Array vs ArrayList in performance [duplicate]

Answer 1

From here:

ArrayList is internally backed by Array in Java, any resize operation in ArrayList will slow down performance as it involves creating new Array and copying content from old array to new array.

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In terms of performance Array and ArrayList provides similar performance in terms of constant time for adding or getting element if you know index. Though automatic resize of ArrayList may slow down insertion a bit Both Array and ArrayList is core concept of Java and any serious Java programmer must be familiar with these differences between Array and ArrayList or in more general Array vs List.

Answer 2

I agree with somebody's recently deleted post that the differences in performance are so small that, with very very few exceptions, (he got dinged for saying never) you should not make your design decision based upon that.

In your example, where the elements are Objects, the performance difference should be minimal.

If you are dealing with a large number of primitives, an array will offer significantly better performance, both in memory and time.

Answer 3

It is pretty obvious that array[10] is faster than array.get(10), as the later internally does the same call, but adds the overhead for the function call plus additional checks.

Modern JITs however will optimize this to a degree, that you rarely have to worry about this, unless you have a very performance critical application and this has been measured to be your bottleneck.

Answer 4

When deciding to use Array or ArrayList, your first instinct really shouldn't be worrying about performance, though they do perform differently. You first concern should be whether or not you know the size of the Array before hand. If you don't, naturally you would go with an array list, just for functionality.

Answer 5

Arrays are better in performance. ArrayList provides additional functionality such as "remove" at the cost of performance.