java-8

问题 I really have difficulties to understand how the ObservableList object is working in JavaFX. I want to monitor if an object in the List has been modified. So far, I only see that I can monitor if the List , as an entity itself, has been modified... but not the objects within the List : ObservableList<Stuff> myList = FXCollections.<Stuff>observableArrayList(); myList.add(someStuff); myList.addListener((ListChangeListener.Change<? extends Stuff> change) -> { while(change.next()){ if(change

问题 Java8 introduced those nice methods getOrDefault() and putIfAbsent() , allowing to write code like: Map<Foo, List<Bar>> itemsByFoo = ... List<Bar> bars = itemsByFoo.getOrDefault(key, new ArrayList<>()); bars.add(someNewBar); Now I am wondering if there are good factual reasons to either do: itemsByFoo.put(key, bars); or itemsByFoo.putIfAbsent(key, bars); Both would work: option 1 might do a lot of unnecessary "put" calls when adding elements to lists happens often option2 might do a lot of

问题 I am trying to install java 8 through oracle-java8-installer on a debian:jessie docker container. The following is my Dockerfile: FROM debian:jessie ENV JAVA_VERSION 1.8.0 RUN echo "deb http://ppa.launchpad.net/webupd8team/java/ubuntu trusty main" > /etc/apt/sources.list.d/webupd8team-java.list RUN echo "deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu trusty main" >> /etc/apt/sources.list.d/webupd8team-java.list RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys

问题 To sort it int ascending order I can use: myMap.entrySet().stream() .sorted(Map.Entry.comparingByValue()) .collect(Collectors.toMap(Entry::getKey, Entry::getValue)); How can I do it in decreasing order? 回答1: To sort in reverse order, pass Comparator.reverseOrder() as parameter to comparingByValue . To get a LinkedHashMap , you must specifically request one with the 4-argument toMap() . If you don't specify what kind of a map you want, you will get whatever the default is, which currently

问题 I've created method whih numerating each character of alphabet. I'm learning streams(functional programming) and try to use them as often as possible, but I don't know how to do it in this case: private Map<Character, Integer> numerateAlphabet(List<Character> alphabet) { Map<Character, Integer> m = new HashMap<>(); for (int i = 0; i < alphabet.size(); i++) m.put(alphabet.get(i), i); return m; } So, how to rewrite it using streams of Java 8? 回答1: Avoid stateful index counters like the

问题 This question already has answers here : Java 8 Lambda function that throws exception? (24 answers) Closed 4 years ago . Given this java 8 code public Server send(String message) { sessions.parallelStream() .map(Session::getBasicRemote) .forEach(basic -> { try { basic.sendText(message); } catch (IOException e) { e.printStackTrace(); } }); return this; } how do we properly make this IOException be delegated up the stack of the method call? (in nutshell how to make this method throw this

问题 This question already has answers here : Java 8 Lambda function that throws exception? (24 answers) Closed 4 years ago . Given this java 8 code public Server send(String message) { sessions.parallelStream() .map(Session::getBasicRemote) .forEach(basic -> { try { basic.sendText(message); } catch (IOException e) { e.printStackTrace(); } }); return this; } how do we properly make this IOException be delegated up the stack of the method call? (in nutshell how to make this method throw this

问题 I am posting my query after having searched in this forum & google, but was unable to resolve the same. eg: Link1 Link2 Link3 I am trying to filter List 2 (multi column) based on the values in List 1. List1: - [Datsun] - [Volvo] - [BMW] - [Mercedes] List2: - [1-Jun-1995, Audi, 25.3, 500.4, 300] - [7-Apr-1996, BMW, 35.3, 250.2, 500] - [3-May-1996, Porsche, 45.3, 750.8, 200] - [2-Nov-1998, Volvo, 75.3, 150.2, 100] - [7-Dec-1999, BMW, 95.3, 850.2, 900] expected o/p: - [7-Apr-1996, BMW, 35.3, 250

问题 How could I do the following with Java Streams? Let's say I have the following classes: class Foo { Bar b; } class Bar { String id; String date; } I have a List<Foo> and I want to convert it to a Map <Foo.b.id, Map<Foo.b.date, Foo> . I.e: group first by the Foo.b.id and then by Foo.b.date . I'm struggling with the following 2-step approach, but the second one doesn't even compile: Map<String, List<Foo>> groupById = myList .stream() .collect( Collectors.groupingBy( foo -> foo.getBar().getId()

问题 Suppose I have a list like this : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] Is it possible to use a Java 8 stream to take every second element from this list to obtain the following? [1, 3, 5, 7, 9] Or maybe even every third element? [1, 4, 7, 10] Basically, I'm looking for a function to take every nth element of a stream: List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); List<Integer> list2 = list.stream().takenth(3).collect(Collectors.toList()); System.out.println(list2); // => [1, 4