import java.util.*; 

class Student implements Comparable<Student> {
  Student (double gpa) { 
    this.gpa = gpa; 
  }
  double gpa; 
  public String toString() {
    return "S(" + this.gpa + ")"; 
  } 
  public int compareTo(Student other) {
    return (int) (this.gpa - other.gpa); // wrong when the difference is less than 1
    // we just want to return 1, 0 or -1 depending on whether the difference is > 0, < 0 or == 0
    // so we could do this instead: double diff = this.gpa - other.gpa; and then 
    // return diff == 0.0 ? 0 : (int) Math.round(diff / Math.abs(diff)); // correct but convoluted
    // even better: if (diff > 0) return 1; else if (diff < 0) return -1; else return 0; 
  }
}

class One {
  public static void main(String[] args) {
    ArrayList<Student> a = new ArrayList<Student>(); 
    a.add(new Student(2.3)); 
    a.add(new Student(1.3)); 
    a.add(new Student(3.9)); 
    a.add(new Student(3.3)); 
    a.add(new Student(2.6)); 
    a.add(new Student(2.1)); 
    System.out.println( a ); 
    Collections.sort( a ); 
    System.out.println( a ); 

  } 
}