How to execute binary search on a vector ?

JAVA Program

import java.util.Collections;
import java.util.Vector;
public class Main {
	public static void main(String[] args) {
		Vector v = new Vector();
		v.add("X");
		v.add("M");
		v.add("D");
		v.add("A");
		v.add("O");
		Collections.sort(v);
		System.out.println(v);
		int index = Collections.binarySearch(v, "D");
		System.out.println("Element found at : " + index);
	}
}

Output

[A, D, M, O, X]
Element found at : 1