I would like to know the difference between CompletableFuture,Future and Observable RxJava. What I know is all are asynchronous but Future.get() blocks the thread CompletableFuture gives the callback methods RxJava Observable — similar to CompletableFuture with other benefits(not sure) For example: if client needs to make multiple service calls and when we use Futures (Java) … Read more
There are a lot of useful new things in Java 8. E.g., I can iterate with a stream over a list of objects and then sum the values from a specific field of the Object‘s instances. E.g. public class AClass { private int value; public int getValue() { return value; } } Integer sum = … Read more
I know how to “transform” a simple Java List from Y -> Z, i.e.: List<String> x; List<Integer> y = x.stream() .map(s -> Integer.parseInt(s)) .collect(Collectors.toList()); Now I’d like to do basically the same with a Map, i.e.: INPUT: { “key1” -> “41”, // “41” and “42” “key2” -> “42” // are Strings } OUTPUT: { “key1” … Read more
I am wondering why the Iterable interface does not provide the stream() and parallelStream() methods. Consider the following class: public class Hand implements Iterable<Card> { private final List<Card> list = new ArrayList<>(); private final int capacity; //… @Override public Iterator<Card> iterator() { return list.iterator(); } } It is an implementation of a Hand as you … Read more
I am trying to understand the difference between the Optional<T>.orElse() and Optional<T>.orElseGet() methods. The description for the orElse() method is “Return the value if present, otherwise return other.” While, the description for the orElseGet() method is “Return the value if present, otherwise invoke other and return the result of that invocation.” The orElseGet() method takes … Read more
Let’s say I have the following functional interface in Java 8: interface Action<T, U> { U execute(T t); } And for some cases I need an action without arguments or return type. So I write something like this: Action<Void, Void> a = () -> { System.out.println(“Do nothing!”); }; However, it gives me compile error, I … Read more
The new Java 8 stream framework and friends make for some very concise Java code, but I have come across a seemingly-simple situation that is tricky to do concisely. Consider a List<Thing> things and method Optional<Other> resolve(Thing thing). I want to map the Things to Optional<Other>s and get the first Other. The obvious solution would … Read more
I am trying to use Java 8 Streams to find elements in a LinkedList. I want to guarantee, however, that there is one and only one match to the filter criteria. Take this code: public static void main(String[] args) { LinkedList<User> users = new LinkedList<>(); users.add(new User(1, “User1”)); users.add(new User(2, “User2”)); users.add(new User(3, “User3”)); User … Read more
So I installed the beta of JDK 8 a while ago to look at some of the examples. I thought for sure by now, it’s easy to change between versions. Doing some Play development with IntelliJ. For some reason, IntelliJ is compiling with 8 even though: I have the compiler set in Preferences to use … Read more
I have an external API that returns me dates as longs, represented as milliseconds since the beginning of the Epoch. With the old style Java API, I would simply construct a Date from it with Date myDate = new Date(startDateLong) What is the equivalent in Java 8’s LocalDate/LocalDateTime classes? I am interested in converting the … Read more
