java-8

问题 I was trying to filter Entries in HashMap using Streams API, but stuck in last method call Collectors.toMap . So, I don't have clue to implemement toMap method public void filterStudents(Map<Integer, Student> studentsMap){ HashMap<Integer, Student> filteredStudentsMap = studentsMap.entrySet().stream(). filter(s -> s.getValue().getAddress().equalsIgnoreCase("delhi")). collect(Collectors.toMap(k , v)); } public class Student { private int id; private String firstName; private String lastName;

问题 For example I have such methods: public CompletableFuture<Page> getPage(int i) { ... } public CompletableFuture<Document> getDocument(int i) { ... } public CompletableFuture<Void> parseLinks(Document doc) { ... } And my flow: List<CompletableFuture> list = IntStream .range(0, 10) .mapToObj(i -> getPage(i)) // I want method like this: .thenApplyAndSplit(CompletableFuture<Page> page -> { List<CompletableFuture<Document>> docs = page.getDocsId() .stream() .map(i -> getDocument(i)) .collect

问题 With the new java lambdas and the concept of functional interfaces, will it be possible to treat those functional interfaces as methods? interface Func { void execute(int i); } void call(Func f) { f(1); //instead of f.execute(1); } I found a lot of information about the syntax of actual lambda expressions, but nothing about this. 回答1: Your proposition What you propose has been discussed on the lambda-dev mailing list before: http://mail.openjdk.java.net/pipermail/lambda-dev/2012-February

问题 I have the Java 8 SDK and runtime, and a project that is only using Java 7 features. I was wondering whether I could set up intellij to build a Java-7-level jar, something that is definitely possible from command line? So far, I have tried simply setting the project language level to 7 as an experiment, but that is obviously insufficient and not really what I need. I have also seen this question on SO: "Intellij IDEA using java7 compiler to compile when I have configured it to use Java6", but

问题 We are developing video streaming app using JavaFx and JavaCv, While playing Stream into gridPane(8X8), we are occasionally facing splashing White Screen issue and it's continuous. Details:- new Thread(new Runnable() { @Override public void run() { frameGrabber = new FFmpegFrameGrabber(Url); frameGrabber.setVideoOption("preset","ultrafast"); frameGrabber.setOption("rtsp_transport","tcp"); frameGrabber.setOption("stimeout" , "60000"); frameGrabber.setAudioChannels(0); frameGrabber

问题 My problem in most simple expressible way: According to JavaDoc : Peek() method exists mainly to support debugging, where you want to see the elements as they flow past a certain point in a pipeline. I have a pipe of 10 Meters and at the distance of 3 and 7 meter from input head i have two markers [aka peek() ] for checking/debugging my elements. Now from Input end i am giving input of 1,2,3,4,5 . At the point x = 4 meter , i have a filter() which filters all elements less than and equal to 3

问题 public ValueA map(ValueB valueB, Date date) { Optional<ValueC> valueCOpt = find(valueB); if (valueCOpt.isPresent()) { ValueC valueC = valueCOpt.get(); // call many getters on valueC and do a lot of logic with it. return map(/*some parameters*/); } return null; } This seems quite ugly. The advantage of optionals is completely gone in here. I read that one should rather use map or flatMap instead of get . But is it really a benefit if I replace every getter like valueC.getFieldA() with

问题 Does java8 forEach method use an iterator or not really? I google it to the bone, could not find it precisely. Only the fact that it will iterate in the same order the data are. Any tips? 回答1: The default implementation of Iterable#forEach is based on a iterator. default void forEach(Consumer<? super T> action) { Objects.requireNonNull(action); for (T t : this) { action.accept(t); } } But in ArrayList is overridden to this, and not uses the iterator, it uses a for loop over its internal array

问题 So when trying to replace some legacy code using SimpleDateFormat and Date, to use java.time.DateTimeFormatter and LocalDate I ran into a problem. The two date formats are not equivalent. At this point I must say I know the two date types are not the same but the scenario I am in means I never care about the time aspect so can ignore it. public Date getDate(String value) { SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy"); try { return dateFormat.parse(value); } catch

问题 So when trying to replace some legacy code using SimpleDateFormat and Date, to use java.time.DateTimeFormatter and LocalDate I ran into a problem. The two date formats are not equivalent. At this point I must say I know the two date types are not the same but the scenario I am in means I never care about the time aspect so can ignore it. public Date getDate(String value) { SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy"); try { return dateFormat.parse(value); } catch