java-stream

问题 I am trying to simulate a game board where multiple players can submit their game scores. The POJO viz. Entry.java represents an entry in the leaderboard. Note the overriden equals() method . Position is the position in the leaderboard, 1 being the user with the highest score public class Entry { private String uid; private int score; private int position; public Entry(String uid, int score) { this.uid = uid; this.score = score; } public Entry() { } public String getUid() { return uid; }

问题 I am new with Stream API and I am looking for more elegant and shortest way to fill an ArrayList with the same object using Stream API equivalent to this code: SomeObject someObject = new SomeObject(); List<SomeObject> someObjectList = new ArrayList<>(); int maxLimitValue = 70; //for example for(int i=0; i<=maxLimitValue; i++){ someObjectList.add(someObject); } I have seen many different solutions for my current task: This variant is almost what I want, but there is an auto-generation of the

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 The hashmap has two key and value pairs, they are not processed in parallel by different threads. import java.util.stream.Stream; import java.util.Map; import java.util.HashMap; class Ideone { public static void main (String[] args) throws java.lang.Exception { Map<String, Integer> map = new HashMap<>(); map.put("a", 1); map.put("b", 2); map.values().parallelStream() .peek(x -> System.out.println("processing "+x+" in "+Thread.currentThread())) .forEach(System.out::println); } } Output:

问题 This question already has answers here : How can I sort a Map according to the parameters of its values? [duplicate] (3 answers) Closed 3 years ago . I'm using the solution from this question to sort the String values in a LinkedHashMap . However the sorting simply doesn't work. Here is the code I wrote. Map<Integer, String> sortedMap = myMap.entrySet().stream() .sorted(Map.Entry.comparingByValue()) .collect(Collectors.toMap(Map.Entry<Integer, String>::getKey, Map.Entry<Integer, String>:

问题 Let's say I have a class Item like this: class Item { private long id; private BigDecimal value1; private BigDecimal value2; private BigDecimal value3; } Then I have a list with many itens, I want to know the sum of each of the values: So, I know I could do something like BigDecimal v1 = list.stream().map(Item::value1).reduce(BigDecimal.ZERO, BigDecimal::add); However, this way I would need to do the same for each value, I'd like to know if there's some way of summing each attribute into only

问题 Hi I have a List where the data looks like this [{"month":"April","day":"Friday","count":5}, {"month":"April","day":"Monday","count":6}, {"month":"April","day":"Saturday","count":2}, {"month":"April","day":"Sunday","count":1}, {"month":"April","day":"Thursday","count":7}, {"month":"April","day":"Tuesday","count":8}, {"month":"April","day":"Wednesday","count":10}, {"month":"March","day":"Friday","count":3}, {"month":"March","day":"Monday","count":2}, {"month":"March","day":"Saturday","count"

问题 Consider this code : Thread thread = new Thread(() -> tasks.parallelStream().forEach(Runnable::run)); tasks are a list of Runnables that should be executed in parallel. When we start this thread, and it begins its execution, then depending on some calculations we need to interrupt (cancel) all those tasks. Interrupting the Thread will only stop one of exections. How do we handle others? or maybe Streams should not be used that way? or you know a better solution? 回答1: You aren't actually

问题 Is there a possible identity representation of Comparator that could exist? In the search for simplifying the code in Removing overloaded method in Java, I thought about this and ended up concluding that if every comparison results in objects being equal, the order wouldn't really change making the operation an identity . Hence I ended up with (an inefficient) suggestion such as this: public static <T, G> List<G> toListOfNewType(List<T> inputList, Function<T, G> mapperFunction) { return

问题 While playing with Java parallel streams, I experienced deadlocks when some parallel operations are done within a static initializer block. When using a sequential Stream, everything works fine: import java.util.Arrays; public class Example1 { static { // displays the numbers from 1 to 10 ordered => no thread issue Arrays.asList(1,2,3,4,5,6,7,8,9,10) .forEach(s->System.out.println(s)); } public static final void main(String[] args) {} } When processing the stream in parallel, everyting work