Difference between Vector and ArrayList in Java

Arraylist and Vector are two of most used class on java collection package and difference between Vector and ArrayList is one of the most frequently asked interview question on first round or phone interview. Though it’s quite a simple question in my opinion but knowledge of when to use Vector over ArrayList or ArrayList over Vector does matter if you are working on a project. In this article we will some point based differences between Vector and ArrayList and trying to understand the concept behind those differences. Ultimate goal is to familiarize yourself with distinguish property of ArrayList and Vector.

Before seeing differences between Vector and ArrayList, let's see some similarities between these two and why we can use ArrayList in place of Vector on certain scenario.

1) Vector and ArrayList are index based and backed up by an array internally.
2) Both ArrayList and Vector maintains the insertion order of element. Means you can assume that you will get the object in the order you have inserted if you iterate over ArrayList or Vector.
3) Both iterator and ListIterator returned by ArrayList and Vector are fail-fast.

Now let's see some key differences between Vector and ArrayList in Java

Key Differences between Vector and ArrayList in Java

1) First and foremost difference is Vector is synchronized and ArrayList is not, what it means is that all the method which structurally modifies Vector e.g. add () or remove () are synchronized which makes it thread-safe and allows it to be used safely in a multi-threaded environment. On the other hand ArrayList methods are not synchronized thus not suitable for use in multi-threaded environment.

2) ArrayList is faster than Vector. Since Vector is synchronized it pays price of synchronization which makes it little slow. On the other hand ArrayList is not synchronized and fast which makes it obvious choice in a single-threaded access environment. You can also use ArrayList in a multi-threaded environment if multiple threads are only reading values from ArrayList.

3) Whenever Vector crossed the threshold specified it increases itself by value specified in capacityIncrement field while you can increase size of arrayList by calling ensureCapacity () method.

4) Vector can return enumeration of items it hold by calling elements () method which is not fail-fast as opposed to iterator and ListIterator returned by ArrayList.

5) Another point worth to remember is Vector is one of those classes which comes with JDK 1.0 and initially not part of Collection framework but in later version it's been re-factored to  implement List interface so that it could become part of collection framework



Conclusion is use ArrayList wherever possible and avoids use of Vector until you have no choice.

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