Vector vs ArrayList in Java

In Java, both Vector and ArrayList are dynamic arrays, with the main differences between them being the following points:

1. Thread safety: Vector is thread-safe, meaning it can be used in a multi-threaded environment, while ArrayList is not thread-safe. In a multi-threaded environment, if thread safety is needed, Vector should be used; if thread safety is not necessary, ArrayList will offer better performance.
2. Dynamic Growth: Both Vector and ArrayList have the ability to grow dynamically, but they do so in different ways. When needing to grow, Vector will double its capacity, while ArrayList will increase by 50%. This means that when the capacity is insufficient, Vector grows slower than ArrayList.
3. Initial Capacity: Vector has an initial capacity of 10, while ArrayList has an initial capacity of 0. This means that Vector will occupy a certain amount of memory space when created, while ArrayList will not occupy memory space when created.
4. Iterators: Both Vector and ArrayList have iterators to traverse the elements in the collection, but their iterator implementations differ. The iterator of Vector is safe, meaning you can modify the collection during iteration; while the iterator of ArrayList is fail-fast, meaning if you modify the collection during iteration, a ConcurrentModificationException will be thrown.

In general, Vector is suitable for scenarios in a multi-threaded environment that require thread safety, while ArrayList is suitable for scenarios in a single-threaded environment that require high performance.