java-stream

问题 I am writing the code using java 8 but I iterate a List and then find RestaurantOrderBook using category type. and put that List into a Map . it shows this error: Local variable itemList defined in an enclosing scope must be final or effectively final Query query = new Query(); String categ = category; query.addCriteria(Criteria.where("restaurantId").is(restaurantId)); List<RestaurantOrderBook> itemList = new ArrayList<RestaurantOrderBook>(); itemList = mongoTemplate.find(query,

问题 I have an async method with a completeablefuture result: public CompletableFuture<DogLater> asyncDogLater(String dogName){} I have a list of dogs: List<Dog> dogs; Now, I want to create a map from the dog's name to the Completeablefuture: Map<String, CompletableFuture<DogLater>> map; After checking this and this I was trying to do so: Map<String, CompletableFuture<DogLater>> completableFutures = dogs.stream() .collect( Collectors.toMap(Dog::getName, asyncDogLater(Dog::getName ))); But the

问题 I have an async method with a completeablefuture result: public CompletableFuture<DogLater> asyncDogLater(String dogName){} I have a list of dogs: List<Dog> dogs; Now, I want to create a map from the dog's name to the Completeablefuture: Map<String, CompletableFuture<DogLater>> map; After checking this and this I was trying to do so: Map<String, CompletableFuture<DogLater>> completableFutures = dogs.stream() .collect( Collectors.toMap(Dog::getName, asyncDogLater(Dog::getName ))); But the

问题 I've a a stream which I want to partition into smaller parts based on matching Id and then apply some proccessing logic on each of the part/element. class BigRequest{ String bId; List<Parts> parts; //getters and setter here } Class Parts{ String pId; String partId; //getters and setter here } I want to segregate and create a list of Parts of size 10 when the partId of different parts are same. How to use the filter or reduce or groupingBy function to compare the two elements and put them to a

问题 I'm new to using Java 8 Stream APIs but I'm looking to use it for the following problem. Say I have a POJO called InputRecord containing name , fieldA , and fieldB properties that can represent each row record of the following: name | fieldA | fieldB ---------------------- A | 100 | 1.1 A | 150 | 2.0 B | 200 | 1.5 A | 120 | 1.3 InputRecord would look like: public class InputRecord { private String name; private Integer fieldA; private BigDecimal fieldB; public String getName() { return name;

问题 Here is a code for removing only one of the max values (in this case the first one, but this is irrelevant) from the list. It is O(n) in time and O(n) in space (beyond the input). public List<Integer> removeOneOfTheMax(List<Integer> nums) { int max = Integer.MIN_VALUE; int maxIndex = -1; Iterator<Integer> it = nums.iterator(); for (int i = 0; it.hasNext(); i++) { Integer temp = it.next(); if (max < temp) { maxIndex = i; max = temp; } } nums.remove(maxIndex); return nums; } 1. What would be

问题 I have this code a: ComparisonResults comparisonResults = requestsList .stream() .map(item -> getResponse(item)) .map(item -> compareToBl(item)) .reduce(new ComparisonResults(), (result1, result2) -> { result1.addSingleResult(result2); // return result1; return new ComparisonResults(result1); }); and this code b: ComparisonResults comparisonResults = requestsList .parallelStream() .map(item -> getResponse(item)) .map(item -> compareToBl(item)) .reduce(new ComparisonResults(), (result1,

问题 Here is a query that I want to try out in MySQL SELECT A.x FROM A WHERE A.y = 'P' UNION SELECT A.x FROM A WHERE A.y = 'Q' The above is a cut-down, much simpler version of the original query that I am trying. In my original query, each SELECT statement involves multiple tables with INNER JOIN If the possible number of values in 'y' column of table 'A' that I need to query upon is 'n', then my query will involve doing 'n-1' unions on 'n' SELECT statements I know that JOOQ can do union of

问题 Having an Optional List of Optional's like: Optional<List<Optional<String>>> optionalList = Optional.of( Arrays.asList( Optional.empty(), Optional.of("ONE"), Optional.of("TWO"))); How to traverse optionalList to print out the string's ONE and TWO ? What about having an Optional Stream of Optionals? Optional<Stream<Optional<String>>> optionalStream = Optional.of( Stream.of( Optional.empty(), Optional.of("ONE"), Optional.of("TWO"))); Update: Thanks for answers, solution for optionalStream (non

问题 I want to calculate a^b , e.g. 2^30, public long pow(final int a, final int b) first I used this manner return LongStream.range(0, b).reduce(1, (acc, x) -> a * acc); // 1073741824 Got right result. Then I want to calculate it parallelly, so naturally I changed it to return LongStream.range(0, b).parallel().reduce(1, (acc, x) -> a * acc); // 32 but in this case the result is just 32 . Why? So for supporting parallel I changed it again return Collections.nCopies(b,a).parallelStream().reduce(1,