Change from ArrayList to Vector

Question

I'm working on an android game and I just noticed that since onTouchEvent runs on the UI thread, and the update/render methods are ran from a separate threads, both of them update an ArrayList which contains the entities. So obviously they conflict if they happen to modify the list at the same time.

I read that Vector class is used exactly the same as ArrayList with the only difference that Vector is synchronized, ergo they wont conflict. Is that true? if so, does it have any performance issue or something that I should be concerned about? I have never used Vector class before.

EDIT: what I actually meant was change from

ArrayList<Obj> list = new ArrayList<Obj>();

to

Vector<Obj> list = new Vector<Obj>()

But as the answers say, Vector is not recommended to use. The selected answer solved my issue.

Technically it's not, but really it's an ancient and depending on the use case a `List` from the `Concurrent` package is probably going to be better. — Brian Roach, Jul 04 '13 at 21:54
Jon Skeet explains why not to use Vector here: http://stackoverflow.com/q/1386275/1065197 — Luiggi Mendoza, Jul 04 '13 at 21:55

score 39 · Answer 1 · answered Apr 04 '14 at 09:43

39

For those who have to fight with legacy code do just the following:

new Vector<Obj>(anyThingWhichImplemntsCollection);

answered Apr 04 '14 at 09:43

Sergio Gabari

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score 9 · Accepted Answer · edited May 23 '17 at 12:02

9

It's oldie Vector try to not use Vector instead use

synchronizedList

Example :

list = Collections.synchronizedList(list);

Vector is considered obsolete and deprecated read Why vector is considerer obsolete?

edited May 23 '17 at 12:02

Community

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answered Jul 04 '13 at 21:53

nachokk

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This solves it: `List list = Collections.synchronizedList(new ArrayList());` – Christopher Francisco Jul 04 '13 at 22:16
yep , you got it ;) read Jon Skeet answer in the link i post, is interesting :) – nachokk Jul 04 '13 at 22:18
Yep, it's pretty interesting. It actually helped me a little to understand about the `synchronized` block. I'm kinda new to it (: – Christopher Francisco Jul 04 '13 at 22:20
@ChristopherFrancisco in the other link synchronizedList if you read says that if you want to iterate the collection you should put synchronized the block – nachokk Jul 04 '13 at 22:23
exactly, basically to iterate the list I put everything into `synchronized(list) { //code }`. By the way, can I iterate the list using a `for()` loop? or do I HAVE to use the iterator class ? – Christopher Francisco Jul 04 '13 at 22:26
i think is the same is just the syntaxis, semantics is the same, behind has an iterator the `for()`, try and error :D – nachokk Jul 04 '13 at 22:30
I'll go with the `for()` :D – Christopher Francisco Jul 04 '13 at 22:41

score 2 · Answer 3 · answered Jul 04 '13 at 21:53

2

List<Foo> list = new Vector<Foo>(new ArrayList<Foo>());

should work. Both of those structures implements List interface.

But like other people suggested, this is not recomended.

answered Jul 04 '13 at 21:53

ArturSkowronski

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That code snippet doesn't make much sense. It would add the elements from an empty `ArrayList` to the created `Vector` instance. – nif Jul 04 '13 at 21:56
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As much as I understood this was what Christopher Francisco asked for. Vector with data from ArrayList. New Array List is there only a kind of mock. – ArturSkowronski Jul 04 '13 at 21:59
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When using a legacy library which accepts Vector one have to convert List to Vector and this answer helps. – kiri Apr 16 '14 at 01:42

score 0 · Answer 4 · answered Jul 05 '13 at 09:11

As already mentioned by nachokk, synchonizedList will do the trick. synchronizedList will return a wrapper around your list, so no copying is done.
The downside is that only one call to the list can be done at a time. Two reads at the list will be sequential even if they could be done in parallel. Synchronized blocks always means a little overhead and decreaces performance if called often.

Another option would be to use a concurrent list. This means a copy in the first place, but access performance could be dramatically improved. If you have many read requests (e.g. for paintings), a CopyOnWriteArrayList will be a good choice. Reads are nearly as fast as a normal ArrayList and won't be blocked. Writes to the list will be sequential and expensive, since they have to copy the whole array.
Another good point for the CoWArrayList is that you can iterate without catching a ConcurrentModificationException. The Iterator returned by iterator() will always use the same backing array, even if the list has changed.

Change from ArrayList to Vector

4 Answers4