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