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Why is Java Vector considered a legacy class, obsolete or deprecated?
Isn't its use valid when working with concurrency?
And if I don't want to manually synchronize objects and just want to use a thread-safe collection without needing to make fresh copies of the underlying array (as CopyOnWriteArrayList does), then is it fine to use Vector?
What about Stack, which is a subclass of Vector, what should I use instead of it?
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This is because Vector synchronizes on each operation and does not synchronize the whole Vector instance itself. This is not desired in real-world applications, where the whole set of operations needs to be synchronized and not individual operations.
They are obsolete, but they are not deprecated.
Vector class is often considered as obsolete or “Due for Deprecation” by many experienced Java developers. They always recommend and advise not to use Vector class in your code. They prefer using ArrayList over Vector class.
Stack is a subclass of Vector that implements a standard last-in, first-out stack. Stack only defines the default constructor, which creates an empty stack. Stack includes all the methods defined by Vector, and adds several of its own.
Vector synchronizes on each individual operation. That's almost never what you want to do.
Generally you want to synchronize a whole sequence of operations. Synchronizing individual operations is both less safe (if you iterate over a Vector, for instance, you still need to take out a lock to avoid anyone else changing the collection at the same time, which would cause a ConcurrentModificationException in the iterating thread) but also slower (why take out a lock repeatedly when once will be enough)?
Of course, it also has the overhead of locking even when you don't need to.
Basically, it's a very flawed approach to synchronization in most situations. As Mr Brian Henk pointed out, you can decorate a collection using the calls such as Collections.synchronizedList - the fact that Vector combines both the "resized array" collection implementation with the "synchronize every operation" bit is another example of poor design; the decoration approach gives cleaner separation of concerns.
As for a Stack equivalent - I'd look at Deque/ArrayDeque to start with.
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Vector was part of 1.0 -- the original implementation had two drawbacks:
1. Naming: vectors are really just lists which can be accessed as arrays, so it should have been called ArrayList (which is the Java 1.2 Collections replacement for Vector).
2. Concurrency: All of the get(), set() methods are synchronized, so you can't have fine grained control over synchronization.
There is not much difference between ArrayList and Vector, but you should use ArrayList.
From the API doc.
As of the Java 2 platform v1.2, this class was retrofitted to implement the List interface, making it a member of the Java Collections Framework. Unlike the new collection implementations, Vector is synchronized.
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