并行流

从集合中获取并行流：Stream paralleWords = words.parallelStream();

parallel方法将任意顺序流转换为并行流：Stream paralleWords = Stream.of(wordArray).parallel();

以下是不好的示范，假设对字符串的所有短单词计数：

package streams;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Arrays;
import java.util.List;

public class BadParalleWords {
    
    public static void main(String[] args) throws IOException {
        Path path = Path.of("./resources/alice.txt");
        var contents = Files.readString(path);
        List<String> words = List.of(contents.split("\\PL+"));
        var shortWords = new int[12];
        words.parallelStream().forEach(
            s -> {if(s.length()<12) shortWords[s.length()]++;}
        );
        System.out.println(Arrays.toString(shortWords));
    }

}

结果是多次数据不准确，经典的竞争情况。