An ArrayList is a newer class than a Vector. A Vector is considered a legacy class in Java. The differences are...

Synchronization : Vector is synchronized, but the ArrayList is not synchronized. So an ArrayList has faster operations than a Vector.

Data Growth : Internally both an ArrayList and Vector use an array to store data. When an ArrayList is almost full it increases its size by 50% of the array size. Whereas a Vector increases it by doubling the underlying array size.