Why does TreeSet throw a ClassCastException?

Question

I am trying to add two \'Employee\' objects to a TreeSet:

Set s = new TreeSet();
s.add(new Employee(1001));
s.add(new Employe         


        

Answer 1

//class Employee
    public class Employee implements Comparable{
    int id;

    Employee(int id){
    this.id=id;
    }

    public int compareTo(Employee e){ //implementing abstract method.
    if(id>e.id){
    return 1;
    }
    return 0;
    }


//class TreeSet

    Set emp =new TreeSet();

    Employee eobj1 = new Employee(2);
    Employee eobj2 = new Employee(3);
    emp.add(eobj1);
    emp.add(eobj2);

    for (Student ss:emp) {
    System.out.println(ss.rollno);
    }
}
//output: 2
//        3