corejava第10版

corejava第10版/v1ch07/except/ExceptTest.java

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+package except;
+
+import java.awt.EventQueue;
+import java.awt.event.*;
+import java.io.*;
+import java.nio.file.*;
+import java.util.*;
+import javax.swing.*;
+
+/**
+ * @version 1.34 2015-08-20
+ * @author Cay Horstmann
+ */
+public class ExceptTest
+{
+   public static void main(String[] args)
+   {
+      EventQueue.invokeLater(() ->
+            {
+               JFrame frame = new ExceptTestFrame();
+               frame.setTitle("ExceptTest");   
+               frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+               frame.setVisible(true);
+            });
+   }
+}
+
+/**
+ * A frame with a panel for testing various exceptions
+ */
+class ExceptTestFrame extends JFrame
+{
+   public ExceptTestFrame()
+   {
+      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
+{
+   private ButtonGroup group;
+   private JTextField textField;
+   private double[] a = new double[10];
+
+   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)
+            {
+               System.out.println(textField.getAction().toString());
+            }
+         });
+
+      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];
+               System.out.println(n);
+            }
+         });
+
+      addRadioButton("No such file", new ActionListener()
+         {
+            public void actionPerformed(ActionEvent event)
+            {
+               try
+               {
+                  System.out.println(
+                     new Scanner(Paths.get("woozle.txt"), "UTF-8").next());
+               }
+               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);
+   }
+}