无论我们做什么，流都比 For 循环慢

问题描述

我有一个非常简单的程序

package t;
public class T {

    public static void main(String[] args) {
        for (int i =0; i<10; i++) {
            java.util.List<Character> l = java.util.Arrays.asList('1','2','a','b','3','4','p');
            java.time.Instant then = java.time.Instant.Now();
            java.util.List<Character> numbers1 = l.stream().filter(Character::isDigit).collect(java.util.stream.Collectors.toList());
            long streamTime = java.time.Duration.between(then,java.time.Instant.Now()).toNanos();
            then = java.time.Instant.Now();
            java.util.List<Character> numbers = new java.util.ArrayList<>();
            for (Character c : l) {
                if (Character.isDigit(c)) {
                    numbers.add(c);
                }
            }
            long forLoopTime = java.time.Duration.between(then,java.time.Instant.Now()).toNanos();
            System.out.println(numbers + " For Time taken " + forLoopTime + " Stream Time " + streamTime);
        }
    }
}

在 Java 8 中执行时，以下是 o/p

java t/t

[1,2,3,4] For Time taken 0 Stream Time 54000000
[1,4] For Time taken 0 Stream Time 0
[1,4] For Time taken 1000000 Stream Time 0
[1,4] For Time taken 0 Stream Time 0

同样在 java 16

中执行

java t/T.java

[1,4] For Time taken 37000 Stream Time 701000
[1,4] For Time taken 6000 Stream Time 31000
[1,4] For Time taken 6000 Stream Time 12000
[1,4] For Time taken 5000 Stream Time 11000
[1,4] For Time taken 5000 Stream Time 12000
[1,4] For Time taken 7000 Stream Time 19000
[1,4] For Time taken 6000 Stream Time 18000
[1,4] For Time taken 7000 Stream Time 18000
[1,4] For Time taken 7000 Stream Time 14000
[1,4] For Time taken 6000 Stream Time 20000

在 java 11

中执行时

java t/T.java

[1,4] For Time taken 40000 Stream Time 461000
[1,4] For Time taken 7000 Stream Time 39000
[1,4] For Time taken 5000 Stream Time 17000
[1,4] For Time taken 10000 Stream Time 20000
[1,4] For Time taken 9000 Stream Time 33000
[1,4] For Time taken 8000 Stream Time 22000
[1,4] For Time taken 8000 Stream Time 36000
[1,4] For Time taken 6000 Stream Time 17000
[1,4] For Time taken 6000 Stream Time 14000
[1,4] For Time taken 5000 Stream Time 22000

这表明无论我们使用哪个版本的 JDK，流都比基本的 for 循环慢。我的理解正确吗？我的印象是 JDK 8 可能更慢，但在更高版本的 JDK 中则不然。

解决方法

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