creditinquiry.java

用JAVA开发的交易处理程序

// Fig. 15.7: CreditInquiry.java
// This program reads a file sequentially and displays the
// contents in a text area based on the type of account the
// user requests (credit balance, debit balance or zero balance.
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;

public class CreditInquiry extends Frame
             implements ActionListener {

   // application window components
   private TextArea recordDisplay;
   private Button done, credit, debit, zero;                    
   private Panel buttonPanel;         

   private RandomAccessFile input;
   private String accountType;

   public CreditInquiry()
   {
      super( "Credit Inquiry Program" );

      // Open the file
      try {
         input = new RandomAccessFile( "client.dat", "r" );
      }
      catch ( IOException e ) {
         System.err.println( e.toString() );
         System.exit( 1 );
      }

      setSize( 400, 150 );

      // create the components of the Frame
      buttonPanel = new Panel();
      credit = new Button( "Credit balances" );
      credit.addActionListener( this );
      buttonPanel.add( credit );
      debit = new Button( "Debit balances" );
      debit.addActionListener( this );
      buttonPanel.add( debit );
      zero = new Button( "Zero balances" );
      zero.addActionListener( this );
      buttonPanel.add( zero );
      done = new Button( "Done" );
      done.addActionListener( this );
      buttonPanel.add( done );
      recordDisplay = new TextArea( 4, 40 );

      // add the components to the Frame
      add( recordDisplay, BorderLayout.NORTH );
      add( buttonPanel, BorderLayout.SOUTH );

      setVisible( true );
   }

   public void actionPerformed( ActionEvent e )
   {
      if ( e.getSource() != done ) {
         accountType = e.getActionCommand();
         readRecords();
      }
      else {      // Close the file
         try {
            input.close();
            System.exit( 0 );
         }
         catch ( IOException ioe ) {
            System.err.println( "File not closed properly\n" +
                                ioe.toString() );
            System.exit( 1 );
         }
      }
   }

   public void readRecords()
   {
      int account;
      String first, last;
      double balance;
      DecimalFormat twoDigits = new DecimalFormat( "0.00" );

      // input the values from the file
      try {      // to catch IOException

         try {   // to catch EOFException
            recordDisplay.setText( "The accounts are:\n" );

            while ( true ) {
               account = input.readInt();
               first = input.readUTF();
               last = input.readUTF();
               balance = input.readDouble();

               if ( shouldDisplay( balance ) )
                  recordDisplay.append( account + "\t" +
                     first + "\t" + last + "\t" +
                     twoDigits.format( balance ) + "\n" );
            }
         }
         catch ( EOFException eof ) {
            input.seek( 0 );
         }
      }
      catch ( IOException e ) {
         System.err.println( "Error during read from file\n" +
                             e.toString() );
         System.exit( 1 );
      }
   }

   public boolean shouldDisplay( double balance )
   {
      if ( accountType.equals( "Credit balances" ) &&
           balance < 0 )
         return true;

      else if ( accountType.equals( "Debit balances" ) &&
                balance > 0 )
         return true;

      else if ( accountType.equals( "Zero balances" ) &&
                balance == 0 )
         return true;

      return false;
   }

   // Instantiate a CreditInquiry object and start the program
   public static void main( String args[] )
   {
      new CreditInquiry();
   }
}