Array or List in Java. Which is faster?

Question

I have to keep thousands of strings in memory to be accessed serially in Java. Should I store them in an array or should I use some kind of List ?

Since arrays keep

Answer 1

I wrote a little benchmark to compare ArrayLists with Arrays. On my old-ish laptop, the time to traverse through a 5000-element arraylist, 1000 times, was about 10 milliseconds slower than the equivalent array code.

So, if you're doing nothing but iterating the list, and you're doing it a lot, then maybe it's worth the optimisation. Otherwise I'd use the List, because it'll make it easier when you do need to optimise the code.

n.b. I did notice that using for String s: stringsList was about 50% slower than using an old-style for-loop to access the list. Go figure... Here's the two functions I timed; the array and list were filled with 5000 random (different) strings.

private static void readArray(String[] strings) {
    long totalchars = 0;
    for (int j = 0; j < ITERATIONS; j++) {
        totalchars = 0;
        for (int i = 0; i < strings.length; i++) {
            totalchars += strings[i].length();

        }
    }
}

private static void readArrayList(List stringsList) {
    long totalchars = 0;
    for (int j = 0; j < ITERATIONS; j++) {
        totalchars = 0;
        for (int i = 0; i < stringsList.size(); i++) {
            totalchars += stringsList.get(i).length();
        }
    }
}