【有趣的实验】JAVA 遍历数组的几种方式的耗时对比

一、前言

出于对遍历方式的耗时想法，是普通for循环、fori、foreach、迭代器 iterator、还是steam流的形式哪种耗时更少呢？

首先添加一个List 集合，这边采用ArraryList

        ArrayList<Integer> list = new ArrayList<Integer>();
        list = new ArrayList<Integer>();
        long startTime = System.currentTimeMillis();
        for (int i = 0; i < 10000000; i++) {
            list.add(i);
        }

下面是几种方式

1.1、普通for循环

    long startTime = System.currentTimeMillis();
    for (int i = 0; i < list.size(); i++) {
        int a = 0;
        a += list.get(i);
    }
    System.out.println("耗时：" + (System.currentTimeMillis() - startTime));

1.2 增强for循环

    long startTime = System.currentTimeMillis();
    for (Integer itr : list) {
        int a = 0;
        a += itr;
    }
    System.out.println("增强for耗时：" + (System.currentTimeMillis() - startTime));

 1.3 迭代器

        long startTime3 = System.currentTimeMillis();
        Iterator<Integer> iterator = list.iterator();
        while (iterator.hasNext()) {
            int xx=0;
            Integer next = iterator.next();
            xx += next;
        }
        System.out.println("迭代器耗时：" + (System.currentTimeMillis() - startTime3));

1.4 forEach

       long startTime4 = System.currentTimeMillis();
        list.forEach(integer -> {
            int xx=0;
            xx += integer;
        });
        System.out.println("foreach耗时：" + (System.currentTimeMillis() - startTime4));

1.5 stream流

        long startTime5 = System.currentTimeMillis();
        list.stream().forEach(integer -> {
            int xx=0;
            xx += integer;
        });
        System.out.println("stream流耗时：" + (System.currentTimeMillis() - startTime5));

一千万数据在耗时情况如下：

 可以看到普通for循环时间更少。