help in java Programming

Hi
Guys, I need your help I am trying to improve my java programming skills I find this question I am confident of my half way answer her is the question and her is my answer to it so far could you please help (this not a homework)

I need to design and implement a class called Course that represents a course taken at a school. A course object should keep track of up to five students, as represented by the modified Student class The constructor of the Course class should accept only the name of the course, provide a method called addStudent that accepts one Student parameter (the Course object should keep track of how many valid students have been added to the course). I need to provide a method called average that computes and returns the average of all students’ test score averages. I need to provide a method called roll that prints all students in the course. And a need to create a driver class with a main method that creates a course, and adds several students, prints a roll and prints the overall course test average.  

here is my code

public class Address
{
   private String streetAddress, city, state;
   private long zipCode;

   public Address (String street, String town, String st, long zip)
   {
      streetAddress = street;
      city = town;
      state = st;
      zipCode = zip;
   }

   
   public String toString()
   {
      String result;

      result = streetAddress + "\n";
      result += city + ", " + state + "  " + zipCode;

      return result;
   }
}

------------------------------------------------------------------------------------------
public class Grade
{
   private int grade1, grade2, grade3;
   private float average;

 
    public Grade (int gr1, int grade2, int grade3)
   {
      grade1 = gr1;
      this.grade2 = grade2;
      this.grade3 = grade3;

   }


   public void setTestScore ( int testNum, int newGrade)
   {
       switch (testNum) {
      case 1: grade1 = newGrade;
            break;
      case 2: grade2 = newGrade;
            break;
      case 3: grade3 = newGrade;
            break;
      default: System.out.println("Horrible ERROR!!!!");
      }
    }

    public int getTestScore(int testNum)
    {
     int testScore = -1;
---------------------------------------------------------------------------------------------------------------
public class Student
{
   private String firstName, lastName;
   private Address homeAddress, schoolAddress;
   private int grade1, grade2, grade3;
   private float average;

   
   public Student (String first, String last, Address home,
                   Address school)
   {
      firstName = first;
      lastName = last;
      homeAddress = home;
      schoolAddress = school;
      grade1 = 0;
      grade2 = 0;
      grade3 =0;
   }

   public Student (String first, String last, Address home, Address school, int gr1, int grade2, int grade3)
   {
      firstName = first;
      lastName = last;
      homeAddress = home;
      schoolAddress = school;
      grade1 = gr1;
      this.grade2 = grade2;
      this.grade3 = grade3;

   }


   public void setTestScore ( int testNum, int newGrade)
   {
-------------------------------------------------------------------------------------------------------------
public class StudentBody
{
 
   public static void main (String[] args)
   {
      Address school = new Address ("800 Lancaster Ave.", "Villanova",
                                    "PA", 19085);

      Address jHome = new Address ("21 Jump Street", "Lynchburg",
                                   "VA", 24551);
      Student john = new Student ("John", "Smith", jHome, school);


      Address mHome = new Address ("123 Main Street", "Euclid", "OH",
                                   44132);
      Student marsha = new Student ("Marsha", "Jones", mHome, school,75,87,98);
   
     

      System.out.println (john);
/*      System.out.println ();
      System.out.println (marsha);

      System.out.println( "\n\n\nMarsha's average: " + marsha.calcAverage());
marsha.setTestScore(2,50);
      System.out.println("Marsha's second test score : " + marsha.getTestScore(2));
*/      
   }
}