Why Is Java Vector (And Stack) Class Considered Obsolete or Deprecated

Why is Java Vector (and Stack) class considered obsolete or deprecated?

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.

Why is java.util.Stack not marked as deprecated?

The Javadoc class documentation for java.util.Stack as per Java SE 14 does come with this guidance:

A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class. For example:

  Deque<Integer> stack = new ArrayDeque<Integer>();

Vector is an obsolete Collection

First of all, although Vector is mostly obsoleted by ArrayList, it is still perfectly legal to use, and your project should run just fine.

As noted, however, it is not recommended to use. The main reason for this is that all of its methods are synchronized, which is usually useless and could considerably slow down your application. Any local variable that's not shared outside the scope of the method can safely be replaced with an ArrayList. Method arguments, return values and data members should be inspected closely before being replaced with ArrayList, lest you unwittingly change the synchronization semantics and introduce a hard-to-discover bug.

Java 6 SE are vectors obsolete?

Use of Vectors have been discouraged for some time now. They are replaced by ArrayList, which has more or less the same functionality (but isn't synchronised).

Why to use a Deque instead of inbuilt Stack?

Java generics were added after initial implementations of collections; Stack is from Java 1.0 - and rather then break existing code when they added generics, it was decided to add classes that duplicate functionality (but provide a consistent API). That is why you should prefer a Deque - it provides an API consistent with all of the other Java Collections.

Should Vector be deprecated?

While it is rarely a good idea to use Vector in new code, there is no pressing need to deprecate. While the new collections classes are superior, using the Vector class doesn't actually break anything.

Furthermore, there are a number of other standard Java APIs that depend on the Vector API, and there are doubtless hundreds of thousands of customer and third party applications that use it as well.

Basically, deprecating Vector would be unnecessarily disruptive. There is no need to push people into changing code that works reliably, if marginally slower.

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It has been suggested / implied that they could deprecate Vector without (ever) actually removing it. But the problem is that deprecation warnings create real work for real people. If this is done unnecessarily, busy people will start suppressing the warnings by default. (Recall the story of the boy who cried wolf .... )

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