Java: Example - InchesToCm

// InchesToCm.java -- converts feet and inches to centimeters

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

////////////////////////////////////////////////////////////////// InchesToCm
/** InchesToCm contains main program to convert feet an inches 
 *  to centimeters.
 * @author Fred Swartz
 * @version 2004-04-25
 */
class InchesToCm {
    /** Create window containing InchesToCmGUI panel. */
    public static void main(String[] args) {
        JFrame win = new JFrame();
        win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        win.setTitle("Inches To Centimeters");
        win.setContentPane(new InchesToCmGUI());
        win.pack();
        win.setVisible(true);
    }//end main
}//endclass InchesToCm

// InchesToCmGUI.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

/** Subclass JPanel to create GUI for ft+inches to cm conversion.*/
class InchesToCmGUI extends JPanel {
    private JTextField _feetField        = new JTextField(4);
    private JTextField _inchesField      = new JTextField(4);
    private JTextField _centimetersField = new JTextField(5);

    //======================================================= constructor
    public InchesToCmGUI() {
        JButton equalsButton = new JButton("=");
        equalsButton.addActionListener(new ConvertListener());

        //-- Layout components
        this.setLayout(new FlowLayout());
        this.add(new JLabel("Feet"));
        this.add(_feetField);
        this.add(new JLabel("Inches"));
        this.add(_inchesField);
        this.add(equalsButton);
        this.add(new JLabel("Centimeters"));
        this.add(_centimetersField);
    }//end constructor
    
    
    ///////////////////////////////////////// innner class ConvertListener
    /** Listener class to convert ft+inches to cm. */
    class ConvertListener implements ActionListener {
       public void actionPerformed(ActionEvent e) {
           try {
               double ftVal = Double.parseDouble(_feetField.getText());
               double inVal = Double.parseDouble(_inchesField.getText());
               _centimetersField.setText("" + (2.54 * (12*ftVal + inVal)));
           } catch (NumberFormatException ex) {
               _centimetersField.setText("ERROR");
           }
       }
    }//end inner class

}//endclass