Car Reservation Application

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

public class CarReservation extends JFrame
{
   // JLabel and JSpinner to display date
   private JLabel selectDateJLabel;
   private JSpinner dateJSpinner;

   // JLabel and JTextField to display name
   private JLabel nameJLabel;
   private JTextField nameJTextField;

   // JButton to reserve car
   private JButton reserveCarJButton;

   // BufferedReader and PrintWriter to allow 
   // reading from, and writing to, a file 
   private BufferedReader input; 
   private PrintWriter output; 
   
   // no-argument constructor
   public CarReservation()
   {
      createUserInterface();
   }

   // create and position GUI components
   public void createUserInterface()
   {
      // get content pane for attaching GUI components
      Container contentPane = getContentPane();
      
      // enable explicit positioning of GUI components
      contentPane.setLayout( null );
      
      // set up selectDateJLabel
      selectDateJLabel = new JLabel();
      selectDateJLabel.setBounds( 16, 16, 96, 23 );
      selectDateJLabel.setText( "Select the date:" );
      contentPane.add( selectDateJLabel );

      // set up dateJSpinner
      dateJSpinner = new JSpinner( new SpinnerDateModel() );
      dateJSpinner.setBounds( 16, 43, 250, 23 );
      dateJSpinner.setEditor( new JSpinner.DateEditor( 
         dateJSpinner, "MM/dd/yyyy" ) ); 
      contentPane.add( dateJSpinner );
      dateJSpinner.addChangeListener(
      
         new ChangeListener() // anonymous inner class
         {
            // event handler called when dateJSpinner is changed
            public void stateChanged( ChangeEvent event )
            {
               dateJSpinnerChanged( event );
            }
            
         } // end anonymous inner class
         
      ); // end call to addActionListener            
            
      // set up nameJLabel
      nameJLabel = new JLabel();
      nameJLabel.setBounds( 16, 70, 100, 23 );
      nameJLabel.setText( "Name: " );
      contentPane.add( nameJLabel );
            
      // set up nameJTextField
      nameJTextField = new JTextField();
      nameJTextField.setBounds( 16, 97, 250, 23 );
      contentPane.add( nameJTextField );
      
      // set up reserveCarJButton
      reserveCarJButton = new JButton();
      reserveCarJButton.setBounds( 16, 130, 250, 23 );
      reserveCarJButton.setText( "Reserve Car" );
      contentPane.add( reserveCarJButton );
      reserveCarJButton.addActionListener(

         new ActionListener() // anonymous inner class
         {
            // event handler called when reserveCarJButton is clicked
            public void actionPerformed( ActionEvent event )
            {
               reserveCarJButtonActionPerformed( event );
            }

         } // end anonymous inner class

      ); // end call to addActionListener
            
      // set properties of application's window
      setTitle( "Car Reservation" ); // set title bar string
      setSize( 287, 190 );           // set window size
      setVisible( true );            // display window

   } // end method createUserInterface
   
   // write reservation to a file
   private void reserveCarJButtonActionPerformed( ActionEvent event )
   {
	  File reserveFile = new File( "reservations.txt" ); 
	  
	  // read reservations from, and write a reservation to, a file
	  try
	  {
		  // create buffered read to open and read text file
		  FileReader inputFile = new FileReader ( reserveFile );
		  input = new BufferedReader( inputFile ); 
		  
		  // get selected date
		  Date fullDate = ( Date ) dateJSpinner.getValue();
		  String currentDate = fullDate.toString();
		  String monthDay = currentDate.substring( 0, 10 );
		  String year = currentDate.substring( 24, 28 ); 
		  currentDate = monthDay + " " + year; 
		  
		  int dateCount = 1;
		  String contents = input.readLine(); 
		  
		  // check if too many cars are reserved
		  while ( contents != null ) 
		  { 
			  // check reservation date
			  if ( contents.equals( currentDate ) ) 
			  { 
				  //check reservation number
				  if ( dateCount < 4 ) 
				  {
					  dateCount++; 
				  }
				  else
				  {
					  JOptionPane.showMessageDialog( this, "Too many " + 
						  "cars have already been reserved for that day.",
						  "Sorry", JOptionPane.INFORMATION_MESSAGE );
			
					  // disable reserveCarJbutton
					  reserveCarJButton.setEnabled( false );
				  
					  return; // exit method 
				  }
			  
			  } // end if
		  
			  contents = input.readLine(); // read next line
		  
		  } // end while 
	  
		  input.close(); // close BufferedReader 
	  
		  // creat PrintWriter to open and write text file 
		  FileWriter outputFile = new FileWriter( reserveFile, true );
		  output = new PrintWriter( outputFile ); 
	  
		  // write user input to file 
		  output.println( currentDate );
		  output.println( nameJTextField.getText() ); 
	  
		  JOptionPane.showMessageDialog( this, 
			  "Your car has been reserved.", "Thank you", 
			  JOptionPane.INFORMATION_MESSAGE );
		  
		  output.close(); // close PrintWriter
	  
	  } // end try 
	  catch ( IOException exception ) 
	  {
		  JOptionPane.showMessageDialog( this, "Invalid file.",
			  "Error", JOptionPane.ERROR_MESSAGE ); 
			  
		  // disable dateJSpinner and reserveCarJButton
		  dateJSpinner.setEnabled( false );
		  reserveCarJButton.setEnabled( false ); 
	  }
	  
	  nameJTextField.setText( "" );
						 
   } // end method reserveCarJButtonActionPerformed

   // enable reserveCarJButton
   private void dateJSpinnerChanged( ChangeEvent event )
   {
      reserveCarJButton.setEnabled( true );
   
   } // end method dateJSpinnerChanged
   
   // main method
   public static void main( String[] args )
   {
      CarReservation application = new CarReservation();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

   } // end method main

} // end class CarReservation

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stuck on this programming, not sure what im missing and i also have no error when i run the command prompt. however, when i the run the application, i get error invalid file, i should of got that say Your car has been reserved. Image im talking about