Understanding TreeSet when compareto returns 0

Question

I have created a Student class like this:

public class Student implements Comparable {

    private String firstName;
    private String lastN         


        

Answer 1

Since you have compared only first name in compareTo method, you need

 @Override
public int compareTo(Student student) {
    int comp = this.firstName.compareTo(student.firstName);
    if(comp==0) return this.lastName.compareTo(student.lastName);
    return comp;
}

when compareTo returns 0, treeSet assumes that its duplicate.