excepttest.java

Java编程例子(全新)演示基础的Java 功能,例如类,对象的使用,过程的调用,.

/**
   @version 1.32 2004-05-10
   @author Cay Horstmann
*/

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

public class ExceptTest
{  
   public static void main(String[] args)
   {  
      ExceptTestFrame frame = new ExceptTestFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);  
   }
}

/**
   A frame with a panel for testing various exceptions
*/
class ExceptTestFrame extends JFrame
{
   public ExceptTestFrame()
   {
      setTitle("ExceptTest");
      ExceptTestPanel panel = new ExceptTestPanel();
      add(panel);
      pack();
   }
}

/**
   A panel with radio buttons for running code snippets
   and studying their exception behavior
*/
class ExceptTestPanel extends Box
{
   public ExceptTestPanel()
   {  
      super(BoxLayout.Y_AXIS);
      group = new ButtonGroup();

      // add radio buttons for code snippets

      addRadioButton("Integer divide by zero", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               a[1] = 1 / (a.length - a.length);
            }
         });

      addRadioButton("Floating point divide by zero", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               a[1] = a[2] / (a[3] - a[3]);
            }
         });

      addRadioButton("Array bounds", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               a[1] = a[10];
            }
         });

      addRadioButton("Bad cast", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               a = (double[])event.getSource();
            }
         });

      addRadioButton("Null pointer", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               event = null;
               System.out.println(event.getSource());
            }
         });

      addRadioButton("sqrt(-1)", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               a[1] = Math.sqrt(-1);
            }
         });

      addRadioButton("Overflow", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               a[1] = 1000 * 1000 * 1000 * 1000;
               int n = (int) a[1];
            }
         });

      addRadioButton("No such file", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               try
               {
                  InputStream in = new FileInputStream("woozle.txt");
               }
               catch (IOException e)
               {
                  textField.setText(e.toString());
               }
            }
         });

      addRadioButton("Throw unknown", new 
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               throw new UnknownError();
            }
         });

      // add the text field for exception display
      textField = new JTextField(30);
      add(textField);
   }

   /**
      Adds a radio button with a given listener to the 
      panel. Traps any exceptions in the actionPerformed
      method of the listener.
      @param s the label of the radio button
      @param listener the action listener for the radio button
   */
   private void addRadioButton(String s, ActionListener listener)
   {  
      JRadioButton button = new JRadioButton(s, false)
         {
            // the button calls this method to fire an 
            // action event. We override it to trap exceptions
            protected void fireActionPerformed(ActionEvent event)
            {
               try
               {
                  textField.setText("No exception");
                  super.fireActionPerformed(event);
               }
               catch (Exception e)
               {
                  textField.setText(e.toString());
               }
            }
         };

      button.addActionListener(listener);
      add(button);
      group.add(button);
   }

   private ButtonGroup group;
   private JTextField textField;
   private double[] a = new double[10];
}