java-stream

问题 I am grouping and partioning a stream as follows: // Partioning Map<Boolean, List<Person>> partitioned = persons.stream(). collect(Collectors.partitioningBy(p -> p.getAge() > 20)); // Grouping Map<String, List<Person>> grouped = persons.stream() .collect(Collectors.groupingBy(p -> p.getCity())); Is there a way i can combine both of these? I tried combining both with using groupingBy inside partioningBy, but did not get the things right. Any suggestion? The expected result is the partition the

问题 I have a HashSet of Persons. A person has a firstName, lastName and age like: Person("Hans", "Man", 36) My task is to get a list of the persons who are older than 17, sort them by age and concat the firstName with the lastName like: ["Hans Man","another name", "another name"] Im just allowed to import: import java.util.stream.Stream; import java.util.stream.Collectors; import java.util.List; import java.util.ArrayList; My idea was to sort them first, map the names in separate Streams and to

问题 I have to write program which should be reading file for anagrams and show word + his anagrams. Txt files is very big, after using scanner, listOfWords size is: 25000. Output example: word anagram1 anagram2 anagram3 ... word2 anagram1 anagram2... I have code, it works but very slow: private static List<String> listOfWords = new ArrayList<String>(); private static List<ArrayList<String>> allAnagrams = new ArrayList<ArrayList<String>>(); public static void main(String[] args) throws Exception {

问题 I have to write program which should be reading file for anagrams and show word + his anagrams. Txt files is very big, after using scanner, listOfWords size is: 25000. Output example: word anagram1 anagram2 anagram3 ... word2 anagram1 anagram2... I have code, it works but very slow: private static List<String> listOfWords = new ArrayList<String>(); private static List<ArrayList<String>> allAnagrams = new ArrayList<ArrayList<String>>(); public static void main(String[] args) throws Exception {

问题 Newbie question. I have an original bean coming from the DB row-by-row as public class DataBean { private Integer employeeId; private String org; private String comments; // + Constructors, getters/setters } I need to map it to a different bean with multiple Org's grouped by Employee ID into a List. Only Orgs can be multiple for an EmployeeID; the Comments field is guaranteed to be the same. public class CustomDataBean { private Integer employeeId; private List<String> orgs; private String

问题 I have a stream function KStream<K, V>[] branch(final Predicate<? super K, ? super V>... predicates) . I wanted to create a list of predicates dynamically. Is that possible? KStream<Long, AccountMigrationEvent>[] branches = stream .map((key, event) -> enrich(key, event)) .branch(getStrategies()); [...] private List<org.apache.kafka.streams.kstream.Predicate<Long, AccountMigrationEvent>> getStrategies() { ArrayList<Predicate<Long, AccountMigrationEvent>> predicates = new ArrayList<>(); for

问题 I have two entities with one to many relationship which are joined together by composite primary keys. Since Spring Data generates wrong count distinct query for oracle database , I have SQL output with cartesian join which leads to repeating row for parent object for every row of child object. I need to find out distinct parent objects based on composite keys and then add each child object for parent in a list and set it as property of parent object I am able to find out distinct parent

问题 I am trying to learn new features in Java-9 I come to know about the dropWhile method of Stream but it is returning different values in two different scenarios. Here is my code package src.module; import java.util.stream.Collectors; import java.util.stream.Stream; import java.util.List; public class Test { public static void main(String[] args) { String s[] = new String[3]; s[0] = "Hello"; s[1] = ""; s[2] = "World"; List<String> value = Stream.of(s).dropWhile(a -> a.isEmpty()).collect

问题 I want to know how to extract a List<D> from a HashMap<E,R> considering these constraints: E is a custom class; R is a custom class containing a Set<D> of custom objects; What I have tried: I tried addressing the issue in this question. In that previous case, I had a simple Map<E,List<R>> , but in this case I have to access the R class which has the targeted Set<D> . What I want to do in the following portion of the code is to get the Elements of the Set<D> whose country names are equal to

问题 I found this code on SO to map strings to ints Arrays.stream(myarray).mapToInt(Integer::parseInt).toArray(); But how do I make it map to Integer type not the primitive int? I tried switching from Integer.parseInt to Integer.valueOf , but it seems that the mapToInt() method forces the primitive type. I have an ArrayList of arrays of Integers, so I cannot use primitive ints. 回答1: Since String and Integer are both reference types you can simply call Stream::map to transform your array. Integer[]