How to avoid duplicates from List / ArrayList

Hii frnds…this is the question that I have faced many times in interview, very popular frequently asked question. Let’s see in detail.

ArrayListExample.java

package java8s;

import java.util.*;

public class ArrayListExample {

          public static void main(String[] args) {

                  

                  

                                      ArrayList al = new ArrayList();

                    

                                            al.add("First");

                                            al.add("Second");

                                            al.add("Third");

                                            al.add("First");     //Duplicate

                                            al.add("First");     //Duplicate

                    

                                          

                                              ArrayList al1 = new ArrayList(new HashSet(al));     

                    

                                           // ArrayList al2 = new ArrayList(new LinkedHashSet(al));     

                    

                                           Iterator it= al1.iterator();

                                           while(it.hasNext())

                                           {

                                                 System.out.println(it.next());

                                           }

                    

                             }

                  

          }

Output:

Second

Third

First