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 came here to get a better feeling for the performance impact of using lists over arrays. I had to adapt code here for my scenario: array/list of ~1000 ints using mostly getters, meaning array[j] vs. list.get(j)

Taking the best of 7 to be unscientific about it (first few with list where 2.5x slower) I get this:

array Integer[] best 643ms iterator
ArrayList best 1014ms iterator

array Integer[] best 635ms getter
ArrayList best 891ms getter (strange though)

- so, very roughly 30% faster with array

The second reason for posting now is that no-one mentions the impact if you do math/matrix/simulation/optimization code with nested loops.

Say you have three nested levels and the inner loop is twice as slow you are looking at 8 times performance hit. Something that would run in a day now takes a week.

*EDIT Quite shocked here, for kicks I tried declaring int[1000] rather than Integer[1000]

array int[] best 299ms iterator
array int[] best 296ms getter

Using Integer[] vs. int[] represents a double performance hit, ListArray with iterator is 3x slower than int[]. Really thought Java's list implementations were similar to native arrays...

Code for reference (call multiple times):

    public static void testArray()
    {
        final long MAX_ITERATIONS = 1000000;
        final int MAX_LENGTH = 1000;

        Random r = new Random();

        //Integer[] array = new Integer[MAX_LENGTH];
        int[] array = new int[MAX_LENGTH];

        List list = new ArrayList()
        {{
            for (int i = 0; i < MAX_LENGTH; ++i)
            {
                int val = r.nextInt();
                add(val);
                array[i] = val;
            }
        }};

        long start = System.currentTimeMillis();
        int test_sum = 0;
        for (int i = 0; i < MAX_ITERATIONS; ++i)
        {
//          for (int e : array)
//          for (int e : list)          
            for (int j = 0; j < MAX_LENGTH; ++j)
            {
                int e = array[j];
//              int e = list.get(j);
                test_sum += e;
            }
        }

        long stop = System.currentTimeMillis();

        long ms = (stop - start);
        System.out.println("Time: " + ms);
    }