nanoTime对volatile 测试的一种写法

今天脑筋有点搭牢，想了半天才看出为什么以下两段代码效果是相同的。。。

第一种好处是可以直接批量复制黏贴system.out,  不用改什么东西

  private static long i;
  private volatile static long vt;
  private static final int TEST_SIZE = 10000000;

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long time = System.nanoTime(); for (int n = 0; n < TEST_SIZE; n++)     vt = System.currentTimeMillis(); System.out.println(-time + (time = System.nanoTime()));<br> for (int n = 0; n < TEST_SIZE; n++)     i = System.currentTimeMillis(); System.out.println(-time + (time = System.nanoTime()));

　　

这种每次要在循环头上重置nanoTime

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private static long i;private volatile static long vt;private static final int TEST_SIZE = 10000000;long time = System.nanoTime(); for (int n = 0; n < TEST_SIZE; n++) {             vt = System.currentTimeMillis(); } System.out.println((System.nanoTime() - time));   time = System.nanoTime(); for (int n = 0; n < TEST_SIZE; n++) {       i = System.currentTimeMillis(); } System.out.println((System.nanoTime() - time));