Java class variable that tracks number of objects instantiated

Question

I have this class, Student, with the variable StudentID:

public class Student extends Person{
  int studentID = 0;
  int level;

  public Student(){

  }         


        

Answer 1

Make the studentID a static member

Static members are kept throughout each instance of the class no matter how many instances of the clas there are.

   public class Student extends Person{
      static int studentID = 0;
      int level;

      public Student(){

      }

      public Student(String fName, String lName, int gLevel){
        super(fName, lName);
        if(gLevel >= 0 && gLevel <= 12){
          level = gLevel;
        }
        studentID++;
      }
      public int getLevel(){
        return level;
      }
      public String toString(){
        String toReturn;
        toReturn = super.toString() + "\n   Grade Level: " + level + "\n   ID #: " + studentID;
        return toReturn;
      }
    }

Answer 2

Add a static counter and initialize studentID with it, incrementing it in the process :

public class Student extends Person{
  static counter = 1;
  int studentID = counter++;
  ...

Answer 3

You need a static variable to keep track of the number of students objects created.

public class Student extends Person{

    /* Number of students objects created */
    private static int studentCount = 0;   
    int studentID = 0;
    int level;

    public Student(String fName, String lName, int gLevel){
        super(fName, lName);
        if(gLevel >= 0 && gLevel <= 12){
            level = gLevel;
        }
        studentID = Student.getNextStudentId();
    }

    private static synchronized int getNextStudentId() {
        /* Increment the student count and return the value */
        return ++studentCount;
    }
}