Collect

import java.util.List;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.stream.Collectors;
import java.util.stream.LongStream;
import java.util.function.Function;
import java.util.Arrays;

class Stream
{
    static List<Integer> forLoopA(List<String> strings)
    {
        List<Integer> list = new ArrayList<Integer>(strings.size());
        for (String s: strings) {
            int i = Integer.valueOf(s);
            if (i % 2 == 0) {
                list.add(i);
            }
        }
        return list;
    }

    static List<Integer> forLoopL(List<String> strings)
    {
        List<Integer> list = new LinkedList<Integer>();
        for (String s: strings) {
            int i = Integer.valueOf(s);
            if (i % 2 == 0) {
                list.add(i);
            }
        }
        return list;
    }

    static List<Integer> collect(List<String> strings)
    {
        List<Integer> list = strings.stream()
            .map(Integer::valueOf)
            .filter(i -> i % 2 == 0)
            .collect(Collectors.toCollection(ArrayList::new));
        return list;
    }

    static List<Integer> existing(List<String> strings)
    {
        List<Integer> list = new ArrayList<Integer>(strings.size());
        strings.stream()
            .map(Integer::valueOf)
            .filter(i -> i % 2 == 0)
            .forEach(n -> list.add(n));
        return list;
    }

    static void stats(long[] times, String name)
    {
        double percentiles[] = {99, 97.5, 95, 90, 80, 75, 50, 25, 20, 10, 5, 1};
        Arrays.sort(times);

        System.out.println();
        System.out.println(name + " t=" + LongStream.of(times).sum() + ":");
        System.out.println("\tmax=" + times[times.length-1]);
        for (double p: percentiles) {
            long result = 0;
            double idx = (p / 100.0) * times.length;
            if (Math.floor(idx) == idx) {
                result = (times[(int) idx - 1] + times[(int) idx]) / 2;
            } else {
                result = times[(int) Math.floor(idx)];
            }
            System.out.printf("\t.%02.0f=%d", p, result);
            System.out.println();
        }
        System.out.println("\tmin=" + times[0]);
    }

    static long[] benchmark(Function<List<String>, List<Integer>> func, List<String> list, int repeat, String name)
    {
        System.err.print(name + "...");
        long times[] = new long[repeat];
        long before = System.currentTimeMillis();
        for (int i = 0; i < repeat; ++i) {
            long start = System.currentTimeMillis();
            func.apply(list);
            long stop = System.currentTimeMillis();
            times[i] = stop - start;
        }
        long after = System.currentTimeMillis();
        System.err.println("OK (n=" + list.size() + ", m=" + repeat + ", t=" + (after - before) + ")");
        return times;
    }

    public static void main(String[] args)
    {
        final int N = 10000000;
        final int M = 50;

        List<long[]> times = new ArrayList<long[]>();

        System.err.print("Initializing numbers...");
        List<String> strings = new ArrayList<String>(N);
        for (int i = 0; i < N; ++i) {
            int n = (int) (Math.random() * 1000);
            strings.add("" + n);
        }
        System.err.println("OK");
        benchmark(Stream::forLoopA, strings, M, "Warming up");

        times.add(benchmark(Stream::forLoopA, strings, M, "forLoopA"));
        times.add(benchmark(Stream::forLoopL, strings, M, "forLoopL"));
        times.add(benchmark(Stream::existing, strings, M, "existing"));
        times.add(benchmark(Stream::collect, strings, M, "collect"));

        stats(times.get(0), "forLoopA");
        stats(times.get(1), "forLoopL");
        stats(times.get(2), "existing");
        stats(times.get(3), "collect");
    }
}