Java流中的中间操作 [英] Intermediate operation in Java streams

问题描述

在Java 8中，我使用Streams打印输出，但大小即将为0.为什么?

In java 8, I am using Streams to print the output, but size is coming as 0. Why?

public class IntermediateryAndFinal {
    public static void main(String[] args) {
        Stream<String> stream = Stream.of("one", "two", "three", "four", "five");

        Predicate<String> p1 = Predicate.isEqual("two");
        Predicate<String> p2 = Predicate.isEqual("three");

        List<String> list = new ArrayList<>();

        stream.peek(System.out::println)
            .filter(p1.or(p2))
            .peek(list::add);
        System.out.println("Size = "+list.size());
    }
}

推荐答案

理想情况下，您不应更改外部列表，而可以使用 Collectors.toList()将其收集在列表中:

Ideally you should not mutate an external list, instead you can use Collectors.toList() to collect it in a list:

List<String> list = stream.peek(System.out::println)
            .filter(p1.or(p2))
            .collect(Collectors.toList()); // triggers the evaluation of the stream
System.out.println("Size = "+list.size());

在您的示例中，仅当像

allMatch()
anyMatch() 
noneMatch() 
collect() 
count() 
forEach() 
min() 
max() 
reduce()

遇到

.

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