Java Lambda从入门到精通十九 收集器Collectors API总结

发表于 作者 IT之美
  • Collectors收集器，提供了大量的静态方法对流进行操作
    • 单一求值
      • 求和
        • summingDouble(ToDoubleFunction<? super T> mapper)
        • summingInt(ToIntFunction<? super T> mapper)
        • summingLong(ToLongFunction<? super T> mapper)
      • 求数量
        • counting()
      • 求平均
        • averagingDouble(ToDoubleFunction<? super T> mapper)
        • averagingInt(ToIntFunction<? super T> mapper)
        • averagingLong(ToLongFunction<? super T> mapper)
      • 求最大值
        • maxBy(Comparator<? super T> comparator)
      • 求最小值
        • minBy(Comparator<? super T> comparator)
    • 求值工厂:一次性求和、求数量、求平均、最大、最小值
      • summarizingDouble(ToDoubleFunction<? super T> mapper)
      • summarizingInt(ToIntFunction<? super T> mapper)
      • summarizingLong(ToLongFunction<? super T> mapper)
    • 拼接
      • joining()
    • 分组
      • groupingBy(Function<? super T,? extends K> classifier)
    • 分区
      • partitioningBy(Predicate<? super T> predicate)
    • 规约
      • reducing(BinaryOperator op)
    • 映射
      • toCollection(Supplier collectionFactory)
      • toConcurrentMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper)
      • toList()
      • toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper)
      • toSet()
      • mapping(Function<? super T,? extends U> mapper, Collector<? super U,A,R> downstream)