collectors

问题 Error while executing below code, Caused by: java.lang.IllegalAccessError: tried to access class com.google.common.collect.AbstractTable from class ImmutableTable.copyOf(listItemsToProcess.parallelStream() .map(item -> ProcessorInstanceProvider.getInstance() .buildImmutableTable(item)) .collect(() -> HashBasedTable.create(), HashBasedTable::putAll, HashBasedTable<Integer, String, Boolean>::putAll) ); Error in coming on - HashBasedTable::putAll Using Oracle's 1.8 jre 回答1: This is a compiler

问题 For example, if I intend to partition some elements, I could do something like: Stream.of("I", "Love", "Stack Overflow") .collect(Collectors.partitioningBy(s -> s.length() > 3)) .forEach((k, v) -> System.out.println(k + " => " + v)); which outputs: false => [I] true => [Love, Stack Overflow] But for me partioningBy is only a subcase of groupingBy . Although the former accepts a Predicate as parameter while the latter a Function , I just see a partition as a normal grouping function. So the

问题 I've already read this and this questions, but still doubt whether the observed behavior of Stream.skip was intended by JDK authors. Let's have simple input of numbers 1..20: List<Integer> input = IntStream.rangeClosed(1, 20).boxed().collect(Collectors.toList()); Now let's create a parallel stream, combine the unordered() with skip() in different ways and collect the result: System.out.println("skip-skip-unordered-toList: " + input.parallelStream().filter(x -> x > 0) .skip(1) .skip(1)

问题 This question already has answers here : What's the difference between Stream.map(…) and Collectors.mapping(…)? (2 answers) Why Stream operations is duplicated with Collectors? (2 answers) Collectors.summingInt() vs mapToInt().sum() (1 answer) Closed last month . Last time I was discovering nooks of the functional programming of Java 8 and above and I found out a static method mapping in Collectors class. We have a class Employee like: @AllArgsConstructor @Builder @Getter public class

问题 I'm new to streams but very intrigued with the possibilities. I'm trying to write a stream that does grouping, counting and summing at the same time. The data involved is actually quite simple but writing the streaming statement I need is proving challenging and I'm not seeing anything really helpful in Google searches. First, let me describe my data, then I'll show you how I've solved two-thirds of the problem. Perhaps you can tell me how to fit in the missing piece. The data is ticket sales

问题 I am new to Java 8: Streams and Collectors classes. I am reading a file whose content need to be saved in a LinkedHashMap<Integer, String> where its <keys> are the line numbers of the files and its <values> are the content at each line, respectably. Here, I want to use the Stream concept but I am not able to use Collectors.toMap to auto-increment the <keys> , which need to be saved in the LinnkedHashMap object. Instead of that I am getting exceptions. Following is the code which i am trying:

问题 In the Java library source code, the Collectors#toList method is defined like this: public static <T> Collector<T, ?, List<T>> toList() { return new CollectorImpl<>((Supplier<List<T>>) ArrayList::new, List::add, (left, right) -> { left.addAll(right); return left; }, CH_ID); } We see BinaryOperator as third parameter of CollectorImpl 's contructor, which merges two sub-results in linear time. Does it mean, that in case of frequent usage of this function by Stream#collect method, we can gain

问题 Why this code is not compile for me? I try to convert List to Map using stream and toMap option List<CountryToPaymentMethodsDisplayRules> paymentMethodDisplayRulesByCountryList = gatway.getCountryPaymentMethodsDisplayRulesByCountry(); Map<PaymentMethod, CountryToPaymentMethodsDisplayRules> countryToPaymentMethodsDisplayRulesMap = paymentMethodDisplayRulesByCountryList .stream() .collect(Collectors.toMap(type -> type.getCountryToPaymentMethodsDisplayRules().getPaymentMethod(), type -> type));

问题 I have below map of map and want to filter it based on a value. The result should be assigned back to same map. Please let know what is the best approach for this. Map<String, Map<String, Employee>> employeeMap; < dep1, <"empid11", employee11> <"empid12",employee12> dep2, <"empid21", employee21> <"empid22",employee22> > Filter: employee.getState="MI" I tried like below but i was not able to access the employee object currentMap = currentMap.entrySet().stream() **.filter(p->p.getValue()

问题 I played around with a solution using groupingBy , mapping and reducing to the following question: Elegantly create map with object fields as key/value from object stream in Java 8. Summarized the goal was to get a map with age as key and the hobbies of a person as a Set . One of the solutions I came up with (not nice, but that's not the point) had a strange behaviour. With the following list as input: List<Person> personList = Arrays.asList( new Person(/* name */ "A", /* age */ 23, /*