Array vs ArrayList in performance [duplicate]

Question

Which one is better in performance between Array of type Object and ArrayList of type Object?

Assume we have a Array of Animal objects : Animal animal[] and a arraylist : ArrayList list<Animal>

Now I am doing animal[10] and list.get(10) which one should be faster and why?

Answer 1

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 2

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.