java-8

问题 geniuses! I'm practicing Java 8. So if I do something like this: Files.walk(Paths.get(corpusPathStr)) .filter(path -> path.toFile().isFile()) .forEach(path -> { try { Files.lines(path) .forEach(...); } catch (IOException e) { e.printStackTrace(); } }); I got FileSystemException error. If I open a file under forEach, may too many files be opened? Or are there other reasons causing FileSystemException (Too many open files)? Thanks for your help in advance! 回答1: Use try(Stream<Path> stream =

问题 geniuses! I'm practicing Java 8. So if I do something like this: Files.walk(Paths.get(corpusPathStr)) .filter(path -> path.toFile().isFile()) .forEach(path -> { try { Files.lines(path) .forEach(...); } catch (IOException e) { e.printStackTrace(); } }); I got FileSystemException error. If I open a file under forEach, may too many files be opened? Or are there other reasons causing FileSystemException (Too many open files)? Thanks for your help in advance! 回答1: Use try(Stream<Path> stream =

问题 I have the following qustion: How can I convert the following code snipped to Java 8 lambda style? List<String> tmpAdresses = new ArrayList<String>(); for (User user : users) { tmpAdresses.add(user.getAdress()); } Have no idea and started with the following: List<String> tmpAdresses = users.stream().map((User user) -> user.getAdress()); 回答1: You need to collect your stream into a List: List<String> adresses = users.stream() .map(User::getAdress) .collect(Collectors.toList()); For more

问题 I have the following qustion: How can I convert the following code snipped to Java 8 lambda style? List<String> tmpAdresses = new ArrayList<String>(); for (User user : users) { tmpAdresses.add(user.getAdress()); } Have no idea and started with the following: List<String> tmpAdresses = users.stream().map((User user) -> user.getAdress()); 回答1: You need to collect your stream into a List: List<String> adresses = users.stream() .map(User::getAdress) .collect(Collectors.toList()); For more

问题 As a primitive version of Optional*, Java 1.8 provides OptionalInt, OptionalLong and OptionalDouble. But I cannot find the equivalent OptionalBoolean class. Are there any technical reasons against having an OptionalBoolean ? * An Optional may or may not have the presence of a value, is used as an alternative to null . 回答1: This quote explains the considerations behind having primitive streams. I'm assuming the same applied to primitive Optionals. In short, primitive streams (and probably

问题 Could you please shed some light on how to obtain correct epoch time in milliseconds for a default system timezone and given timezone. Given 1. TimeZone: GMT+3 2. The following code snippet: import java.time.*; public class Main { public static void main(String[] args) { System.out.println(LocalDateTime .now() .atZone(ZoneOffset.UTC) .toInstant() .toEpochMilli() ); System.out.println(LocalDateTime .now() .atZone(ZoneOffset.of("+3")) .toInstant() .toEpochMilli() ); System.out.println(System

问题 I was playing with Java8 Lambda last night and I was wondering if it is possible to retrieve the Lambda expression at runtime. In short and as far as I understood, Lambda expression are converted into (static) methods at runtime and then called using InvokeDynamics. Let's take an example like this: people.filter(person -> person.getAge() >= minAge); where filter would be a custom method taking a Predicate<T> as a parameter. Inside this filter method, how could I retrieve the argument in a

问题 I have a list of objects to be added in a bag and bags capacity is 100 qty The Object and Bag look like below public class MyObject{ String id; int qty; } public class MyBag{ String id; int qty; } Is there any way to split MyObject in multiple MyBags grouping on the qty limit using Java 8 streams For example: myObjects are [myObject1:{id1, 150}, myObject2:{id2, 30}, myObject3:{id3, 150}] Since bag has a capacity of 100. Bags should be grouped as [ bag1:[{id1, 100}], bag2:[{id1, 50},{id2, 30},

问题 I have a list of objects to be added in a bag and bags capacity is 100 qty The Object and Bag look like below public class MyObject{ String id; int qty; } public class MyBag{ String id; int qty; } Is there any way to split MyObject in multiple MyBags grouping on the qty limit using Java 8 streams For example: myObjects are [myObject1:{id1, 150}, myObject2:{id2, 30}, myObject3:{id3, 150}] Since bag has a capacity of 100. Bags should be grouped as [ bag1:[{id1, 100}], bag2:[{id1, 50},{id2, 30},

问题 I have a list of objects to be added in a bag and bags capacity is 100 qty The Object and Bag look like below public class MyObject{ String id; int qty; } public class MyBag{ String id; int qty; } Is there any way to split MyObject in multiple MyBags grouping on the qty limit using Java 8 streams For example: myObjects are [myObject1:{id1, 150}, myObject2:{id2, 30}, myObject3:{id3, 150}] Since bag has a capacity of 100. Bags should be grouped as [ bag1:[{id1, 100}], bag2:[{id1, 50},{id2, 30},