Collection that will maintain insertion order and no duplicates

Question

In Java collection which collection will doesn't allow duplicates and which also preserve insertion order of data?

Does this help? http://stackoverflow.com/questions/8712469/any-implementation-of-ordered-set-in-java — vikingsteve, May 10 '13 at 10:45
Why is this marked as a duplicate of 'Is there an insertion order preserving set in Java?' This is not a duplicate of that, that question asks about Sets and Lists; this question is about all collections. — searchengine27, Apr 10 '15 at 17:21

score 31 · Accepted Answer · answered May 10 '13 at 10:47

LinkedHashSet

As per the documentation

This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order)

score 22 · Answer 2 · answered May 10 '13 at 10:45

22

LinkedHashSet does both of them

Set set = new LinkedHashSet();

answered May 10 '13 at 10:45

hamid

2,033
4
22
42

4

A `HashSet` won't preserve the order of insertion. – Jeff Foster May 10 '13 at 10:46
[`HashSet`](http://docs.oracle.com/javase/7/docs/api/java/util/HashSet.html) doesn't preserve insertion order. – Mark Rotteveel May 10 '13 at 10:46
Yes, sorry got too excited :) – hamid May 10 '13 at 10:48
Unfortunately your edit did not register as an edit so I cannot retract my downvote. You might want to consider a more substantial edit of your answer. – Mark Rotteveel May 11 '13 at 07:29

score 10 · Answer 3 · answered May 10 '13 at 10:45

A LinkedHashSet should fit the bill.

Hash table and linked list implementation of the Set interface, with predictable iteration order. This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order).

score 6 · Answer 4 · edited Nov 04 '17 at 08:53

You can check LinkedHashSet for this purpose.

A Set will not allow duplicate values. And LinkedHashSet will preserve insertion order.

Hash table and linked list implementation of the Set interface, with predictable iteration order. This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order). Note that insertion order is not affected if an element is re-inserted into the set. (An element e is reinserted into a set s if s.add(e) is invoked when s.contains(e) would return true immediately prior to the invocation.)

score 2 · Answer 5 · answered May 10 '13 at 10:47

Use

public class LinkedHashSet<E> extends HashSet<E>

Basically Set won't allow duplicates and

This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order)

http://docs.oracle.com/javase/6/docs/api/java/util/LinkedHashSet.html

score 2 · Answer 6 · answered May 10 '13 at 10:47

2

You want an ordered set, which is implemented by LinkedHashSet.

answered May 10 '13 at 10:47

Stefano Sanfilippo

32,265
7
79
80

Collection that will maintain insertion order and no duplicates

6 Answers6

Linked