Java – get two different outputs from stream

I'm testing the new stream API in java-8 and want to check the results of 10000 random coinplips So far, I have:

public static void main(String[] args) {

        Random r = new Random();
        IntStream randomStream = r.ints(10000,2);

        System.out.println("Heads: " + randomStream.filter(x -> x==1).count());
        System.out.println("Tails: " + randomStream.filter(x -> x==0).count());
    }

But this threw an exception:

java.lang.IllegalStateException: stream has already been operated upon or closed

I understand why this happens, but if I can only use the stream once, how can I print the head and tail counts?

Solution

The first solution relies on the fact that the number of heads and tails of 10000 coins is calculated according to the binomial law

For this particular use case, you can use @ L_ 301_ 2 @ method

Random r = new Random();
IntStream randomStream = r.ints(10000,2);
IntSummaryStatistics stats =  randomStream.summaryStatistics();
System.out.println("Heads: "+ stats.getSum());
System.out.println("Tails: "+(stats.getCount()-stats.getSum()));

Otherwise, you can use the collect operation to create a map that maps each possible result to its number of occurrences in the stream

Map<Integer,Integer> map = randomStream
                            .collect(HashMap::new,(m,key) -> m.merge(key,1,Integer::sum),Map::putAll);
System.out.println(map); //{0=4976,1=5024}

The advantage of the last solution is that this applies to any boundary you provide for the random integer to be generated

Example:

IntStream randomStream = r.ints(10000,5);
....
map => {0=1991,1=1961,2=2048,3=1985,4=2015}