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Below is my Student class class Student implements Comparable { String name; int rollNo; @Override public int compareTo(Object obj) { return ((Student)obj).name.compareTo(this.name); } } latest modification: but still no getting the right result @Override public int compareTo(Object obj) { Student s = (Student) obj; if (name.equals(s.name)) { // achieving uniqueness return 0; } else { if (rollNo < s.rollNo) { return -1; } else if (rollNo > s.rollNo) { return 1; } else { // this makes `name` the second ordering option. // names don't equal here return name.compareTo(s.name); } } } If I create object of TreeSet<Student>, I am getting sorted list of Student objects based on unique name & ordered by name also. But I need unique student-name in my TreeSet<Student> with order by student-rollNo. Is it possible with Comparator? Can anybody help me, Every suggestion is appreciated. Thanks. UPDATE: here is the complete program: public class Student implements Comparable { int rollNo; String name; Student(String n,int rno) { rollNo=rno; name=n; } /** * @param args */ public static void main(String[] args) { TreeSet<Student> ts = new TreeSet<Student>(); ts.add(new Student("bbb",2)); ts.add(new Student("aaa",4)); ts.add(new Student("bbb",2)); ts.add(new Student("ccc",3)); ts.add(new Student("aaa",1)); ts.add(new Student("bbb",2)); ts.add(new Student("bbb",5)); System.out.println(ts); } @Override public int compareTo(Object obj) { Student s = (Student) obj; if (name.equals(s.name)) { // achieving uniqueness return 0; }

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