Java 8 List into Map
Based on Collectors documentation it’s as simple as: Map<String, Choice> result = choices.stream().collect(Collectors.toMap(Choice::getName, Function.identity()));
java-stream
Is there a concise way to iterate over a stream with indices in Java 8?
The cleanest way is to start from a stream of indices: String[] names = {“Sam”, “Pamela”, “Dave”, “Pascal”, “Erik”}; IntStream.range(0, names.length) .filter(i -> names[i].length() <= i) .mapToObj(i -> names[i]) .collect(Collectors.toList()); The resulting list contains “Erik” only. One alternative which looks more familiar when you are used to for loops would be to maintain an ad … Read more
Custom thread pool in Java 8 parallel stream
There actually is a trick how to execute a parallel operation in a specific fork-join pool. If you execute it as a task in a fork-join pool, it stays there and does not use the common one. final int parallelism = 4; ForkJoinPool forkJoinPool = null; try { forkJoinPool = new ForkJoinPool(parallelism); final List<Integer> primes … Read more
Limit a stream by a predicate
Operations takeWhile and dropWhile have been added to JDK 9. Your example code IntStream .iterate(1, n -> n + 1) .takeWhile(n -> n < 10) .forEach(System.out::println); will behave exactly as you expect it to when compiled and run under JDK 9. JDK 9 has been released. It is available for download here: JDK 9 Releases.
Zipping streams using JDK8 with lambda (java.util.stream.Streams.zip)
I needed this as well so I just took the source code from b93 and put it in a “util” class. I had to modify it slightly to work with the current API. For reference here’s the working code (take it at your own risk…): public static<A, B, C> Stream<C> zip(Stream<? extends A> a, Stream<? … Read more
Java 8 Distinct by property
Java 8 Distinct by property
How to convert to Java 8 map grouping by Map [closed]
tradeFileInstances.stream() .collect(Collectors.groupingBy(TradeFileInstance::getTradeFileConfig)); Assuming that TradeFileConfig overrides equals/hashCode
How to Map two List Of type String in third List of Object [closed]
You could do: List<Person> res = IntStream.range(0, firstName.size()) .mapToObj(i -> new Person(firstName.get(i), lastName.get(i))) .collect(Collectors.toList()); However this is assuming both List‘s are the same size This solution uses IntStream::range to generate a Stream of indices for the two List‘s
Concat parameters from object list
You are missing the map operator here. You have to add map operator to the stream processing pipeline before collecting it. Here’s how it looks. objList.stream().map(Obj::val).collect(Collectors.joining(“.”));
Compare two lists of strings using java stream
First of all, the existing solution with a loop is just fine. Simply translating it to a solution that uses streams is not an improvement. Here’s how I would do it. NB: this is not tested. // Naive version List<String> nameList1 = Arrays.asList(“Bill”, “Steve”, “Mark”); List<String> nameList2 = Arrays.asList(“Steve Jobs”, “Mark”, “Bill”); List<String> matchList = … Read more