// Fig. 6.16: FibonacciTest.java
// Recursive fibonacci method.
import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class FibonacciTest extends JApplet implements ActionListener {
   JLabel numberLabel, resultLabel;
   JTextField numberField, resultField;

   // set up applet’s GUI
   public void init()
   {
      // obtain content pane and set its layout to FlowLayout
      Container container = getContentPane();
      container.setLayout( new FlowLayout() );

      // create numberLabel and attach it to content pane
      numberLabel = new JLabel( "Enter an integer and press Enter" );
      container.add( numberLabel );

      // create numberField and attach it to content pane
      numberField = new JTextField( 10 );
      container.add( numberField );

      // register this applet as numberField’s ActionListener
      numberField.addActionListener( this );

      // create resultLabel and attach it to content pane
      resultLabel = new JLabel( "Fibonacci value is" );
      container.add( resultLabel );

      // create numberField, make it uneditable
      // and attach it to content pane
      resultField = new JTextField( 15 );
      resultField.setEditable( false );
      container.add( resultField );

   } // end method init

   // obtain user input and call method fibonacci
   public void actionPerformed( ActionEvent event )
   {  
      long number, fibonacciValue;

      // obtain user’s input and convert to long
      number = Long.parseLong( numberField.getText() );

      showStatus( "Calculating ..." ); 

      // calculate fibonacci value for number user input
      fibonacciValue = fibonacci( number );

      // indicate processing complete and display result
      showStatus( "Done." );   
      resultField.setText( Long.toString( fibonacciValue ) );

   } // end method actionPerformed
  
   // recursive declaration of method fibonacci
   public long fibonacci( long n )
   {
      // base case
      if ( n == 0 || n == 1 )  
         return n;

      // recursive step
      else
         return fibonacci( n - 1 ) + fibonacci( n - 2 );

   } // end method fibonacci

} // end class FibonacciTest


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