Collection that loses oldest elements on add()

Question

I'm looking for a Java class that implements Collection and loses oldest elements when I add() a new one, if total number of elements is bigger than X. Does it exist or I have to implement it myself?

I need a thread-safe one.

Possible duplicate of [Java - Ring Buffer](http://stackoverflow.com/questions/7266042/java-ring-buffer) — DavidPostill, Jul 31 '14 at 13:09
possible duplicate of [Size-limited queue that holds last N elements in Java](http://stackoverflow.com/questions/5498865/size-limited-queue-that-holds-last-n-elements-in-java) — Andrew Stubbs, Jul 31 '14 at 13:10
Possible duplicate of [Thread-safe circular buffer in Java](http://stackoverflow.com/questions/11079210/thread-safe-circular-buffer-in-java) — DavidPostill, Jul 31 '14 at 13:13
[This](http://www.museful.net/2012/software-development/circulararraylist-for-java) might help — Mustafa sabir, Jul 31 '14 at 13:15

score 16 · Accepted Answer · edited Mar 01 '18 at 13:27

16

Apart from Linkedhasmap if you are looking for list type solution, Google guava has EvictingQueue. And for thread safety you must wrap it in a synchronized wrapper (Queues#synchronizedQueue).

EvictingQueue<String> q = EvictingQueue.create(3);
Queue<String> syncQ =  Queues.synchronizedQueue(q);
syncQ.add("one");
syncQ.add("two");
syncQ.add("three");
syncQ.add("four");
System.out.println(q); // Prints [two, three, four]

edited Mar 01 '18 at 13:27

tro

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answered Jul 31 '14 at 13:17

Syam S

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I think you could achieve that by `Queues.synchronizedQueue(q);` again from guava. – Syam S Jul 31 '14 at 13:23

score 3 · Answer 2 · edited Jul 31 '14 at 13:13

3

CircularFifoQueue is a first-in first-out queue with a fixed size that replaces its
oldest element if it is full.

edited Jul 31 '14 at 13:13

akash

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answered Jul 31 '14 at 13:11

David Pullar

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score 3 · Answer 3 · answered Jul 31 '14 at 13:15

You can use the LinkedHashMap to do precisely that, quoting the Javadoc:

// Sample use: this override will allow the map to grow up to 100 entries and then delete the 
// eldest entry each time a new entry is added, maintaining a steady state of 100 entries.

 private static final int MAX_ENTRIES = 100;

 protected boolean removeEldestEntry(Map.Entry eldest) {
    return size() > MAX_ENTRIES;
 }

for thread safe-ness you can wrap it using Collections.synchronizedmap().

dimitrisli · Answer 4 · 2019-06-01T19:06:06.827

0

I've used EvictingQueue added at v.15 of Google Guava to implement Moving Average functionality in the past.

It is not thread-safe though.

edited Jun 01 '19 at 19:06

answered Jul 31 '14 at 13:20

dimitrisli

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that's a 404 - where did it go? Did Google remove it ? – Someone Somewhere Jun 01 '19 at 15:19
@SomeoneSomewhere thanks - replaced it with the new location of the javadocs – dimitrisli Jun 01 '19 at 19:06

Collection that loses oldest elements on add()

4 Answers4