Get last X items of a list in java

Question

I can only seem to find answers about last/first element in a list or that you can get a specific item etc.

Lets say I have a list of 100 elements, and I want to return the last 40 elements. How do I do that? I tried doing this but it gave me one element..

Post last40posts = posts.get(posts.size() -40);

Refer to http://stackoverflow.com/questions/2895342/java-how-can-i-split-an-arraylist-in-multiple-small-arraylists. You can use `subList` from `size() - 40` to `size()` to get the last 40 elements. Also http://stackoverflow.com/questions/1279476/truncating-a-list-to-a-given-number-of-elements-in-java (or http://stackoverflow.com/questions/12099721/how-to-use-sublist) — Tunaki, May 13 '16 at 21:16
Possible duplicate of [Java: how can I split an ArrayList in multiple small ArrayLists?](https://stackoverflow.com/questions/2895342/java-how-can-i-split-an-arraylist-in-multiple-small-arraylists) — A Jar of Clay, May 15 '19 at 14:52

ΦXocę 웃 Пepeúpa ツ · Accepted Answer · 2017-09-26T13:45:11.403

8

Do use the method sub list

List<Post> myLastPosts = posts.subList(posts.size()-40, posts.size());

edited Sep 26 '17 at 13:45

answered May 13 '16 at 21:21

ΦXocę 웃 Пepeúpa ツ

47,427
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4

Strictly, this gets the last 39 elements of the list, as the second argument of `subList` is exclusive. – Andy Turner May 13 '16 at 21:35
1

what happens if the list is of smaller length than the size we want, ie. the list contains only 5 elements. – Bruno Finger Dec 16 '19 at 15:01
@BrunoFinger if that happens, you will get and IndexOutOfBoundsException. But i would like to know how to fix it. – Agustin Rodriguez Nov 16 '22 at 14:22
Why did you spam the tag arraylist if this is for simpe lists only and not ArrayList bro? – Raul Chiarella Apr 18 '23 at 02:17

score 6 · Answer 2 · answered Feb 28 '19 at 15:26

(To complete Ankit Malpani answer) If 40 is provided by our lovely users, then you will have to restrict it to the list size:

posts.subList(posts.size()-Math.min(posts.size(),40), posts.size())

Another way to show it:

@Test
public void should_extract_last_n_entries() {
    List<String> myList = Arrays.asList("0","1","2","3","4");
    int myListSize = myList.size();
    log.info(myList.subList(myListSize,myListSize).toString());   // output : []
    log.info(myList.subList(myListSize-2,myListSize).toString()); // output : [3, 4]
    log.info(myList.subList(myListSize-5,myListSize).toString()); // output : [0, 1, 2, 3, 4]
    int lastNEntries = 50; // now use user provided int
    log.info(myList.subList(myListSize-Math.min(myListSize,lastNEntries),myListSize).toString());
                          // output : [0, 1, 2, 3, 4]
    // log.info(myList.subList(myListSize-lastNEntries,myListSize).toString());
                          // ouch IndexOutOfBoundsException: fromIndex = -45
}

Ankit Malpani · Answer 3 · 2016-05-13T21:43:53.203

1

Your code will give you only a single element. You need to use subList method like:

posts.subList(posts.size()-40, posts.size())

edited May 13 '16 at 21:43

answered May 13 '16 at 21:34

Ankit Malpani

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Get last X items of a list in java

3 Answers3