java-stream

This question already has answers here : Java 8's streams: why parallel stream is slower? (4 answers) How do I write a correct micro-benchmark in Java? (11 answers) Why is parallel stream slower? (3 answers) Closed 2 years ago . I was attempting to demonstrate to a Java novice streams and such. He said he had read that streams can be slower than for loops for primitive types. So, I set immediately to prove that wrong! What I got was a shock! The for-loop and the serial stream run roughly the same, but the parallel stream is consistently and dramatically slower. Can someone explain why? @Test

I asked this question about doing the same thing with 1D lists, figuring that it would be easy to apply the answers to 2D lists, but it was not. Basing my code off of Holger's answer, I came up with this solution: //list is of type ArrayList<List<Integer>> list.stream() .map(l -> Stream.concat( l.subList(0, l.size() - 1).stream().map(i -> i - 2), Stream.of(l.get(l.size() - 1)).collect(Collectors.toList()) )) .collect(Collectors.toList()); I get the compile-time error Cannot infer type argument(s) for <R> map(Function<? super T,? extends R>) , however, when I try this. How is can I perform this

Here is a query that I want to try out in MySQL SELECT A.x FROM A WHERE A.y = 'P' UNION SELECT A.x FROM A WHERE A.y = 'Q' The above is a cut-down, much simpler version of the original query that I am trying. In my original query, each SELECT statement involves multiple tables with INNER JOIN If the possible number of values in 'y' column of table 'A' that I need to query upon is 'n', then my query will involve doing 'n-1' unions on 'n' SELECT statements I know that JOOQ can do union of multiple SELECT statements. But is there a good way to do this post Java 8 style? maybe using Steam.collect()

I have a User class with name, type and age and then a long list of these users are my input List<User> users = db.getUsers(); . I am trying to create a set of all unique users from this, but the problem is I am looking for sorting them based on the age also. I have currently used- Set<User> set = users.stream().collect(Collectors.toSet()); How to sort this set at the same time as well, any idea? It doesn't make sense to speak of order within a non sorted set. You should be using something like TreeSet if you want a set ordered by age. Comparator<User> byAge = Comparator.comparingInt(User:

This question is an extension to the post: Java 8 groupingby with returning multiple field . For the same problem, how do you return a list of Customer ? For example, it should return: Customer("A",4500,6500) Customer("B",3000,3500) Customer("C",4000,4500) @Pankaj Singhal's post is the right idea if you want a Map<String, Customer> as the result set +1. However, I would extract the merging logic into its own function e.g. in the Customer class you would have a function as such: public static Customer merge(Customer first, Customer second) { first.setTotal(first.getTotal() + second.getTotal());

If the Stream s below has at least n elements, what are the situations where the stream sLimit may have less than n elements, if any? Stream sLimit = s.limit(n); Reason for the question: in this answer , I read that: Despite the appearances, using limit(10) doesn't necessarily result in a SIZED stream with exactly 10 elements -- it might have fewer. I think Holger's and Sotirios' answers are accurate, but inasmuch as I'm the guy who made the statement, I guess I should explain myself. I'm mainly talking about spliterator characteristics , in particular the SIZED characteristic. This is