java-8

问题 I am looking at the DateTimeFormatter class and I was wondering where are the constants like "M" , "EEE" and "YY" etc are defined. More specifically there should be code like this somewhere given a ChronoField and TextStyle, it should return the DateTimeFormatter string snippet e.g. (ChronoField.MONTH_OF_YEAR, TextStyle.SHORT) should map to the string "MMM" 回答1: After some source digging, I found out that these are pre-defined in a private static final Map , called FIELD_MAP , which is a

问题 I am looking at the DateTimeFormatter class and I was wondering where are the constants like "M" , "EEE" and "YY" etc are defined. More specifically there should be code like this somewhere given a ChronoField and TextStyle, it should return the DateTimeFormatter string snippet e.g. (ChronoField.MONTH_OF_YEAR, TextStyle.SHORT) should map to the string "MMM" 回答1: After some source digging, I found out that these are pre-defined in a private static final Map , called FIELD_MAP , which is a

问题 In the following code, when catching NumberFormatException out of for iteration, the strings in appropriate form appearing in strList before the first bad one (i.e., "illegal_3" ) have been parsed successfully (i.e., "1" and "2" have been parsed as integers 1 and 2 ). public void testCaughtRuntimeExceptionOutOfIteration() { List<String> strList = Stream.of("1", "2", "illegal_3", "4", "illegal_5", "6").collect(Collectors.toList()); List<Integer> intList = new ArrayList<>(); try{ for (String

问题 Given doSomething(Function foo) { println foo(2) } Groovy: doSomething( { it*it } as Function ) Java: doSomething( (x) -> x*x ) Is there any difference between the two? 回答1: In Groovy, closures are first class citizens of type groovy.lang.Closure , whereas lambdas in Java 8 are actual instances of the default method interface they represent. This means you need to use the as keyword in Groovy (as you've shown), but alternatively, in Java you need to specify an interface, so in Groovy, you

问题 I have an object of ZonedDateTime that is constructed like this ZonedDateTime z = ZonedDateTime.of(LocalDate.now().atTime(11, 30), ZoneOffset.UTC); How can I convert it to LocalDateTime at time zone of Switzerland? Expected result should be 16 april 2018 13:30 . 回答1: How can I convert it to LocalDateTime at time zone of Switzerland? You can convert the UTC ZonedDateTime into a ZonedDateTime with the time zone of Switzerland, but maintaining the same instant in time, and then get the

问题 I have an object of ZonedDateTime that is constructed like this ZonedDateTime z = ZonedDateTime.of(LocalDate.now().atTime(11, 30), ZoneOffset.UTC); How can I convert it to LocalDateTime at time zone of Switzerland? Expected result should be 16 april 2018 13:30 . 回答1: How can I convert it to LocalDateTime at time zone of Switzerland? You can convert the UTC ZonedDateTime into a ZonedDateTime with the time zone of Switzerland, but maintaining the same instant in time, and then get the

问题 I have a method which generates an object each time I execute it, and I need to reverse the order with which I am getting them. So I thought the natural way to do it would be a Stack, since it is LIFO. However, the Java Stack does not seem to play well with the new Java 8 streaming API. If I do this: Stack<String> stack = new Stack<String>(); stack.push("A"); stack.push("B"); stack.push("C"); List<String> list = stack.stream().collect(Collectors.toList()); System.out.println("Collected: " +

问题 For developing a JavaFX application I'm using a 4.3.1 snapshot of eclipse together with JDK 8 build b116. In my workspace projects the JRE library inclusion in the build path get resetted back to Java 1.4 all the time: Unfortunately, this can only be fixed temporary (until the next eclipse restart): In the build section of my pom files I have: <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.1</version> <configuration> <source>1.8<

问题 I found this article to be very informative in comparison of old-style functions to new Java-8 lambda-functions and parallel processing. One thing I couldn't quite understand was one restriction on the lambda-functions: From page 4: 3.3 Preconditions Although lambda expressions are intended as a more con- cise alternative to AIC , they are not a complete replacement. There are several preconditions that LambdaFicator checks before refactoring an AIC into a lambda expression. These

问题 This was unexpected to me: > Clock clock = Clock.systemUTC(); > Instant.now(clock).minus(3, ChronoUnit.DAYS); java.time.Instant res4 = 2016-10-04T00:57:20.840Z > Instant.now(clock).minus(3, ChronoUnit.YEARS); java.time.temporal.UnsupportedTemporalTypeException: Unsupported unit: Years As a workaround I have to do this: > Instant.now(clock).atOffset(ZoneOffset.UTC).minus(3, ChronoUnit.YEARS).toInstant(); java.time.Instant res11 = 2013-10-07T01:02:56.361Z I am curios why Instant does not