Is there a Java collection whose objects are unique (as in a set) but has the ability to get the index/position of a certain object(as in a list)?

Question

I have an ordered, unique, set of objects. I am currently using a TreeSet in order to get the ordering correct. However, sets do not have the ability to get index.

My current implementation is fine, but not necessarily intuitive.

TreeSet<T> treeSet = new TreeSet<T>(Comparable c);
// Omitted: Add items to treeSet //
int index = new ArrayList<T>(treeSet)().indexOf(object);

Is there an easier way to do this?

Answer 1

treeSet.headSet(object).size() should do the trick:

import java.util.SortedSet;
import java.util.TreeSet;

class Test {

  public static void main(String[] args) {

    SortedSet<String> treeSet = new TreeSet<String>();
    String first = "index 0";
    String second = "index 1";
    treeSet.add(first);
    treeSet.add(second);

    int one = treeSet.headSet(second).size();

    System.out.println(one);
    // 1
  }
}