Set

1. HashSet doesn’t maintain any kind of order of its elements.
2. TreeSet sorts the elements in ascending order.
3. LinkedHashSet maintains the insertion order. Elements gets sorted in the same sequence in which they have been added to the Set.

import java.util.LinkedHashSet;
public class LinkedHashSetExample {
     public static void main(String args[]) {
         // LinkedHashSet of String Type
         LinkedHashSet<String> lhset = new LinkedHashSet<String>();

         // Adding elements to the LinkedHashSet
         lhset.add("Z");
         lhset.add("PQ");
         lhset.add("N");
         lhset.add("O");
         lhset.add("KK");
         lhset.add("FGH");
         System.out.println(lhset);

         // LinkedHashSet of Integer Type
         LinkedHashSet<Integer> lhset2 = new LinkedHashSet<Integer>();

         // Adding elements
         lhset2.add(99);
         lhset2.add(7);
         lhset2.add(0);
         lhset2.add(67);
         lhset2.add(89);
         lhset2.add(66);
         System.out.println(lhset2);
    }
}

　　

[Z, PQ, N, O, KK, FGH]
[99, 7, 0, 67, 89, 66]

 http://beginnersbook.com/2013/12/linkedhashset-class-in-java-with-example/