Java parallelStream not showing correct result

I was doing some performance evaluation of Java aggeragate operations to iterate over collections. I was doing an evaluation of performance stream and parallelStream. But I found that the output of parallelStream is wrong most of the times. For example in the following code i got wrong output from parallelStream more than 80% of the time:

    public class ParallelStreamPerformance {
    static int totaleven = 0;
    public static void main(String[] args) {
        List randomList = new ArrayList<>();
        Random rnd = new Random();
        for(int i = 0 ;i < 1000;i++) {
            int r = rnd.nextInt(500000);
            randomList.add(r);
        }


        long s1 = System.currentTimeMillis();

        randomList.stream().filter(e -> e%2 ==0).forEach(e -> count());
        System.out.println("Even: "+totaleven);
        long e1 = System.currentTimeMillis();
        System.out.println(e1 - s1);

        totaleven = 0;
        long s2 = System.currentTimeMillis();


        randomList.parallelStream().filter(e -> e%2 ==0).forEach(e -> count());
        System.out.println("Even: "+totaleven);
        long e2 = System.currentTimeMillis();
        System.out.println(e2 - s2);
    }
    public static void count() {
        totaleven++;
    }
}

My question is: Am I using parallelStream in a wrong way? Is there any way to ensure the correctness of parallelStream.
Thanks

Answer

I think your code having issue with count() method. As parallelStream will try to perform task concurrently. This method should be synchronized or you can make totaleven as Atomtic Integer. Hope it helps.