Why is Java Vector and Stack class considered obsolete or deprecated

Question

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

User · Answer

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

User · Answer

You can use the synchronizedCollection List method in java util Collection to get a thread-safe collection from a non-thread-safe one

User · Answer

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

User · Answer

java util Stack inherits the synchronization overhead of java util Vector  which is usually not justified   It inherits a lot more than that  though   The fact that java util Stack extends java util Vector is a mistake in object-oriented design   Purists will note that it also offers a lot of methods beyond the operations traditionally associated with a stack  namely  push  pop  peek  size    It s also possible to do search  elementAt  setElementAt  remove  and many other random-access operations   It s basically up to the user to refrain from using the non-stack operations of Stack   For these performance and OOP design reasons  the JavaDoc for java util Stack recommends ArrayDeque as the natural replacement    A deque is more than a stack  but at least it s restricted to manipulating the two ends  rather than offering random access to everything

User · Answer

Besides the already stated answers about using Vector  Vector also has a bunch of methods around enumeration and element retrieval which are different than the List interface  and developers  especially those who learned Java before 1 2  can tend to use them if they are in the code  Although Enumerations are faster  they don t check if the collection was modified during iteration  which can cause issues  and given that Vector might be chosen for its syncronization - with the attendant access from multiple threads  this makes it a particularly pernicious problem  Usage of these methods also couples a lot of code to Vector  such that it won t be easy to replace it with a different List implementation

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

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