OOD Java Design Simplication

public class CourseGrades
{
   // Constant for the number of grades
   public final int NUM_GRADES = 4;
   
   // Variable to reference a GradedActivity
   // array
   private GradedActivity[] grades;
   
   /**
      Constructor
   */
      
   public CourseGrades()
   {
      // Create the grades array.
      grades = new GradedActivity[NUM_GRADES];
   }
   
   /**
      The setLab method stores a GradedActivity object
      for the lab grade.
      @param aLab Represents the lab grade.
   */
   
   public void setLab(GradedActivity aLab)
   {
      grades[0] = aLab;
   }
   
   /**
      The setPassFailExam method stores a PassFailExam object
      for the pass/fail exam grade.
      @param aPassFailExam Represents the pass/fail exam grade.
   */
   
   public void setPassFailExam(PassFailExam aPassFailExam)
   {
      grades[1] = aPassFailExam;
   }
 
   /**
      The setEssay method stores an Essay object
      for the essay grade.
      @param anEsay Represents the essay grade.
   */
      
   public void setEssay(Essay anEssay)
   {
      grades[2] = anEssay;
   }
 
   /**
      The setFinalExam method stores a FinalExam object
      for the final exam grade.
      @param aFinalExam Represents the final exam grade.
   */
   
   public void setFinalExam(FinalExam aFinalExam)
   {
      grades[3] = aFinalExam;
   }
 
   /**
      The toString method returns a string representation
      of the object.
      @return A string representation of the object.
   */
   
   public String toString()
   {
      String str = "Lab Score: " + grades[0].getScore() +
                   "\tGrade: " + grades[0].getGrade() +
                   "\nPass/Fail Exam Score: " + grades[1].getScore() +
                   "\tGrade: " + grades[1].getGrade() +
                   "\nEssay Score: " + grades[2].getScore() +
                   "\tGrade: " + grades[2].getGrade() +
                   "\nFinal Exam Score: " + grades[3].getScore() +
                   "\tGrade: " + grades[3].getGrade();
      
      return str;
   }
}
 
public class GradedActivity
{
   private double score;  // Numeric score
 
   /**
      The setScore method sets the score field.
      @param s The value to store in score.
   */
 
   public void setScore(double s)
   {
      score = s;
   }
 
   /**
      The getScore method returns the score.
      @return The value stored in the score field.
   */
 
   public double getScore()
   {
      return score;
   }
 
   /**
      The getGrade method returns a letter grade
      determined from the score field.
      @return The letter grade.
   */
 
   public char getGrade()
   {
      char letterGrade;
 
      if (score >= 90)
         letterGrade = 'A';
      else if (score >= 80)
         letterGrade = 'B';
      else if (score >= 70)
         letterGrade = 'C';
      else if (score >= 60)
         letterGrade = 'D';
      else
         letterGrade = 'F';
 
      return letterGrade;
   }
}
public class Essay extends GradedActivity
{
   private double grammar;				// Points for grammar
   private double spelling;			// Points for spelling
   private double correctLength;		// Points for length	
   private double content;				// Points for content
 
   /**
   	The setScore method sets points for grammar,
		spelling, length, and content.
		This method overloads the base class method.
		Note that the other "set" methods are
		private. Those methods are for validating
		points before they are assigned.
		@param gr Grammar points.
		@param sp Spelling points.
		@param len Length points.
		@param cnt Content points.
   */
 
   public void setScore(double gr, double sp, double len, double cnt)
   {
		// Set the individual scores.
		setGrammar(gr);
		setSpelling(sp);
		setCorrectLength(len);
		setContent(cnt);
		
		// Set the total score.
		super.setScore(grammar + spelling + correctLength + content);
	}
 
   /**
   	The setGrammar method sets the  grammar
		points, validating them before they are set.
		@param g Grammar points.
   */
 
   private void setGrammar(double g)
   {
		if (g <= 30.0)
      	grammar = g;
		else						// Invalid points
			grammar = 0.0;
   }
 
   /**
   	The setSpelling method sets the spelling
		points, validating them before they are set.
		@param s Spelling points.
   */
	
   private void setSpelling(double s)
   {
		if (s <= 20.0)
      	spelling = s;
		else						// Invalid points
			spelling = 0.0;
   }
 
   /**
   	The setCorrectLength method sets the points
		for correct length, validating them before
		they are set.
		@param c Correct length points.
   */
	
   private void setCorrectLength(double c)
   {
		if (c <= 20.0)
      	correctLength = c;
		else						// Invalid points
			correctLength = 0.0;
   }
 
   /**
   	The setContent method sets the points
		for content, validating them before
		they are set.
		@param c Content points.
   */
	
   private void setContent(double c)
   {
		if (c <= 30)
      	content = c;
		else						// Invalid points
			content = 0.0;
   }
 
   /**
   	The getGrammar method returns the points
		awarded for grammar.
		@return Gramar points.
   */
 
   public double getGrammar()
   {
      return grammar;
   }
 
   /**
   	The getSpelling method returns the points
		awarded for spelling.
		@return Spelling points.
   */
 
   public double getSpelling()
   {
      return spelling;
   }
 
   /**
   	The getCorrectLength method returns the points
		awarded for correct length.
		@return Correct length points.
   */
 
   public double getCorrectLength()
   {
      return correctLength;
   }
 
   /**
   	The getContent method returns the points
		awarded for content.
		@return Content points.
   */
	
   public double getContent()
   {
      return content;
   }
 
   /**
   	The getScore method returns the overall
		numeric score. Overrides the base class
		method.
		@return Overall numeric score.
   */
 
   public double getScore()
   {
      return grammar + spelling + correctLength + content;
   }
}
/**
   This class determines the grade for a final exam.
*/
 
public class FinalExam extends GradedActivity
{
   private int numQuestions;  // Number of questions
   private double pointsEach; // Points for each question
   private int numMissed;     // Questions missed
 
   /**
      The constructor sets the number of questions on the
      exam and the number of questions missed.
      @param questions The number of questions.
      @param missed The number of questions missed.
   */
 
   public FinalExam(int questions, int missed)
   {
      double numericScore;  // To hold a numeric score
 
      // Set the numQuestions and numMissed fields.
      numQuestions = questions;
      numMissed = missed;
 
      // Calculate the points for each question and
      // the numeric score for this exam.
      pointsEach = 100.0 / questions;
      numericScore = 100.0 - (missed * pointsEach);
 
      // Call the inherited setScore method to
      // set the numeric score.
      setScore(numericScore);
   }
 
   /**
      The getPointsEach method returns the number of
      points each question is worth.
      @return The value in the pointsEach field.
   */
 
   public double getPointsEach()
   {
      return pointsEach;
   }
 
   /**
      The getNumMissed method returns the number of 
      questions missed.
      @return The value in the numMissed field.
   */
 
   public int getNumMissed()
   {
      return numMissed;
   }
}
 
public class PassFailActivity extends GradedActivity
{
   private double minPassingScore; // Minimum passing score
 
   /**
      The constructor sets the minimum passing score.
      @param mps The minimum passing score.
   */
 
   public PassFailActivity(double mps)
   {
      minPassingScore = mps;
   }
 
   /**
      The getGrade method returns a letter grade
      determined from the score field. This
      method overrides the superclass method.
      @return The letter grade.
   */
 
   public char getGrade()
   {
      char letterGrade;
 
      if (super.getScore() >= minPassingScore)
         letterGrade = 'P';
      else
         letterGrade = 'F';
 
      return letterGrade;
   }
}
public class PassFailExam extends PassFailActivity
{
   private int numQuestions;  // Number of questions
   private double pointsEach; // Points for each question
   private int numMissed;     // Number of questions missed
 
   /**
      The constructor sets the number of questions, the
      number of questions missed, and the minimum passing
      score.
      @param questions The number of questions.
      @param missed The number of questions missed.
      @param minPassing The minimum passing score.
   */
 
   public PassFailExam(int questions, int missed, 
               double minPassing)
   {
      // Call the superclass constructor.
      super(minPassing);
 
      // Declare a local variable for the score.
      double numericScore;
 
      // Set the numQuestions and numMissed fields.
      numQuestions = questions;
      numMissed = missed;
 
      // Calculate the points for each question and
      // the numeric score for this exam.
      pointsEach = 100.0 / questions;
      numericScore = 100.0 - (missed * pointsEach);
 
      // Call the superclass's setScore method to
      // set the numeric score.
      setScore(numericScore);
   }
 
   /**
      The getPointsEach method returns the number of
      points each question is worth.
      @return The value in the pointsEach field.
   */
 
   public double getPointsEach()
   {
      return pointsEach;
   }
 
   /**
      The getNumMissed method returns the number of 
      questions missed.
      @return The value in the numMissed field.
   */
 
   public int getNumMissed()
   {
      return numMissed;
   }
}