ArrayList vs Vector : Which one to use?

Question

At the very beginning, I'll admit it that I'm an idiot; but there's one thing that I just can't seem to understand. I can't seem to find much difference between ArrayList and Vector other than this:

"...(This class is roughly equivalent to Vector, except that it is unsynchronized.)... "

in the javaDocs of ArrayList.

So, is this difference really an important factor in the way we apply these two similar classes when we consider the general scenario (i.e. ruling out the application in Thread-based programming)? Are there any other marked differences? If so, please tell me. If not, then which one is the most preferred or generally accepted approach?

Answer 1

Other than differences with synchronization, there is also a difference internally when you insert new elements. For both classes, the array within must be increased in size to prevent it from running out of room. Vectors double their size by default. ArrayLists increase their size by half their present size.

Edit:

Also, a couple answers mentioned that Vectors are thread safe. That's true to some extent, but the whole reason they're sort-of-deprecated (I think) is because they're not very useful for most synchronization needs, which is because it synchronizes on every operation (not safe). What you want to do usually is synchronize on a sequence of operations. Vectors don't do that (neither do ArrayLists though) so it's not really the way to go even in situations that require synchronization (basically it's out of your control).

Answer 2

According to Java API:

"it is recommended to use ArrayList in place of Vector"

Still you can get a synchronized version of a List with Collections:

Collections.synchronizedList(List<T> list)

for example

List list = Collections.synchronizedList(new ArrayList());

This returns a synchronized (thread-safe) list backed by the specified list.

Answer 3

The major difference between the two is that the vectors are synchronized, so they are thread-safe, and the ArrayLists are not. Both of them uses an array to store the data they contain, and so whenever you add something to it's content they will need to resize themselve, although they do that pretty efficiently, it is to be considered.

ArrayLists also have the advantage to be part of the Collection framework so you can use the Collection methods with it to sort, search, etc.

Hope this helps!

Answer 4

The only difference is the synchronization, if you are using the List in a threaded program you should use vector, but if not, ArrayList (or other not synchronized implementation of List).

The theoretical reason is that synchronization causes a worse performance of Vector than ArrayList.

Answer 5

Vector has been around since java 1.0

ArrayList was released with java 1.2

The preferred way is to use ArrayList.

If you are concerned about thread safe, you can synchronize it like this:

List list = Collections.synchronizedList(new ArrayList(...));