java-stream

问题 This question already has answers here : How to convert a Java 8 Stream to an Array? (9 answers) Java stream toArray() convert to a specific type of array (2 answers) Closed 8 months ago . I have an List<TestBuilder> testBuilders; Test has a function build of type Test I did testBuilders.stream().map(Test::build()).collect() I want to collect above in array of Test i.e Test[] I am not sure what would go in collect function 回答1: Use the terminal operation Stream::toArray which packs the

问题 We have an old-style for loop to add custom objects to ArrayList. public List<Object> generateList() { List<Object> list = new ArrayList<Object>(); for (int i = 0; i < 10; i++) { list.add(new Manager(50000, 10, "Finance Manager")); list.add(new Employee(30000, 5, "Accounts")); } return list; } Is there any way to do this by using java8? I tried to use Stream.generate(MyClass::new).limit(10); but, I am not getting the right way in java8 to achieve the above functionality. Any suggestions,

问题 We have an old-style for loop to add custom objects to ArrayList. public List<Object> generateList() { List<Object> list = new ArrayList<Object>(); for (int i = 0; i < 10; i++) { list.add(new Manager(50000, 10, "Finance Manager")); list.add(new Employee(30000, 5, "Accounts")); } return list; } Is there any way to do this by using java8? I tried to use Stream.generate(MyClass::new).limit(10); but, I am not getting the right way in java8 to achieve the above functionality. Any suggestions,

问题 this question has the reverse process in get nested List of CustomObject from JTree, including leaf I want to implement a method optimization of process, I reduced this process simple (multiplication and division) like a Tree shown. The Bottom and Bold Rectangles (the online tool don't let me change the color) represent the total multiplication between N Numerators and D Denominators of each list. Now, I was creating list of list in Java, in order to calculate the total cost of each list

问题 My problem essentially comes down to this simplified example. I have data coming back from a DB which has some duplicate information in the rows. In this example I have a list of TeamRow objects that come back from the DB. I can easily group these using Collectors.groupingBy : public class TeamRow { private int id; private String name; private String player; public TeamRow(int id, String name, String player) { this.id = id; this.name = name; this.player = player; } public int getId() {return

问题 A table about employees has following data: employee Id, employee name, their manager's Id and their team members' Id. Each employee would have multiple entries based on their team size. Say an employee with 5 other members in their team would have five rows with the employee and manager id repeated each with one team member's id. Sample table: employeeId | employeeName | managerId | teamEmployeeId | ------------------------------------------------------- 1000 | Alex | 4000 | 1101 | 1200 |

问题 Assuming I consume a Stream of entities from a source which I do not want to materialize, and I want to both transform the elements, and return some globally reduced value, what is the idiomatic way with java(8)? This is essentially trying to perform both a reduce() and a collect() . Example: class Person { public String firstname, public String lastname, public int age; } class TeamSummary { public List<String> fullnames, // firstname and lastname of all public Person oldest } public

问题 I am looking into the implementation of Streams::findLast from guava and while trying to understand it, there were a couple of things that simply I could not grasp. Here is it's implementation: public static <T> java.util.Optional<T> findLast(Stream<T> stream) { class OptionalState { boolean set = false; T value = null; void set(@Nullable T value) { set = true; this.value = value; } T get() { checkState(set); return value; } } OptionalState state = new OptionalState(); Deque<Spliterator<T>>

问题 I am trying to create one producer multiple consumers model with streams in Java8. I am reading and processing data from DB resource and I want to process them in streaming fashion way(can not read the whole resource into memory). The reading of the source has to be single threaded (the cursors is not thread safe) and reading is fast, than the processing of each data chunks which is heavy operation can run in parallel. I haven't found out how can I join (interconnect) non-parallel stream with

问题 I am trying to create one producer multiple consumers model with streams in Java8. I am reading and processing data from DB resource and I want to process them in streaming fashion way(can not read the whole resource into memory). The reading of the source has to be single threaded (the cursors is not thread safe) and reading is fast, than the processing of each data chunks which is heavy operation can run in parallel. I haven't found out how can I join (interconnect) non-parallel stream with