Array vs ArrayList vs Vector

April 11, 2006 at 9:10 pm · Filed under Software Engineer in me, Server Side, Java

I was just browsing through some of my old notes about the ‘research’ I did sometime back on various data structures available in java for handling dynamic data sets. Thought may be this could be helpful to somebody else as well. There are situations in code where you need to handle the data that grows during run time. Usually, as much as possible I prefer arrays to handle any homogeneous collection of elements, as they are fast to execute, have implicit type check and easy to handle. But they fail in situations where the size of data is unknown at compile time. The obvious choices available with java are ArrayLists or Vectors. Or I should say ArrayLists or Vectors?

Most of the time, people use both these data structures interchangeably. Even the documentation say that the ‘only’ difference between an ArrayList and a Vector is just that Vectors are synchronized, and there is no much difference. Here is what I found out

Similarities between ArrayLists and Vectors

• Both can grow up during run time.
• Both implement List interface.
• With both, it is easier to remove or add elements at the end or start, but if you try to add or remove elements somewhere at middle of collection, they suffer performance wise. (Use LinkedLists if your programme need to do that a lot, but LinkList requires more memory and computation)

Now the differences

• The major difference, as the documentation says, is just that vectors are synchronized. Now what does that mean, this means that if more than one thread in your code is to use that data, you are in trouble with ArrayList as the data is asynchronous. Though there are ways by which you can make your ArrayLists synchronous, but by default they are not. The obvious downside with vectors is the additional computation to handle threads.
• The other difference is that with vectors, you can specify the incremental value, which is the amount with which the data structure will grow during the runtime. But with ArrayLists you have no option but to accept default that is the list will grow up 50% of original size everytime it needs additional space. It is advisable in both the cases to choose the initial size carefully.

My recommendation will be to use Arrays as much as possible, as they are fast and simple; of course you can not do that in cases where data set is completely dynamic. In these cases, go for ArrayList if your code is ‘threadsafe’ else Vectors or synchronous ArrayLists are suitable.