java-8

问题 This question already has answers here : How will Java lambda functions be compiled? (3 answers) Closed 5 years ago . I have read this article today regarding lambdas: http://www.infoq.com/articles/Java-8-Lambdas-A-Peek-Under-the-Hood The article suggests, that lambdas are not implemented as anon inner classes (due to performance). It gives an example that a lambda expression can be compiled as a (static) method of class. I have tried a very simple snippet: private void run() { System.out

问题 With Java-8 I can easily treat a String (or any CharSequence ) as an IntStream using either the chars or the codePoints method. IntStream chars = "Hello world.".codePoints(); I can then manipulate the contents of the stream IntStream stars = chars.map(c -> c == ' ' ? ' ': '*'); I have been hunting for a tidy way to print the results and I cant even find a simple way. How do I put this stream of int s back into a form that can be printed like I can a String . From the above stars I hope to

问题 In Java 8, I want to convert a datetime from UTC to ACST (UTC+9:30). input -> 2014-09-14T17:00:00+00:00 output-> 2014-09-15 02:30:00 String isoDateTime = "2014-09-14T17:00:00+00:00"; LocalDateTime fromIsoDate = LocalDateTime.parse(isoDateTime, DateTimeFormatter.ISO_OFFSET_DATE_TIME); ZoneOffset offset = ZoneOffset.of("+09:30"); OffsetDateTime acst = OffsetDateTime.of(fromIsoDate, offset); System.out.println(acst.toString()); // 2014-09-14T17:00+09:30 System.out.println(acst.format

问题 I proceed java 8 learning. I have found interesting behaviour: lets see code sample: // identity value and accumulator and combiner Integer summaryAge = Person.getPersons().stream() //.parallel() //will return surprising result .reduce(1, (intermediateResult, p) -> intermediateResult + p.age, (ir1, ir2) -> ir1 + ir2); System.out.println(summaryAge); and model class: public class Person { String name; Integer age; ///... public static Collection<Person> getPersons() { List<Person> persons =

问题 I m using Java 8 for grouping by data. But results obtained are not in order formed. Map<GroupingKey, List<Object>> groupedResult = null; if (!CollectionUtils.isEmpty(groupByColumns)) { Map<String, Object> mapArr[] = new LinkedHashMap[mapList.size()]; if (!CollectionUtils.isEmpty(mapList)) { int count = 0; for (LinkedHashMap<String, Object> map : mapList) { mapArr[count++] = map; } } Stream<Map<String, Object>> people = Stream.of(mapArr); groupedResult = people .collect(Collectors.groupingBy

问题 I m using Java 8 for grouping by data. But results obtained are not in order formed. Map<GroupingKey, List<Object>> groupedResult = null; if (!CollectionUtils.isEmpty(groupByColumns)) { Map<String, Object> mapArr[] = new LinkedHashMap[mapList.size()]; if (!CollectionUtils.isEmpty(mapList)) { int count = 0; for (LinkedHashMap<String, Object> map : mapList) { mapArr[count++] = map; } } Stream<Map<String, Object>> people = Stream.of(mapArr); groupedResult = people .collect(Collectors.groupingBy

问题 In Java 8, methods can be created as Lambda expressions and can be passed by reference (with a little work under the hood). There are plenty of examples online with lambdas being created and used with methods, but no examples of how to make a method taking a lambda as a parameter. What is the syntax for that? MyClass.method((a, b) -> a+b); class MyClass{ //How do I define this method? static int method(Lambda l){ return l(5, 10); } } 回答1: Lambdas are purely a call-site construct: the

问题 Is there a better way to count int occurrences with Java8 int[] monthCounter = new int[12]; persons.stream().forEach(person -> monthCounter[person.getBirthday().getMonthValue() - 1]++); 回答1: Try: Map<Integer, Long> counters = persons.stream() .collect(Collectors.groupingBy(p -> p.getBirthday().getMonthValue(), Collectors.counting())); 回答2: With Eclipse Collections (formerly GS Collections), you can make use of a data structure called Bag that can hold the number of occurrences of each element

问题 I'm playing with the new lambda features in Java 8, and found that the practices offered by Java 8 are really useful. However, I'm wondering is there a good way to make a work-around for the following scenario. Suppose you have an object pool wrapper that requires some kind of a factory to fill the object pool, for example (using java.lang.functions.Factory ): public class JdbcConnectionPool extends ObjectPool<Connection> { public ConnectionPool(int maxConnections, String url) { super(new

问题 I'm playing with the new lambda features in Java 8, and found that the practices offered by Java 8 are really useful. However, I'm wondering is there a good way to make a work-around for the following scenario. Suppose you have an object pool wrapper that requires some kind of a factory to fill the object pool, for example (using java.lang.functions.Factory ): public class JdbcConnectionPool extends ObjectPool<Connection> { public ConnectionPool(int maxConnections, String url) { super(new