validation.java

《A first book of java》by Gary J.Bronson 北大出版社

import java.text.*;  // need this for formatting
import javax.swing.*;
import java.awt.event.*;
import java.awt.Container;  // need this to add controls
import java.awt.*;  // need this for layout manager
public class Validation extends JFrame
{
  private JFrame mainFrame;
  private JButton exitButton;
  private JTextField inputField;
  private JTextField messageField;
  private JLabel inputLabel;
  public Validation() // a constructor
  {
    mainFrame = new JFrame("Input Validation");
      // create all components
    exitButton = new JButton("Exit");
    inputLabel = new JLabel("Enter an integer number:");
    inputField = new JTextField(5);
    messageField = new JTextField(20);
      // get the content pane 
    Container c = mainFrame.getContentPane(); 
      // set the layout manager
    c.setLayout(new FlowLayout());
    
      // add the components to the ContentPane 
    c.add(inputLabel);
    c.add(inputField);
    c.add(exitButton);
    c.add(messageField);
    
      // create accelerator keys
    exitButton.setMnemonic('x');
    mainFrame.setSize(250,125);
       // define and register window event handler
    mainFrame.addWindowListener(new WindowAdapter()
    {
      public void windowClosing(WindowEvent e) {System.exit(0);}
    });
    
      // create and register the button event handler
    ExitButtonHandler ehandler = new ExitButtonHandler();  // instantiate a handler
    exitButton.addActionListener(ehandler);  // register the handler    
    mainFrame.show();
  } 
     // inner class for the exit button event handler
  class ExitButtonHandler implements ActionListener
  {
    public void actionPerformed(ActionEvent e)
    {
      System.exit(0);
    }
  }  // end of button listener class
  public static void main(String args[])
  {
    new Validation();  // instantiate a GUI object 
  }
}  // end of class