exercise13_5.java

Introduction to java programming 一书中所有编程练习部分的源码

// Exercise13_5.java: Convert Mile to Kilometer and vice versa
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Exercise13_5 extends JFrame implements ActionListener {
  private JTextField jtfMile = new JTextField(10);
  private JTextField jtfKilometer = new JTextField(10);

  // Main method
  public static void main(String[] args) {
    Exercise13_5 frame = new Exercise13_5();
    frame.pack();
    frame.setTitle("Exercise13_5");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }

  public Exercise13_5() {
    // Panel p1 to hold labels and text fields
    JPanel p = new JPanel();
    p.setLayout(new GridLayout(2, 2));
    p.add(new JLabel("Mile"));
    p.add(jtfMile);
    p.add(new JLabel("Kilometer"));
    p.add(jtfKilometer);

    jtfMile.setHorizontalAlignment(JTextField.RIGHT);
    jtfKilometer.setHorizontalAlignment(JTextField.RIGHT);

    // Add p to the frame
    getContentPane().add(p);

    // Register listener
    jtfMile.addActionListener(this);
    jtfKilometer.addActionListener(this);
  }

  // Handle ActionEvent
  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == jtfMile) {
      double mile = new Double(jtfMile.getText().trim()).doubleValue();
      double kilometer = mile / 0.6241;
      jtfKilometer.setText(new Double(kilometer).toString());
    }
    else {
      double kilometer = new Double(jtfKilometer.getText().trim()).doubleValue();
      double mile = 0.6241 * kilometer;
      jtfMile.setText(new Double(mile).toString());
    }
  }
}