readsequentialfile.java

用JAVA开发的交易处理程序

// Fig. 15.6: ReadSequentialFile.java
// This program reads a file sequentially and displays each
// record in text fields.
import java.io.*;
import java.awt.*;
import java.awt.event.*;

public class ReadSequentialFile extends Frame
             implements ActionListener {

   // TextFields to display account number, first name,
   // last name and balance.
   private TextField accountField, firstNameField,
                     lastNameField, balanceField;

   private Button next,   // get next record in file
                  done;   // quit program

   // Application other pieces
   private DataInputStream input;

   // Constructor -- initialize the Frame 
   public ReadSequentialFile()
   {
      super( "Read Client File" );

      // Open the file
      try {
         input = new DataInputStream(
                     new FileInputStream( "client.dat" ) );
      }
      catch ( IOException e ) {
         System.err.println( "File not opened properly\n" +
                             e.toString() );
         System.exit( 1 );
      }      

      setSize( 300, 150 );
      setLayout( new GridLayout( 5, 2 ) );

      // create the components of the Frame
      add( new Label( "Account Number" ) );
      accountField = new TextField();
      accountField.setEditable( false );
      add( accountField );

      add( new Label( "First Name" ) );
      firstNameField = new TextField( 20 );
      firstNameField.setEditable( false );
      add( firstNameField );      

      add( new Label( "Last Name" ) );
      lastNameField = new TextField( 20 );
      lastNameField.setEditable( false );
      add( lastNameField );

      add( new Label( "Balance" ) );
      balanceField = new TextField( 20 );
      balanceField.setEditable( false );
      add( balanceField );

      next = new Button( "Next" );
      next.addActionListener( this );
      add( next );      

      done = new Button( "Done" );
      done.addActionListener( this );
      add( done );       

      setVisible( true );  
   }

   public void actionPerformed( ActionEvent e )
   {
      if ( e.getSource() == next )
         readRecord();
      else
         closeFile();
   }

   public void readRecord()
   {
      int account;
      String first, last;
      double balance;

      // input the values from the file
      try {
         account = input.readInt();
         first = input.readUTF();
         last = input.readUTF();
         balance = input.readDouble();

         accountField.setText( String.valueOf( account ) );
         firstNameField.setText( first );
         lastNameField.setText( last );
         balanceField.setText( String.valueOf( balance ) );
      }
      catch ( EOFException eof ) {
         closeFile();
      }
      catch ( IOException e ) {
         System.err.println( "Error during read from file\n" +
                             e.toString() );
         System.exit( 1 );
      }
   }

   private void closeFile()
   {
      try {
         input.close();
         System.exit( 0 );
      }
      catch ( IOException e ) {
         System.err.println( "Error closing file\n" +
                             e.toString() );
         System.exit( 1 );
      }
   }

   public static void main( String args[] )
   {
      new ReadSequentialFile();
   }
}