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20230619 java.util.stream.Collectors

发布时间 2023-08-22 17:40:48作者: 流星<。)#)))≦

介绍

  • java.util.stream.Collectors
  • public final class Collectors

API

static

生成集合

  • toCollection
  • toList
  • toUnmodifiableList
  • toSet
  • toUnmodifiableSet

生成 Map

  • toMap
  • toUnmodifiableMap
  • toConcurrentMap

生成字符串

  • joining
    • Collector<CharSequence, ?, String> joining()
    • Collector<CharSequence, ?, String> joining(CharSequence delimiter)
    • Collector<CharSequence, ?, String> joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)

生成 (Int|Long|Double)SummaryStatistics 汇总对象

  • summingInt
  • summingLong
  • summingDouble

平均值

  • averagingInt
  • averagingLong
  • averagingDouble

约简

  • reducing
    • <T> Collector<T, ?, Optional<T>> reducing(BinaryOperator<T> op)
    • <T> Collector<T, ?, T> reducing(T identity, BinaryOperator<T> op)
    • identity 幺元
  • counting
  • minBy
  • maxBy

群组

  • groupingBy
  • groupingByConcurrent
    • 产生 Map ，键是 K ，值是 List<T>

分区

  • partitioningBy
    • 产生 Map ，键是 Boolean ，值是 List<T>

统计

  • summarizingInt
  • summarizingLong
  • summarizingDouble

再处理

  • collectingAndThen
    • <T,A,R,RR> Collector<T,A,RR> collectingAndThen(Collector<T,A,R> downstream, Function<R,RR> finisher)
    • 在收集器后面添加了一个最终处理步骤
  • mapping
    • <T, U, A, R> Collector<T, ?, R> mapping(Function<? super T, ? extends U> mapper, Collector<? super U, A, R> downstream)
    • 反 collectingAndThen
    • 将收集到的元素传给下游处理器
  • filtering
  • flatMapping
  • teeing
    • <T, R1, R2, R> Collector<T, ?, R> teeing(Collector<? super T, ?, R1> downstream1, Collector<? super T, ?, R2> downstream2, BiFunction<? super R1, ? super R2, R> merger)
    • 将两个收集器结果合并为一个