The stream in Java 8 has been widely used by students in project development. Of course, everyone has also stepped on many pitfalls. Next, I will talk about the pitfalls of Collections.toMap in project use, so as to avoid being pitted again. 1. Introduction to Collectors.toMap Collectors.toMap is a collector in Java 8 that can […]
Tag: collectors
Java 8: Stream.collect and Collectors.toMap
Stream.collect: import java.util.Arrays; import java.util.IntSummaryStatistics; import java.util.List; import java.util.stream.Collectors; /** * Stream.collect */ public class Test4 {<!– –> public static void main(String[] args) {<!– –> System.out.println(“==============test1==============”); test1(); System.out.println(“==============test2==============”); test2(); System.out.println(“==============test3==============”); test3(); } /** * Stream.collect() and Collectors.joining() are used together */ private static void test3() {<!– –> List<String> list = Arrays.asList(“Ram”, “Shyam”, “Shiv”, “Mahesh”); String […]
Stream.Collectors groupingBy and partitioningBy
Stream.Collectors groupingBy and partitioningBy GroupingBy use Group based on fields in objects Mapping after grouping filter after grouping Get the maximum after grouping Custom grouping sum after grouping Statistics after grouping Multiple grouping PartitioningBy use Simple to use Overview: When we encounter a collection, we need to proceed based on a certain field Group or […]
Building Observability with OpenTelemetry 04 – Collectors
In a previous blog post, we discussed how to export in-process telemetry using the SDK and the Link Tracing Producer. Although there are many types of exporters to choose from, one common goal is to export data to OpenTelemetry Collector. This article will take a deep dive into the Collector and how to use it. […]
zjzcyList.stream().map(Pb_zjzcy::getZjid).collect(Collectors.toList()); explain
zjzcyList.stream().map(Pb_zjzcy::getZjid).collect(Collectors.toList()); explain This code uses Java 8’s stream processing (Stream) to operate on a list (zjzcyList) that stores objects, and finally returns a new list that contains the Zjid attribute of each object in the list. The specific operation is as follows: Use the stream() method to convert zjzcyList into a Stream (Stream) object, so […]
Components of the JVM, how automatic garbage collection works, the generational garbage collection process, types of garbage collectors available
Detailed jvm model diagram https://www.processon.com/diagraming/64c8aa11c07d99075d934311 Official URL https://www.oracle.com/webfolder/technetwork/tutorials/obe/java/gc01/index.html Related concepts The young generation is where all new objects are allocated and aged. When the young generation is full, this will lead to minor garbage collection, and minor gc will recycle a lot of free objects. The free young generation is collected very quickly. Some of […]
Stream – Collectors.groupingBy implements grouping, and each grouping is also sorted
Article directory foreword 1. Advanced usage of groupingBy Second, group first, then sort Summarize Foreword It has been recorded before: three common ways of stream (toMap, groupingBy, findFirst). Here we continue to record several advanced usages of groupingBy. In my opinion, the most divisive thing is: realize grouping, and each group is also sorted Here […]
Ordered collections use Collectors.groupingBy() or Collectors.toMap() to output out-of-order problems
Collectors.groupingBy() output out of order Scene For example, group the ordered order list (in descending order of creation time) by order number, and return the order list information Using Collectors.groupingBy, the data finally returned to the front-end is not in the same order as the ordered order list before grouping, resulting in out-of-order output. import […]
Ordered collections use Collectors.groupingBy() or Collectors.toMap() to output out-of-order problems
Collectors.groupingBy() output out of order Scene For example, group the ordered order list (in descending order of creation time) by order number, and return the order list information Using Collectors.groupingBy, the data finally returned to the front end is not in the same order as the ordered order list before grouping, resulting in out-of-order output. […]
stream collectors
As for the cause, I was new to the company and saw an interesting piece of code. public final class MyCollectors { private MyCollectors() { } static final Set<Collector.Characteristics> CH_ID = Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.IDENTITY_FINISH)); static class CollectorImpl<T, A, R> implements Collector<T, A, R> { private final Supplier<A> supplier; private final BiConsumer<A, T> accumulator; private final BinaryOperator<A> combiner; […]