dividebyzerotest.java

金旭亮的java教案

//  DivideByZeroTest.java
// A simple exception handling example.
// Checking for a divide-by-zero-error.
import java.text.DecimalFormat;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class DivideByZeroTest extends JFrame
                              implements ActionListener {
   private JTextField input1, input2, output;
   private int number1, number2;
   private double result;

   // Initialization
   public DivideByZeroTest()
   {
      super( "Demonstrating Exceptions" );

      Container c = getContentPane();
      c.setLayout( new GridLayout( 3, 2 ) );

      c.add( new JLabel( "Enter numerator ",
                         SwingConstants.RIGHT ) );
      input1 = new JTextField( 10 );
      c.add( input1 );

      c.add(
         new JLabel( "Enter denominator and press Enter ",
                     SwingConstants.RIGHT ) );
      input2 = new JTextField( 10 );
      c.add( input2 );
      input2.addActionListener( this );

      c.add( new JLabel( "RESULT ", SwingConstants.RIGHT ) );
      output = new JTextField();
      c.add( output );

      setSize( 425, 100 );
      show();
   }

   // Process GUI events
   public void actionPerformed( ActionEvent e )
   {
      DecimalFormat precision3 = new DecimalFormat( "0.000" );

      output.setText( "" ); // empty the output JTextField

      try {         
         number1 = Integer.parseInt( input1.getText() );
         number2 = Integer.parseInt( input2.getText() );

         result = quotient( number1, number2 ); //有可能引发异常
         output.setText( precision3.format( result ) );
      }
      catch ( NumberFormatException nfe ) {
         JOptionPane.showMessageDialog( this,
            "You must enter two integers",
            "Invalid Number Format",
            JOptionPane.ERROR_MESSAGE );
      }
      catch ( DivideByZeroException dbze ) {
         JOptionPane.showMessageDialog( this, dbze.toString(),
            "Attempted to Divide by Zero",
            JOptionPane.ERROR_MESSAGE );
      }
   }

   // Definition of method quotient. Used to demonstrate
   // throwing an exception when a divide-by-zero error
   // is encountered.
   public double quotient( int numerator, int denominator )
      throws DivideByZeroException
   {
      if ( denominator == 0 )
         throw new DivideByZeroException();

      return ( double ) numerator / denominator;
   }

   public static void main( String args[] )
   {
      DivideByZeroTest app = new DivideByZeroTest();

      app.addWindowListener(
         new WindowAdapter() {
            public void windowClosing( WindowEvent e )
            {
               e.getWindow().dispose();
               System.exit( 0 );
            }
         }
      );
   }
}