java-8

Why is the max recursion depth I can reach non-deterministic?

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The observed behavior is affected by the HotSpot optimizer, however it is not the only cause. When I run the following code public static void main(String[] argv) { System.out.println(System.getProperty(“java.version”)); System.out.println(countDepth()); System.out.println(countDepth()); System.out.println(countDepth()); System.out.println(countDepth()); System.out.println(countDepth()); System.out.println(countDepth()); System.out.println(countDepth()); } static int countDepth() { try { return 1+countDepth(); } catch(StackOverflowError err) { return 0; } } with JIT … Read more

Default methods and interfaces extending other interfaces

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This is exactly addressed by the JLS in 15.12.3. “Compile-Time Step 3: Is the Chosen Method Appropriate?”. If the form is TypeName . super . [TypeArguments] Identifier, then: […] If TypeName denotes an interface, let T be the type declaration immediately enclosing the method invocation. A compile-time error occurs if there exists a method, distinct … Read more

Java 8 Consumer/Function Lambda Ambiguity

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This line is definitely ambiguous: doStuff(getPattern(x -> String.valueOf(x))); Reread this from the linked JLS chapter: A lambda expression (§15.27) is potentially compatible with a functional interface type (§9.8) if all of the following are true: The arity of the target type’s function type is the same as the arity of the lambda expression. If the … Read more

Chain of Map method references

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Nope, these are the two ways of doing it. Anything else would end up being only less clear. But, since you asked, here are some options. static<T,U,R> Function<T,R> chain( Function<? super T, ? extends U> f1, Function<? super U, ? extends R> f2) { return t -> f2.apply(f1.apply(t)); } stream.map(chain(Status::getUser, User::getId)) Or static<T,R> Function<T,R> func(Function<T,R> … Read more

ExecutorService vs CompletableFuture

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Functionally, the two approaches are more or less the same: you submit your tasks for execution; you don’t wait for the result. Technically, however, there are some subtle differences: In the second approach, you didn’t specify an executor, so it will use the common ForkJoinPool. You would have to pass an executor as second argument … Read more

Show progress of Java 8 stream processing

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First of all, Streams are not meant to achieve these kind of tasks (as opposed to a classic data structure). If you know already how many elements your stream will be processing you might go with the following option, which is, I repeat, not the goal of streams. Stream<MyData> myStream = readData(); final AtomicInteger loader … Read more

How to perform Stream functions on an Iterable? [duplicate]

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My similar question got marked as duplicate, but here is the helper methods I’ve used to avoid some of the boilerplate: public static <T> Stream<T> stream(Iterable<T> in) { return StreamSupport.stream(in.spliterator(), false); } public static <T> Stream<T> parallelStream(Iterable<T> in) { return StreamSupport.stream(in.spliterator(), true); }

Empty methods noticeably slower in Java 11 than Java 8

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You are measuring empty benchmarks, not empty methods. In other words, measuring the minimal infrastructure code that handles the benchmark itself. This is easy to dissect, because you’d expect only a few instructions on the hot path. JMH’s -prof perfasm or -prof xperfasm would give you those hottest instructions in seconds. I think the effect … Read more