CODEWITHSUNDEEP
javavectorarraylist
SomeDude
SomeDude

Reputation: 14238

Java synchronized ( ArrayList ) or Vector?

I know that ArrayList is not synchronized, but I can access it in a synchronized way as :

synchronized( arraylist )
{
   arraylist.add( "new item" );
}

or I can use a vector instead - which I see from every blog that it should be avoided.

Please let me know your thoughts

Upvotes: 1

Views: 1669

Answers (2)

wassgren
wassgren

Reputation: 19221

Yes, you can access a List and make it synchronized by using blocks as you have described. Note that you must also synchronize when reading from the list in order to be totally safe.

An alternative (and IMO better) approach is to use one of the following:

Alternative 1: Collections.synchronizedList:

List<SomeType> sList = Collections.synchronizedList(arrayList);
sList.add(...); // synchronized, no synchronized-block needed

The returned list will be synchronized for updates but iterations must still be in a synchronized block:

// Iterating...
synchronized (sList) {
    for (SomeType s : sList) {
        // do stuff
    }
}

You can find the JavaDocs here

Alternative 2: CopyOnWriteArrayList:

You can find the JavaDocs here

A thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array.

The second alternative is obviously more memory-consuming if you perform a lot of writes.

Upvotes: 1

Luiggi Mendoza
Luiggi Mendoza

Reputation: 85779

There is a concurrent List implementation: CopyOnWriteArrayList that supports concurrency and is better than the options described above.

Still, I would recommend using another collection like a concurrent Queue through BlockingQueue and implemented by LinkedBlockingQueue. I would ask you to provide more info on your problem to get more accurate help.

Upvotes: 2

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