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。