Arraylist vs Vector

[nitinram agarwal]

Hi,
need to have some kind of clear understanding regarding the synchronized behavior of arraylist and vector. when we say that Vector is synchronized and arraylist is not, does it mean that
1. when multiple threads access vector and modify its contents, one thread will see updated copy of the vector before modification
2. when multiple threads access arraylist and modify its contents, one thread will see updated copy of the arraylist before modification only if the arraylist is properly synchronized.

is there anything more than what I said?

Regards,

[Mohamed Sanaulla]

nitinram agarwal wrote:Hi,
need to have some kind of clear understanding regarding the synchronized behavior of arraylist and vector. when we say that Vector is synchronized and arraylist is not, does it mean that
1. when multiple threads access vector and modify its contents, one thread will see updated copy of the vector before modification
2. when multiple threads access arraylist and modify its contents, one thread will see updated copy of the arraylist before modification only if the arraylist is properly synchronized.

is there anything more than what I said?

Regards,

I found a related article. Might be explaining more than just Synchronization issue. If you have access to the source code for Vector and ArryaList implementation it will be lot helpful to see how the methods- which modify the list contents are implemented.

[Wouter Oet]

The methods on the Vector are synchronized meaning that only 1 thread can access it at a time. But a couple of successive method calls need external synchronization (e.g. checking if an element exists and if not inserting it).

So it's not who sees what but who can access the object.

[nitinram agarwal]

so you mean even multiple threads cannot read the vector simultaneously. I was under the impression that its exlusive modification on the vector.

[Wouter Oet]

But it's also an exclusive read. Otherwise it's not properly synchronized.