What is the difference between Vector and List in Java?

In Java, Vector and List are two separate interfaces, with the main difference between them being as follows:

1. Thread safety: Vector is thread-safe, meaning that multiple threads can access a Vector object simultaneously without causing inconsistencies in the data. In contrast, implementations of the List interface such as ArrayList and LinkedList are not thread-safe.
2. Expansion mechanism: When it needs to expand, Vector automatically increases its capacity to accommodate new elements. During expansion, Vector creates a new array and copies the elements from the old array to the new one. Similarly, ArrayList also automatically increases capacity during expansion, but it only increases by half of the current capacity. Unlike Vector and ArrayList, LinkedList does not have a fixed capacity and creates a new node each time an element is added.
3. Iterators: The iterators of Vector are synchronized, meaning that when using an iterator to traverse Vector, other threads cannot modify the contents of Vector. On the other hand, the iterators of ArrayList and LinkedList are not synchronized, allowing for the modification of the List’s contents while traversing it.
4. Performance: Because Vector is thread-safe, it requires synchronization during operations, leading to additional performance overhead. In single-threaded environments, ArrayList typically performs better than Vector because it does not require synchronization. LinkedList, on the other hand, may be more efficient than ArrayList in certain operations due to its use of a linked list implementation.

In general, if you need to share a List object among multiple threads and ensure thread safety, you can use Vector. If thread safety is not needed, you can use ArrayList or LinkedList, depending on the specific usage scenario and performance requirements.