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聚合操作一定会使流关闭吗？

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用户5273497715

#1 Created at ... [Delete] [Delete and Lock User] 
Stream<Integer> sum = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9);
sum.reduce(0, (acc, n) -> acc + n);
sum.forEach(System.out::println); //就是他导致了程序抛出异常

Exception in thread "main" java.lang.IllegalStateException: stream has already been operated upon or closed
        at java.base/java.util.stream.AbstractPipeline.sourceStageSpliterator(AbstractPipeline.java:279)
        at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:658)
        at com.learnjava.App.main(App.java:15)

如果我要对流进行后续的操作，比如这需要遍历输出，应该怎么做？

廖雪峰

#2 Created at ... [Delete] [Delete and Lock User]

流的特点是每个元素只遍历一次，聚合操作无非就是一个遍历+累加计算的过程，内部已经自动帮你遍历了

你想再遍历一遍，那只能构造一个新的stream

本当問題無

#3 Created at ... [Delete] [Delete and Lock User]

如果需要输出每次累加的结果，应将输出写在 reduce 的方法体里

Stream<Integer> sum1 = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9);
sum1.reduce(0, (acc, n) -> {
  System.out.println(acc = acc + n);
  return acc;
});

服饰店钨丝

#4 Created at ... [Delete] [Delete and Lock User]

Mathematica 的 foldlist

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