java-8

问题 I have a container running a Spring Boot microservice. I am using openjdk version "1.8.0_212" under OpenJDK Runtime Environment (IcedTea 3.12.0) (Alpine 8.212.04-r0) When I use - XX:+PrintFlagsFinal flag and print the JVM parameters I expected to see -XX:+UseParallelGC as true But to my surprise none of the 4 collectors (-XX:+UseSerialGC,-XX:+UseParallelGC,-XX:+UseConcMarkSweepGC,–XX:+UseG1GC) were active. Shown below is my dockerfile: FROM openjdk:8-jdk-alpine ADD ./demo-0.0.1-SNAPSHOT.jar

问题 I am new to Java 8. I have a list of custom objects of type A, where A is like below: class A { int id; String name; } I would like to determine if all the objects in that list have same name. I can do it by iterating over the list and capturing previous and current value of names. In that context, I found How to count number of custom objects in list which have same value for one of its attribute. But is there any better way to do the same in java 8 using stream? 回答1: One way is to get the

问题 I'm trying to use Java 8's java.time.format.DateTimeFormatter to parse a formatted string into a java.time.LocalTime object. However, I'm running into some problems with parsing some input strings. When my input string has "AM" it parses correctly, but when my string has "PM" it throws an exception. Here's a simple example: import java.time.LocalTime; import java.time.format.DateTimeFormatter; public class FormatterExample { private static final DateTimeFormatter timeFormatter =

问题 I am using spark-sql-2.4.1v in my project with java8. I need to calculate the quantiles on the some of the (calculated) columns (i.e. con_dist_1 , con_dist_2 ) of below given dataframe df : +----+---------+-------------+----------+-----------+ | id| date| revenue |con_dist_1| con_dist_2| +----+---------+-------------+----------+-----------+ | 10|1/15/2018| 0.010680705| 6|0.019875458| | 10|1/15/2018| 0.006628853| 4|0.816039063| | 10|1/15/2018| 0.01378215| 4|0.082049528| | 10|1/15/2018| 0

问题 I am using spark-sql-2.4.1v in my project with java8. I need to calculate the quantiles on the some of the (calculated) columns (i.e. con_dist_1 , con_dist_2 ) of below given dataframe df : +----+---------+-------------+----------+-----------+ | id| date| revenue |con_dist_1| con_dist_2| +----+---------+-------------+----------+-----------+ | 10|1/15/2018| 0.010680705| 6|0.019875458| | 10|1/15/2018| 0.006628853| 4|0.816039063| | 10|1/15/2018| 0.01378215| 4|0.082049528| | 10|1/15/2018| 0

问题 Why i am getting this error while using GrantedAuthority . 1 CustomUserDetails class. public class CustomUserDetails extends User implements UserDetails { public CustomUserDetails(final User user) { super(user); } @Override public Collection<? extends GrantedAuthority> getAuthorities() { return getRoles().stream().map( r -> { new SimpleGrantedAuthority(r.getRole().name()); } ).collect(Collectors.toList()); } Role class. @Entity(name = "ROLE") public class Role { @Id @Column(name = "ROLE_ID")

问题 I am surprised to discover that somehow, recently, jstack stopped working on newer JDK 8. I am not sure around which release this happened but I do get: 36649: Unable to open socket file: target process not responding or HotSpot VM not loaded The -F option can be used when the target process is not responding ps -Af|grep 36649 conflue+ 36649 1 62 08:14 ? 00:48:28 /usr/lib/jvm/java-8-oracle/bin/java -Djava.util.logging.config.file=/opt/atlassian/confluence/conf/logging.properties -Djava.util

问题 I want to annotate a fully qualified class name with @Nullable -annotation (from the Java Checker Framework), e.g.: class Demo { private transient @Nullable org.apache.lucene.search.Query cached_results; // ... } However this results in the error: scoping construct cannot be annotated with type-use annotation: @checkers.nullness.quals.Nullable How can I annotate fully qualified class names? 回答1: The Java language specification (draft for version 8) §8.3 specifies a "UnannClassType" as

问题 I have a list of ScheduleContainer objects and in the stream each element should be casted to type ScheduleIntervalContainer . Is there a way of doing this? final List<ScheduleContainer> scheduleIntervalContainersReducedOfSameTimes final List<List<ScheduleContainer>> scheduleIntervalContainerOfCurrentDay = new ArrayList<>( scheduleIntervalContainersReducedOfSameTimes.stream() .sorted(Comparator.comparing(ScheduleIntervalContainer::getStartDate).reversed()) .filter(s -> s.getStartDate()

问题 Learning java 8 default methods . This link like any other resource on internet says In ‘the strictest sense’, Default methods are a step backwards because they allow you to ‘pollute’ your interfaces with code. But they provide the most elegant and practical way to allow backwards compatibility. It made it much easier for Oracle to update all the Collections classes and for you to retrofit your existing code for Lambda. My understanding is that java 8 dev/designers provided the default method