java-stream

问题 This question already has answers here : Creating an immutable list from an existing list using streams (2 answers) Closed 2 months ago . When working with Java streams, we can use a collector to produce a collection such as a stream. For example, here we make a stream of the Month enum objects, and for each one generate a String holding the localized name of the month. We collect the results into a List of type String by calling Collectors.toList(). List < String > monthNames = Arrays

问题 Can we somehow split stream into substreams with no more than N elements in Java? For example Stream<Integer> s = Stream.of(1,2,3,4,5); Stream<Stream<Integer>> separated = split(s, 2); // after that separated should contain stream(1,2), stream(3,4), stream(5) splitting by two streams solution is correct only for 2 streams, the same for N streams will be very ugly and write-only. 回答1: You can't split a Stream into 2 or more Streas s easily and directly. The only way the procedural one

问题 Can we somehow split stream into substreams with no more than N elements in Java? For example Stream<Integer> s = Stream.of(1,2,3,4,5); Stream<Stream<Integer>> separated = split(s, 2); // after that separated should contain stream(1,2), stream(3,4), stream(5) splitting by two streams solution is correct only for 2 streams, the same for N streams will be very ugly and write-only. 回答1: You can't split a Stream into 2 or more Streas s easily and directly. The only way the procedural one

问题 Context/Scenario Let's say we have an immutable object called Transaction , where transaction.getAction() would return a TransactionAction enum which can be DEPOSIT or WITHDRAW , and transaction.getAmount() would return an Integer which specify the amount of money being deposit or withdrawn. enum TransactionAction { WITHDRAW, DEPOSIT } public class Transaction { private final TransactionAction action; private final int amount; public Transaction(TransactionAction action, int amount) { this

问题 Context/Scenario Let's say we have an immutable object called Transaction , where transaction.getAction() would return a TransactionAction enum which can be DEPOSIT or WITHDRAW , and transaction.getAmount() would return an Integer which specify the amount of money being deposit or withdrawn. enum TransactionAction { WITHDRAW, DEPOSIT } public class Transaction { private final TransactionAction action; private final int amount; public Transaction(TransactionAction action, int amount) { this

问题 I have about 1,000,000 XML files and I am using XpathExpression with Java language to walk through the XML tags and get my considered data. Imagine I have about 5000 tags for name, 5000 tags for family name, 5000 tags for age, and only 1 tag for date in each file. Now I want to repeat date tag to 5000 times too. Blow code is runnable for XML files with Java programming with less than 20MB size, but I have files with more than 20MB size and it takes so many times to run and in some cases, I

问题 Collection class comes with a new method " parallelStream " in Java SDK 8. It is obvious that this new method provides a mechanism to consume collections in parallel. But, I wonder about how Java achieve this parallelism. What is the underlying mechanism? Is it simply a multithreaded execution? Or does fork/join framework (coming with Java SDK 7) step in? If the answer is neither then, how does it work and what are the advantages of it over the other two mechanisms? 回答1: Looking at the stream

问题 Collection class comes with a new method " parallelStream " in Java SDK 8. It is obvious that this new method provides a mechanism to consume collections in parallel. But, I wonder about how Java achieve this parallelism. What is the underlying mechanism? Is it simply a multithreaded execution? Or does fork/join framework (coming with Java SDK 7) step in? If the answer is neither then, how does it work and what are the advantages of it over the other two mechanisms? 回答1: Looking at the stream

问题 I was reading this book called Modern Java in Action and one part of code I could not comprehend. IntStream.iterate(0, n -> n + 4) .filter(n -> n < 100) .forEach(System.out::println); Authors says that code will not terminate. The reason is that there’s no way to know in the filter that the numbers continue to increase, so it keeps on filtering them infinitely! I did not get the reason. Could someone explain it why. 回答1: You can find the answer in javadocs of IntStream#iterate : Returns an

问题 I have a list of objects A. Each object A in this list contains list of object B and the object B contains list of Object C. The object C contains an attribute name that i want to use to filter using java 8. how to write the code below in java 8 using streams to avoid nested loop : C c1 = null; String name = "name1" for (A a: listOfAObjects) { for (B b: a.getList()) { for (C c: b.getPr()) { if (c.getName().equalsIgnoreCase(name)) { c1= c; break; } } } } 回答1: You can use two flatMap then a