java-8

问题 With the release of Java 7 came the MethodHandle, which allows a user to invoke a method as if using its underlying bytecode. In particular, the MethodHandles.Lookup class provides factory methods to create method handles to access class members: The factory methods on a Lookup object correspond to all major use cases for methods, constructors, and fields. Each method handle created by a factory method is the functional equivalent of a particular bytecode behavior. Functionally, this is more

问题 With the release of Java 7 came the MethodHandle, which allows a user to invoke a method as if using its underlying bytecode. In particular, the MethodHandles.Lookup class provides factory methods to create method handles to access class members: The factory methods on a Lookup object correspond to all major use cases for methods, constructors, and fields. Each method handle created by a factory method is the functional equivalent of a particular bytecode behavior. Functionally, this is more

问题 With the release of Java 7 came the MethodHandle, which allows a user to invoke a method as if using its underlying bytecode. In particular, the MethodHandles.Lookup class provides factory methods to create method handles to access class members: The factory methods on a Lookup object correspond to all major use cases for methods, constructors, and fields. Each method handle created by a factory method is the functional equivalent of a particular bytecode behavior. Functionally, this is more

问题 Convert LocalDateTime to LocalDateTime in UTC. LocalDateTime convertToUtc(LocalDateTime date) { //do conversion } I searched over net. But did not get a solution 回答1: I personally prefer LocalDateTime.now(ZoneOffset.UTC); as it is the most readable option. 回答2: There is an even simpler way LocalDateTime.now(Clock.systemUTC()) 回答3: LocalDateTime does not contain Zone information. ZonedDatetime does. If you want to convert LocalDateTime to UTC, you need to wrap by ZonedDateTime fist. You can

问题 Convert LocalDateTime to LocalDateTime in UTC. LocalDateTime convertToUtc(LocalDateTime date) { //do conversion } I searched over net. But did not get a solution 回答1: I personally prefer LocalDateTime.now(ZoneOffset.UTC); as it is the most readable option. 回答2: There is an even simpler way LocalDateTime.now(Clock.systemUTC()) 回答3: LocalDateTime does not contain Zone information. ZonedDatetime does. If you want to convert LocalDateTime to UTC, you need to wrap by ZonedDateTime fist. You can

问题 I'm trying to use stream in java, i had a student class: @Entity @Data @AllArgsConstructor @NoArgsConstructor public class Student { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private int id; private String name; I added some students: Stream.of("John","Sophie","emilia").forEach(s->{ studentRepository.save(new Student(s)); }); The probleme is in the below code: int[] empIds = { 1, 2, 3 }; List<Student> students= Stream.of(empIds) .map(studentRepository::findById).collect

问题 I have examined the following snippet: public static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) { Map<Object, Boolean> computed = new ConcurrentHashMap<>();/*IS THIS LINE CALLED ONCE ON STREAM->FILTER NOT MATTER HOW LONG THE STREAM IS*/ return t -> {return computed.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;}; } private void test(){ final long d = Stream.of("JOHN","STEPHEN","ORTIZ","RONDON") .filter(distinctByKey(Function.identity())) .count(); System

问题 I have examined the following snippet: public static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) { Map<Object, Boolean> computed = new ConcurrentHashMap<>();/*IS THIS LINE CALLED ONCE ON STREAM->FILTER NOT MATTER HOW LONG THE STREAM IS*/ return t -> {return computed.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;}; } private void test(){ final long d = Stream.of("JOHN","STEPHEN","ORTIZ","RONDON") .filter(distinctByKey(Function.identity())) .count(); System

问题 I would like to analyse .class files and get information about which class uses which other class. jdeps is a command line tool which allows you to display some information in the console, but I would like to avoid calling an external tool and scraping the command line output. 回答1: All dependencies are recorded at a central place of a class file, the constant pool. So to efficiently process all dependencies, you need a library allowing to process the constant pool without looking at the rest

问题 I would like to analyse .class files and get information about which class uses which other class. jdeps is a command line tool which allows you to display some information in the console, but I would like to avoid calling an external tool and scraping the command line output. 回答1: All dependencies are recorded at a central place of a class file, the constant pool. So to efficiently process all dependencies, you need a library allowing to process the constant pool without looking at the rest