增强的循环性能比传统的索引查找差吗？

您遇到的问题是，使用迭代器比使用直接查找要慢。在我的机器上，每次迭代的差异约为0.13 ns。相反，使用数组可以为每次迭代节省0.15
ns。在99％的情况下，这应该是微不足道的。

public static void main(String... args) {    int testLength = 100 * 1000 * 1000;    String[] stringArray = new String[testLength];    Arrays.fill(stringArray, "a");    List<String> stringList = new ArrayList<String>(Arrays.asList(stringArray));    {        long start = System.nanoTime();        long total = 0;        for (String str : stringArray) { total += str.length();        }        System.out.printf("The for each Array loop time was %.2f ns total=%d%n", (double) (System.nanoTime() - start) / testLength, total);    }    {        long start = System.nanoTime();        long total = 0;        for (int i = 0, stringListSize = stringList.size(); i < stringListSize; i++) { String str = stringList.get(i); total += str.length();        }        System.out.printf("The for/get List loop time was %.2f ns total=%d%n", (double) (System.nanoTime() - start) / testLength, total);    }    {        long start = System.nanoTime();        long total = 0;        for (String str : stringList) { total += str.length();        }        System.out.printf("The for each List loop time was %.2f ns total=%d%n", (double) (System.nanoTime() - start) / testLength, total);    }}

当运行十亿个条目时，将打印条目（使用Java 6 update26。）

The for each Array loop time was 0.76 ns total=1000000000The for/get List loop time was 0.91 ns total=1000000000The for each List loop time was 1.04 ns total=1000000000

当运行十亿个条目时，将打印条目（使用OpenJDK7。）

The for each Array loop time was 0.76 ns total=1000000000The for/get List loop time was 0.91 ns total=1000000000The for each List loop time was 1.04 ns total=1000000000

即完全一样。;）