为什么Java8 Stream什么都没产生？ [英] Why does Java8 Stream generate nothing?

问题描述

import java.util.Comparator;
import java.util.PriorityQueue;


public class TestPQ {
    public static void main(String[] args){
        Comparator<String> comparator = new StringLengthComparator();
        PriorityQueue<String> queue = new PriorityQueue<String>(10, comparator);
        queue.offer("Short");
        queue.offer("ABCahahahha");
        queue.offer("lululu");
        queue.stream().map( s-> {
            System.out.println("queue: "+ s);
            return s;
        });
    }
}

我有这个代码，我希望我会看到短，lululu和ABCahahahha被打印出来。
但是我没有看到它们。我的代码出了什么问题？
编译没问题。我正在使用java 8编译器和运行时。

I have this code and I expect that I would see "Short", "lululu" and "ABCahahahha" been printed out. But I don't see them. what's wrong with my code? Compile is fine. and I am using java 8 compiler and runtime.

推荐答案

map（）方法本身是 middle 并且不强制消耗 Stream 所以将副作用放在那里是一个非常糟糕的主意。

The map() method itself is intermediate and does not enforce the consumption of a Stream so it's a very bad idea to put side effects there.

在这种情况下，您应该使用专用的 forEach（）方法：

In this case, you should use the dedicated forEach() method:

queue.stream()
  .forEach(s -> System.out.println("queue: " + s));

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