自定义实现Collector,和对Characteristics的实验

import java.util.*;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;import static java.util.stream.Collector.Characteristics.*;/*** input Set output Map<String, String>* eg、* input  : ["hello","world","hello world"]* output : [{hello, hello}, {world, world}, {hello world, hello world}]*/
public class MySetCollector2<T> implements Collector<T, Set<T>, Map<T, T>> {@Overridepublic Supplier<Set<T>> supplier() {System.out.println("supplier is invoked!");return TreeSet<T>::new;}@Overridepublic BiConsumer<Set<T>, T> accumulator() {System.out.println("accumulator is invoked!");return (set, item) -> {// 打出当前执行的线程的名称System.out.println("accumulator " + Thread.currentThread().getName());set.add(item);};}@Overridepublic BinaryOperator<Set<T>> combiner() {System.out.println("combiner is invoked!");return (set1, set2) -> {System.out.println("set1: " + set1);System.out.println("set2: " + set2);set1.addAll(set2);return set1;};}@Overridepublic Function<Set<T>, Map<T, T>> finisher() {System.out.println("finisher is invoked!");return set -> {Map<T,T> map = new TreeMap<>();set.forEach(item-> map.put(item,item));return map;};}@Overridepublic Set<Characteristics> characteristics() {System.out.println("supplier is invoked!");return Collections.unmodifiableSet(EnumSet.of(UNORDERED,CONCURRENT));}public static void main(String[] args) {List<String> list = Arrays.asList("hello","world","hello","1","das","v","ads","ads","adsf","adf");for (int i = 0; i < 1; i++) {Set<String> set = new HashSet<>(list);Map<String, String> map = list.parallelStream().collect(new MySetCollector2<>());System.out.println(map);}}
}

  /*** Characteristics indicating properties of a {@code Collector}, which can* be used to optimize reduction implementations.*/enum Characteristics {/*** Indicates that this collector is <em>concurrent</em>, meaning that* the result container can support the accumulator function being* called concurrently with the same result container from multiple* threads.** <p>If a {@code CONCURRENT} collector is not also {@code UNORDERED},* then it should only be evaluated concurrently if applied to an* unordered data source.*/// 指定这个后中间结果只有一个CONCURRENT,/*** Indicates that the collection operation does not commit to preserving* the encounter order of input elements.  (This might be true if the* result container has no intrinsic order, such as a {@link Set}.)*/// 无序的UNORDERED,/*** Indicates that the finisher function is the identity function and* can be elided.  If set, it must be the case that an unchecked cast* from A to R will succeed.*/// 中间结果和返回结果一致时才可以调用IDENTITY_FINISH}

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自定义实现Collector,和对Characteristics的实验

自定义实现Collector,和对Characteristics的实验

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