Applet Event Handler

Question

Would someone please help me. I am new to applet development and I get a compile error associated with the event handling in my first ever applet code as follows:
C:\j2sdk1.4.2_01\bin>javac trajectory_j.java
trajectory_j.java:248: illegal start of expression
private class Handler implements ActionListener {
^
trajectory_j.java:248: ';' expected
private class Handler implements ActionListener {
^
2 errors
de.
This is the code:
// trajectory Analysis Program: trajectory_j.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class trajectory_j extends JApplet implements ActionListener {
     private JTextArea introductionArea, resultsArea;
     private JLabel spanLabel, chordLabel,
          thicknessLabel, massLabel, altitudeLabel, velocityLabel,
          trajectory_angleLabel, time_incrementLabel, rotation_factorLabel,
          calculationLabel, resultsLabel;
     private JTextField spanField, chordField, thicknessField,
          massField, altitudeField, velocityField, trajectory_angleField,
          time_incrementField, rotation_factorField;
     private JButton startButton, resetButton, contButton, termButton;
     String introduction_string, span_string, chord_string, thickness_string, mass_string,
          altitude_string, velocity_string, trajectory_angle_string,
          time_increment_string, rotation_factor_string, results_string;
     double span, chord, thickness, mass, altitude, velocity, trajectory_angle, time_increment,
          rotation_factor, distance, velocity_fps, elapsed_time;
     int status_a;
     int status_b;
     int status_c;
/* deletion of code segment a
          span = 0;
          chord = 0;
          thickness = 0;
          mass = 0;
          altitude = 0;
          velocity = 0;
          trajectory_angle = 0;
          time_increment = 0;
          rotation_factor = 0;
          distance = 0;
          velocity_fps = 0;
          elapsed_time = 0;
          velocity_fps = 0;
          elapsed_time = 0;
     // create objects
     public void init()
          status_a = 0;
          status_b = 0;
          status_c = 0;
          // create container & panel
          Container container = getContentPane();     
          Panel panel = new Panel( new FlowLayout( FlowLayout.LEFT));
          container.add( panel );
          // set up vertical boxlayout
          Box box = Box.createVerticalBox();
          Box inputbox1 = Box.createHorizontalBox();
          Box inputbox2 = Box.createHorizontalBox();
          Box inputbox3 = Box.createHorizontalBox();
          Box buttonbox = Box.createHorizontalBox();
          introduction_string = "This is the introduction";
          // set up introduction
          introductionArea = new JTextArea( introduction_string, 10, 50 );
          introductionArea.setEditable( false );
          box.add( new JScrollPane( introductionArea ) );
          box.add( Box.createVerticalStrut (10) );
          box.add( inputbox1);
          // set up span
          spanLabel = new JLabel( "span (feet)" );
          spanField = new JTextField(5 );
          inputbox1.add( spanLabel );
          inputbox1.add( spanField );
          Dimension minSize = new Dimension(5, 15);
          Dimension prefSize = new Dimension(5, 15);
          Dimension maxSize = new Dimension(Short.MAX_VALUE, 15);
          inputbox1.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up chord
          chordLabel = new JLabel( "chord (feet)" );
          chordField = new JTextField(5 );
          inputbox1.add( chordLabel );
          inputbox1.add( chordField );
          inputbox1.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up thickness
          thicknessLabel = new JLabel( "thickness (feet)" );
          thicknessField = new JTextField(5 );
          inputbox1.add( thicknessLabel );
          inputbox1.add( thicknessField );
          inputbox1.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up mass
          massLabel = new JLabel( "mass (slugs)" );
          massField = new JTextField(5);
          inputbox1.add( massLabel );
          inputbox1.add( massField );
          box.add( Box.createVerticalStrut (10) );
          box.add( inputbox2);
          // set up altitude
          altitudeLabel = new JLabel( "altitude (feet)");
          altitudeField = new JTextField(5 );
          inputbox2.add( altitudeLabel );
          inputbox2.add( altitudeField );
          inputbox2.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up velocity
          velocityLabel = new JLabel( "velocity (Mach Number)");
          velocityField = new JTextField(5);
          inputbox2.add( velocityLabel );
          inputbox2.add( velocityField );
          inputbox2.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up trajectory_angle
          trajectory_angleLabel = new JLabel( "trajectory angle ( -90 degrees <= trajectory angle <= 90 degrees )");
          trajectory_angleField = new JTextField(5);
          inputbox2.add( trajectory_angleLabel );
          inputbox2.add( trajectory_angleField );
          box.add( Box.createVerticalStrut (10) );
          box.add( inputbox3);
          Dimension minSizeF = new Dimension(70, 15);
          Dimension prefSizeF = new Dimension(70, 15);
          Dimension maxSizeF = new Dimension(Short.MAX_VALUE, 15);
          inputbox3.add(new Box.Filler(minSizeF, prefSizeF, maxSizeF));
          // set up time_increment
          time_incrementLabel = new JLabel( "time increment (seconds)" );
          time_incrementField = new JTextField(5);
          inputbox3.add( time_incrementLabel );
          inputbox3.add( time_incrementField );
          inputbox3.add(new Box.Filler(minSizeF, prefSizeF, maxSizeF));
          // set up rotation_factor
          rotation_factorLabel = new JLabel( "rotation factor ( non-negative number)" );
          rotation_factorField = new JTextField(5);
          inputbox3.add( rotation_factorLabel );
          inputbox3.add( rotation_factorField );
          inputbox3.add(new Box.Filler(minSizeF, prefSizeF, maxSizeF));
          box.add( Box.createVerticalStrut (10) );
          box.add( buttonbox);
          // set up start
          startButton = new JButton( "START" );
          buttonbox.add( startButton );
          Dimension minSizeB = new Dimension(10, 30);
          Dimension prefSizeB = new Dimension(10, 30);
          Dimension maxSizeB = new Dimension(Short.MAX_VALUE, 30);
          buttonbox.add(new Box.Filler(minSizeB, prefSizeB, maxSizeB));
          // set up reset
          resetButton = new JButton( "RESET" );
          buttonbox.add( resetButton );
          buttonbox.add(new Box.Filler(minSizeB, prefSizeB, maxSizeB));
          // set up cont
          contButton = new JButton( "CONTINUE" );
          buttonbox.add( contButton );
          buttonbox.add(new Box.Filler(minSizeB, prefSizeB, maxSizeB));
          // set up term
          termButton = new JButton( "END" );
          buttonbox.add( termButton );
          box.add( Box.createVerticalStrut (10) );          
          // set up results
          resultsArea = new JTextArea( results_string, 10, 50 );
          resultsArea.setEditable( false );
          box.add( new JScrollPane( resultsArea ) );
          // add box to panel
          panel.add( box );
          // register event handlers
          Handler handler = new Handler();
          spanField.addActionListener( handler );
          chordField.addActionListener( handler );          
          thicknessField.addActionListener( handler );
          massField.addActionListener( handler );
          altitudeField.addActionListener( handler );
          velocityField.addActionListener( handler );          
          trajectory_angleField.addActionListener( handler );
          time_incrementField.addActionListener( handler );
          rotation_factorField.addActionListener( handler );
          startButton.addActionListener( handler );
          resetButton.addActionListener( handler );
          contButton.addActionListener( handler );
          termButton.addActionListener( handler );
// private inner class for event handling
private class Handler implements ActionListener {
     // process handler events
     public void actionPerformed( ActionEvent event )
          // process resetButton event
          if ( event.getSource() == resetButton )
               reset();
          // process contButton event
          if ( event.getSource() == contButton )
               cont();
          // process endButton event
          if ( event.getSource() == termButton )
          // process span event
          if( event.getSource() == spanField ) {
               span = Double.parseDouble( event.getActionCommand() );
               spanField.setText( span_string );
               status_b++;
          // process chord event
          if( event.getSource() == spanField ) {
               span = Double.parseDouble( event.getActionCommand() );
               spanField.setText( chord_string );
               status_b++;     
          // process thickness event
          if( event.getSource() == thicknessField ) {
               thickness = Double.parseDouble( event.getActionCommand() );
               spanField.setText( thickness_string );     
               status_b++;
          // process mass event
          if( event.getSource() == massField ) {
               mass = Double.parseDouble( event.getActionCommand() );
               spanField.setText( mass_string );
               status_b++;     
          // process altitude event
          if( event.getSource() == altitudeField ) {
               altitude = Double.parseDouble( event.getActionCommand() );
               spanField.setText( altitude_string );     
               status_b++;
          // process velocity event
          if( event.getSource() == velocityField ) {
               velocity = Double.parseDouble( event.getActionCommand() );
               spanField.setText( velocity_string );
               status_b++;
          // process trajectory_angle event
          if( event.getSource() == trajectory_angleField ) {
               trajectory_angle = Double.parseDouble( event.getActionCommand() );
               spanField.setText( trajectory_angle_string );
               status_b++;
          // process time_increment event
          if( event.getSource() == time_incrementField ) {
               time_increment = Double.parseDouble( event.getActionCommand() );
               spanField.setText( time_increment_string );
               status_b++;
          // process rotation_factor event
          if( event.getSource() == rotation_factorField ) {
               rotation_factor = Double.parseDouble( event.getActionCommand() );
               spanField.setText( rotation_factor_string );
               status_b++;
          // process startButton event
          if ( event.getSource() == startButton && status_b == 9 ) {
               status_c = 1;
     } // end method event handler
} // end Handler class
     } // end method init
     public void strtb()
/* deletion of code segment 1
          startButton.addActionListener(
               new ActionListener() {  // anonymous inner class
                    // set text in resultsArea
                    public void actionPerformed( ActionEvent event )
                    if( status_c == 1 ){
                    calculate();
                    results();
                    resultsArea.setText( results() );
/* deletion of code segment 2                    
                    }// end method actionPerformed1
               } // end anonymous inner class1
          ); // end call to addActionlistener1
     } // end method strtb
     public void reset()
/* deletion of code segment 3
          resetButton.addActionListener(
               new ActionListener() {  // anonymous inner class
                    // set text in resultsArea
                    public void actionPerformed( ActionEvent event )
                    span_string = "";
                    chord_string = "";
                    thickness_string = "";
                    mass_string = "";
                    altitude_string = "";
                    velocity_string = "";
                    trajectory_angle_string = "";
                    time_increment_string = "";
                    rotation_factor_string = "";
                    results_string = "";
                    spanField.setText( span_string );
                    chordField.setText( chord_string );
                    thicknessField.setText( thickness_string );
                    massField.setText( mass_string );
                    altitudeField.setText( altitude_string );
                    velocityField.setText( velocity_string );
                    trajectory_angleField.setText( trajectory_angle_string );
                    time_incrementField.setText( time_increment_string );
                    rotation_factorField.setText( rotation_factor_string );
resultsArea.setEditable( true );
                    resultsArea.setText( results_string );
resultsArea.setEditable( false );
                    span = 0;
                    chord = 0;
                    thickness = 0;
                    mass = 0;
                    altitude = 0;
                    velocity = 0;
                    trajectory_angle = 0;
                    time_increment = 0;
                    rotation_factor = 0;
                    distance = 0;
                    velocity_fps = 0;
                    elapsed_time = 0;
/* deletion of code segment 4               
                    } // end method actionPerformed2
               } // end anonymous inner class2
          ); // end call to addActionlistener2
     } // end method reset
     public void cont()
     //later
     public void calculate()
     distance = 1;
     altitude = 2;
     trajectory_angle = 3;
     velocity_fps = 4;
     elapsed_time = 5;
     public String results()
     results_string =
     "Distance =\t\t" + distance + " miles\n"
     + "Altitude =\t\t" + altitude + " feet\n"
     + "Trajectory Angle =\t" + trajectory_angle + " degrees\n"
     + "Velocity =\t\t" + velocity_fps + " feet per second\n"
     + "Elapsed Time =\t\t" + elapsed_time + " seconds\n"
     + "\nstatus_a = " + status_a + "\nstatus_b = "
     + status_b + "\nstatus_c = " + status_c;
     return results_string;
public void start()
if(status_a == 0 )
strtb();
if (status_b == 0)
reset();
}// end method start
} //end class trajectory_a

Answer 1

The following are copies of html and java source code files for a prior runnable version ( trajectory_b ) of this program which can enlighten some functionality intended by the program.
(trajectory_b.html):
<html>
<appletcode = "trajectory_b.class" width = "800" height = "600">
</applet>
</html>
(trajectory_b.java):
// trajectory Analysis Program: trajectory_b.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class trajectory_b extends JApplet implements ActionListener {
     private JTextArea introductionArea, resultsArea;
     private JLabel spanLabel, chordLabel,
          thicknessLabel, massLabel, altitudeLabel, velocityLabel,
          trajectory_angleLabel, time_incrementLabel, rotation_factorLabel,
          calculationLabel, resultsLabel;
     private JTextField spanField, chordField, thicknessField,
          massField, altitudeField, velocityField, trajectory_angleField,
          time_incrementField, rotation_factorField;
     private JButton startButton, resetButton, contButton, termButton;
     String introduction_string, span_string, chord_string, thickness_string, mass_string,
          altitude_string, velocity_string, trajectory_angle_string,
          time_increment_string, rotation_factor_string, results_string;
     double span, chord, thickness, mass, altitude, velocity, trajectory_angle, time_increment,
          rotation_factor, distance, velocity_fps, elapsed_time;
     int status_a;
     int status_b;
     int status_c;
/* deletion of code segment a
          span = 0;
          chord = 0;
          thickness = 0;
          mass = 0;
          altitude = 0;
          velocity = 0;
          trajectory_angle = 0;
          time_increment = 0;
          rotation_factor = 0;
          distance = 0;
          velocity_fps = 0;
          elapsed_time = 0;
          velocity_fps = 0;
          elapsed_time = 0;
     // create objects
     public void init()
          status_a = 0;
          status_b = 0;
          status_c = 0;
          // create container & panel
          Container container = getContentPane();     
          Panel panel = new Panel( new FlowLayout( FlowLayout.LEFT));
          container.add( panel );
          // set up vertical boxlayout
          Box box = Box.createVerticalBox();
          Box inputbox1 = Box.createHorizontalBox();
          Box inputbox2 = Box.createHorizontalBox();
          Box inputbox3 = Box.createHorizontalBox();
          Box buttonbox = Box.createHorizontalBox();
          introduction_string = "This is the introduction";
          // set up introduction
          introductionArea = new JTextArea( introduction_string, 10, 50 );
          introductionArea.setEditable( false );
          box.add( new JScrollPane( introductionArea ) );
          box.add( Box.createVerticalStrut (10) );
          box.add( inputbox1);
          // set up span
          spanLabel = new JLabel( "span (feet)" );
          spanField = new JTextField(5 );
          inputbox1.add( spanLabel );
          inputbox1.add( spanField );
          Dimension minSize = new Dimension(5, 15);
          Dimension prefSize = new Dimension(5, 15);
          Dimension maxSize = new Dimension(Short.MAX_VALUE, 15);
          inputbox1.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up chord
          chordLabel = new JLabel( "chord (feet)" );
          chordField = new JTextField(5 );
          inputbox1.add( chordLabel );
          inputbox1.add( chordField );
          inputbox1.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up thickness
          thicknessLabel = new JLabel( "thickness (feet)" );
          thicknessField = new JTextField(5 );
          inputbox1.add( thicknessLabel );
          inputbox1.add( thicknessField );
          inputbox1.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up mass
          massLabel = new JLabel( "mass (slugs)" );
          massField = new JTextField(5);
          inputbox1.add( massLabel );
          inputbox1.add( massField );
          box.add( Box.createVerticalStrut (10) );
          box.add( inputbox2);
          // set up altitude
          altitudeLabel = new JLabel( "altitude (feet)");
          altitudeField = new JTextField(5 );
          inputbox2.add( altitudeLabel );
          inputbox2.add( altitudeField );
          inputbox2.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up velocity
          velocityLabel = new JLabel( "velocity (Mach Number)");
          velocityField = new JTextField(5);
          inputbox2.add( velocityLabel );
          inputbox2.add( velocityField );
          inputbox2.add(new Box.Filler(minSize, prefSize, maxSize));
          // set up trajectory_angle
          trajectory_angleLabel = new JLabel( "trajectory angle ( -90 degrees <= trajectory angle <= 90 degrees )");
          trajectory_angleField = new JTextField(5);
          inputbox2.add( trajectory_angleLabel );
          inputbox2.add( trajectory_angleField );
          box.add( Box.createVerticalStrut (10) );
          box.add( inputbox3);
          Dimension minSizeF = new Dimension(70, 15);
          Dimension prefSizeF = new Dimension(70, 15);
          Dimension maxSizeF = new Dimension(Short.MAX_VALUE, 15);
          inputbox3.add(new Box.Filler(minSizeF, prefSizeF, maxSizeF));
          // set up time_increment
          time_incrementLabel = new JLabel( "time increment (seconds)" );
          time_incrementField = new JTextField(5);
          inputbox3.add( time_incrementLabel );
          inputbox3.add( time_incrementField );
          inputbox3.add(new Box.Filler(minSizeF, prefSizeF, maxSizeF));
          // set up rotation_factor
          rotation_factorLabel = new JLabel( "rotation factor ( non-negative number)" );
          rotation_factorField = new JTextField(5);
          inputbox3.add( rotation_factorLabel );
          inputbox3.add( rotation_factorField );
          inputbox3.add(new Box.Filler(minSizeF, prefSizeF, maxSizeF));
          box.add( Box.createVerticalStrut (10) );
          box.add( buttonbox);
          // set up start
          startButton = new JButton( "START" );
          buttonbox.add( startButton );
          Dimension minSizeB = new Dimension(10, 30);
          Dimension prefSizeB = new Dimension(10, 30);
          Dimension maxSizeB = new Dimension(Short.MAX_VALUE, 30);
          buttonbox.add(new Box.Filler(minSizeB, prefSizeB, maxSizeB));
          // set up reset
          resetButton = new JButton( "RESET" );
          buttonbox.add( resetButton );
          buttonbox.add(new Box.Filler(minSizeB, prefSizeB, maxSizeB));
          // set up cont
          contButton = new JButton( "CONTINUE" );
          buttonbox.add( contButton );
          buttonbox.add(new Box.Filler(minSizeB, prefSizeB, maxSizeB));
          // set up term
          termButton = new JButton( "END" );
          buttonbox.add( termButton );
          box.add( Box.createVerticalStrut (10) );          
          // set up results
          resultsArea = new JTextArea( results_string, 10, 50 );
          resultsArea.setEditable( false );
          box.add( new JScrollPane( resultsArea ) );
          // add box to panel
          panel.add( box );
          // register event handlers
          Handler handler = new Handler();
          spanField.addActionListener( handler );
          chordField.addActionListener( handler );          
          thicknessField.addActionListener( handler );
          massField.addActionListener( handler );
          altitudeField.addActionListener( handler );
          velocityField.addActionListener( handler );          
          trajectory_angleField.addActionListener( handler );
          time_incrementField.addActionListener( handler );
          rotation_factorField.addActionListener( handler );
          startButton.addActionListener( handler );
          resetButton.addActionListener( handler );
          contButton.addActionListener( handler );
          termButton.addActionListener( handler );
} // end method init
     // process handler events
     public void actionPerformed( ActionEvent event )
          // process resetButton event
          if ( event.getSource() == resetButton )
               reset();
          // process contButton event
          if ( event.getSource() == contButton )
               cont();
          // process endButton event
          if ( event.getSource() == termButton )
          // process span event
          if( event.getSource() == spanField ) {
               span = Double.parseDouble( event.getActionCommand() );
               spanField.setText( span_string );
               status_b++;
          // process chord event
          if( event.getSource() == spanField ) {
               span = Double.parseDouble( event.getActionCommand() );
               spanField.setText( chord_string );
               status_b++;     
          // process thickness event
          if( event.getSource() == thicknessField ) {
               thickness = Double.parseDouble( event.getActionCommand() );
               spanField.setText( thickness_string );     
               status_b++;
          // process mass event
          if( event.getSource() == massField ) {
               mass = Double.parseDouble( event.getActionCommand() );
               spanField.setText( mass_string );
               status_b++;     
          // process altitude event
          if( event.getSource() == altitudeField ) {
               altitude = Double.parseDouble( event.getActionCommand() );
               spanField.setText( altitude_string );     
               status_b++;
          // process velocity event
          if( event.getSource() == velocityField ) {
               velocity = Double.parseDouble( event.getActionCommand() );
               spanField.setText( velocity_string );
               status_b++;
          // process trajectory_angle event
          if( event.getSource() == trajectory_angleField ) {
               trajectory_angle = Double.parseDouble( event.getActionCommand() );
               spanField.setText( trajectory_angle_string );
               status_b++;
          // process time_increment event
          if( event.getSource() == time_incrementField ) {
               time_increment = Double.parseDouble( event.getActionCommand() );
               spanField.setText( time_increment_string );
               status_b++;
          // process rotation_factor event
          if( event.getSource() == rotation_factorField ) {
               rotation_factor = Double.parseDouble( event.getActionCommand() );
               spanField.setText( rotation_factor_string );
               status_b++;
          // process startButton event
          if ( event.getSource() == startButton && status_b == 9 ) {
               strtb();
     } // end method event handler
     public void strtb()
          startButton.addActionListener(
               new ActionListener() {  // anonymous inner class
                    // set text in resultsArea
                    public void actionPerformed( ActionEvent event )
                    calculate();
                    results();
                    resultsArea.setText( results() );
                    }// end method actionPerformed1
               } // end anonymous inner class1
          ); // end call to addActionlistener1
     } // end method strtb
     public void reset()
          resetButton.addActionListener(
               new ActionListener() {  // anonymous inner class
                    // set text in resultsArea
                    public void actionPerformed( ActionEvent event )
                    span_string = "";
                    chord_string = "";
                    thickness_string = "";
                    mass_string = "";
                    altitude_string = "";
                    velocity_string = "";
                    trajectory_angle_string = "";
                    time_increment_string = "";
                    rotation_factor_string = "";
                    results_string = "";
                    spanField.setText( span_string );
                    chordField.setText( chord_string );
                    thicknessField.setText( thickness_string );
                    massField.setText( mass_string );
                    altitudeField.setText( altitude_string );
                    velocityField.setText( velocity_string );
                    trajectory_angleField.setText( trajectory_angle_string );
                    time_incrementField.setText( time_increment_string );
                    rotation_factorField.setText( rotation_factor_string );
resultsArea.setEditable( true );
                    resultsArea.setText( results_string );
resultsArea.setEditable( false );
                    span = 0;
                    chord = 0;
                    thickness = 0;
                    mass = 0;
                    altitude = 0;
                    velocity = 0;
                    trajectory_angle = 0;
                    time_increment = 0;
                    rotation_factor = 0;
                    distance = 0;
                    velocity_fps = 0;
                    elapsed_time = 0;
                    } // end method actionPerformed2
               } // end anonymous inner class2
          ); // end call to addActionlistener2
     } // end method reset
     public void cont()
     //later
     public void calculate()
     distance = 1;
     altitude = 2;
     trajectory_angle = 3;
     velocity_fps = 4;
     elapsed_time = 5;
     public String results()
     results_string =
     "Distance =\t\t" + distance + " miles\n"
     + "Altitude =\t\t" + altitude + " feet\n"
     + "Trajectory Angle =\t" + trajectory_angle + " degrees\n"
     + "Velocity =\t\t" + velocity_fps + " feet per second\n"
     + "Elapsed Time =\t\t" + elapsed_time + " seconds\n"
     + "\nstatus_a = " + status_a + "\nstatus_b = "
     + status_b + "\nstatus_c = " + status_c;
     return results_string;
public void start()
if(status_a == 0 )
strtb();
if (status_b == 0)
reset();
}// end method start
} //end class trajectory_b