Java8流的顺序执行和并行执行产生不同的结果？

从reduce的文档中：

身份值必须是累加器功能的身份。这意味着对于所有t，accumulator.apply（identity，t）等于t。

在您的情况下，这是不正确的-“”和“ a”创建了“ / a”。

我已经提取了累加器功能并添加了打印输出以显示发生了什么：

BinaryOperator<String> accumulator = (s1, s2) -> {    System.out.println("joining "" + s1 + "" and "" + s2 + """);    return s1 + "/" + s2;};System.out.println(Stream     .of("a", "b", "c", "d", "e", "f")     .parallel()     .reduce("", accumulator));

这是示例输出（运行之间有所不同）：

joining "" and "d"joining "" and "f"joining "" and "b"joining "" and "a"joining "" and "c"joining "" and "e"joining "/b" and "/c"joining "/e" and "/f"joining "/a" and "/b//c"joining "/d" and "/e//f"joining "/a//b//c" and "/d//e//f"/a//b//c//d//e//f

您可以在函数中添加if语句以分别处理空字符串：

System.out.println(Stream        .of("a", "b", "c", "d", "e", "f")        .parallel()        .reduce((s1, s2) -> s1.isEmpty()? s2 : s1 + "/" + s2));

正如Marko Topolnik所注意到的，

s2