The methods of Vector are synchronized, the methods of ArrayList are not.

Bye
Michael

For a detailed discussion of Vector/ArrayList and
LinkedList, see this recent thread..
<http://www.javakb.com/Uwe/Forum.aspx/java-programmer/33059/Vector-vs-LinkedList

HTH

The java.util collections were redesigned for release 1.2, with a
consistent system of interfaces, Iterator instead of Enumeration, and no
synchronization unless you ask for it through
Collections.synchronizedList etc.

ArrayList is part of the newer design, and has no left overs from
earlier versions.

Vector is older. It was modified to fit into the new design as well as
possible, but had to maintain backwards compatibility. That includes
synchronization, as well as methods that duplicate functionality in
slightly different ways.

If you have a choice, use ArrayList. You need to be aware of Vector in
case you come across it in older code.

Patricia

The reason that ArrayList is a different class from Vector is that
Vector is older.  In the 1.2 release cycle, Java added the Collections
API; a set of various container implementations that follow a similar
organization.  The older Vector class violated several of the principles
of the new Collections API, and couldn't be fixed to follow them without
breaking compatibility with existing code.  Instead, a new class was
introduced.

The biggest difference is that Vector is synchronized automatically, so
that certain trivially simple multithreaded uses can be safely done (but
watch out! Most non-trivial things still require some more coordination
on your part.)  An ArrayList, by contrast, would need to be wrapped with
Collections.synchronizedList if you want its methods to be synchronized.  
IIRC, a second difference has to do with growth policy, and can affect
the performance of the implementation.