents(); setVisible(true); setTitle("Factorial Calculator"); setSize (WIDTH, HEIGHT); set Layout (new FlowLayout()); set DefaultCloseOperation (EXIT_ON_CLOSE); } // end FactorialButton constructor //************ ***************************** ******* private void createContents() ( ******* xBox= new JTextField (2); xfBox= new JTextField(10); xfBox.setEditable(false); JLabel xLabel= new JLabel("x:"); JLabel xfLabel= new JLabel("x! :"); JButton btn = new JButton("Factorial"); Listener listener = new Listener(); add (x Label); add(xBox); add(xfLabel); add (xfBox); add (btn); xBox. addActionListener(listener); btn.addActionListener(listener); } // end create Contents ********************* ************ Here, we register the same listener with two different components.