How to avoid duplicate values from ArrayList in Java?

This is one of the good interview question. I have faced many times this question in HCL & TCS interview. So frnds, let's see the following answer:

ArrayListDemo1.java

import java.util.*;
public class ArrayListDemo1 {

public static void main(String[] args)
{
ArrayList al = new ArrayList();

     al.add("Prajukta");
     al.add("Bishnupriya");
     al.add("Nitasha");
     al.add("Prajukta");
     al.add("Prajukta");      //Duplicate
     al.add("Prajukta");     //Duplicate

     ArrayList al2 = new ArrayList(new HashSet(al));

    Iterator it= al2.iterator();
    while(it.hasNext())
    {
    System.out.println(it.next());
    }

}
}

Output 
Prajukta
Bishnupriya
Nitasha