What is the use of Vector where as Arraylist can be Synchronized?

[Subhash Pavuskar]

Hi All,
It may silly question but any how need to know more details.

The difference between Vector and ArrayList is thread safe whereas Arraylist is not. but as the arraylist can be make synchronized what is the necessity of Vector?

also Enumeration and Iterator?

thanks in advance.

[Campbell Ritchie]

Exactly. Don’t use Vector, Enumeration, Stack or Hashtable.

[Randall Twede]

Vector existed before there was any such thing as ArrayList. in the beginning it was either Vector or Array, that was it!
as for iterators, i never liked them anyway. i am so glad we now have "for each" so we no longer need them

[Campbell Ritchie]

Randall Twede wrote: . . . i am so glad we now have "for each" so we no longer need them [Iterators]

But the for‑each loop always uses an Iterator. It is simply at one remove where you don’t notice it.

[Rishi Shah]

No, ArrayList cannot truly be synchronized without more effort than simply using a Vector.

[Martin Vashko]

I still strongly prefer ArrayList over Vector.

Firstly, Collections.synchronizedList(new ArrayList()); does not look like an unreasonable amount of effort to me.

Secondly, when someone spots this construction, it is immediately clear the ArrayList is intentionally synchronized and is therefore going to be used by multiple threads. If I used a Vector instead, the developer to come after me might not know for sure whether I had a bout of nostalgia, or I really use Vector just to get synchronized access.

For me, Vector equals legacy code.

[Randall Twede]

nah! you are kidding me. how can such a succinct, non-verbose, language like Java have legacy code?

[Campbell Ritchie]

It was written as legacy code when it was new

[Rishi Shah]

Martin Vajsar wrote:I still strongly prefer ArrayList over Vector.

Firstly, Collections.synchronizedList(new ArrayList()); does not look like an unreasonable amount of effort to me.

Secondly, when someone spots this construction, it is immediately clear the ArrayList is intentionally synchronized and is therefore going to be used by multiple threads. If I used a Vector instead, the developer to come after me might not know for sure whether I had a bout of nostalgia, or I really use Vector just to get synchronized access.

For me, Vector equals legacy code.

Yeah, I stand corrected. Vectors are pre 1.2 and shouldn't really be used with the newer collections in the Java API.

I wonder why it's not deprecated?

Here is a quote from Jon Skeet explaining (http://stackoverflow.com/a/1386288/603732):

Jon Skeet wrote:
Vector synchronizes on each individual operation. That's almost never what you want to do.

Generally you want to synchronize a whole sequence of operations. Synchronizing individual operations is both less safe (if you iterate over a Vector, for instance, you still need to take out a lock to avoid anyone else changing the collection at the same time) but also slower (why take out a lock repeatedly when once will be enough)?

Of course, it also has the overhead of locking even when you don't need to.

Basically, it's a very flawed approach to synchronization in most situations. As MrSpandex pointed out, you can decorate a collection using the calls such as Collections.synchronizedList - the fact that Vector combines both the "resized array" collection implementation with the "synchronize every operation" bit is another example of poor design; the decoration approach gives cleaner separation of concerns.

As for a Stack equivalent - I'd look at Deque/ArrayDeque to start with.

[Paul Clapham]

Rishi Shah wrote:I wonder why it's not deprecated?

It isn't deprecated because there's an awful lot of existing code in the standard API which uses it. See DefaultTableModel for an example. Since the published API of that class involves Vector parameters, it can't ever be changed. Of course, DefaultTableModel itself could be deprecated in favour of a new design which used List instead of Vector, but that would be a lot of work for really not much value.

[Campbell Ritchie]

Can’t they overload the method to take a List parameter.