Sum of subtractions using the Java Stream API

everyone. I've faced a task, that looked pretty simple to me, but I spend like 4 hours and left with nothing. So, let's assume we have simple list of integers like [1, 2, 3, 4, 5] I want to get sum of subtractions for each element - for this list, it

Why a ForkJoinPool parallelism doubles my exception?

assuming I have the code like as below: Future<Object> executeBy(ExecutorService executor) { return executor.submit(() -> { throw new IllegalStateException(); }); } there is no problem when using ForkJoinPool#commonPool, but when I using a parall

Which syntax is java8 and where can I read more?

How do you put multiple method calls (e.g 'get' in the below case) in a block? package Routes; import org.jooby.mvc.Path; public class UserRoutes extends BaseRoutes { { get("/users", (req, resp) -> { resp.send("Uses index"); }); get

Are parallel and forkjoinpool flows safe to use in production?

We developed an API call which uses Java8 parallel streams and we have got very good performance, almost double compared to sequential processing when doing stress tests. I know it depends on the use case, but I am using it for crypto operations, so

How to test Java 8 in Travis CI?

I am trying to run a Travis CI test. Like this: language: java jdk: oraclejdk8 sudo: false script: mvn test It should be really simple... but I get this erro: diamond operator is not supported in -source 1.5 (use -source 7 or higher to enable diamond

Java TimeZoneOffset Time Conversion

Using Jdk8. I am trying to convert time actually just hours of the day (like 1130) into DateTime. I am trying it 2 ways as below none of them work correctly. 1130 gets converted into 11:00 and another 3:00 none of them are correct. Is there also a 3r

Mathematical operation inherent in Java

I'm writing essentially a small calaculator where you input two numbers, an operand like "+, -, *, /" etc and it'll preform that function. My initial thoughts have been to just have the variables get entered by the user, than just have them comp

Java 8 Repeatable Annotation

Trying to figure out how to get along with Java 8 Repeatable annotations support. Following : https://blog.idrsolutions.com/2015/03/java-8-repeating-annotation-explained-in-5-minutes/ it works flawlessly. But if I'm modifying the example and add just

java.lang.IllegalStateException: endPosTable already defined

Trying to build an alexa (amazon:echo) skills set. At the same time, trying to use this experience as a learning testbed for dependency injection through dagger 2. However, building the package using maven-2 cmd: mvn assembly:assembly -DdescriptorId=

Java 8: How to derive a ZoneId from ZoneOffset

I was reading the API for the ZoneId class. It states that there are three tipes of ID: derived from ZoneOffset offset-style IDs with some form of prefix. Examples: ZoneId.of("GMT+2"); ZoneId.of("UTC"); ZoneId.of("UT+01:00");

Why does Stream.allMatch () return true for an empty stream?

My colleague and I had a bug that was due to our assumption that an empty stream calling allMatch() would return false. if (myItems.allMatch(i -> i.isValid()) { //do something } Of course, it is kind of our fault for assuming and not reading document

Java 8: Lambda Card Expression

I have a Map<String, List<Object>> multiFieldMap and I need to itereate over its value set and add the value to multiFieldsList as below public List<Object> fetchMultiFieldsList() { List<Object> multiFieldsList = new ArrayList<O

Java8 Provider who is an optional consumer

I can explain this one only with the example. We have the main class, AppServer. It holds also several application-wide components. AppServer app = new AppServer(config, ...); Now we need to provide a supplier that will act as a factory for some Foo

What is the purpose of partitioningBy

For example, if I intend to partition some elements, I could do something like: Stream.of("I", "Love", "Stack Overflow") .collect(Collectors.partitioningBy(s -> s.length() > 3)) .forEach((k, v) -> System.out.println(

Why String.chars () a stream of ints in Java 8?

In Java 8, there is a new method String.chars() which returns a stream of ints (IntStream) that represent the character codes. I guess many people would expect a stream of chars here instead. What was the motivation to design the API this way?As othe

Call the constructor on a double board via Streams

I am wondering if the following is possible with Java 8, for: Patch[][] patches = new Patch[width][depth]; I want to call the constructor using Streams, I know there is Arrays.stream(patches) which would give me a Stream<Patch[]>, so unfortunately I