CPU性能测试 java代码

public static void main(String[] args) {
            long startTime = System.currentTimeMillis();
            long endTime = startTime + 6000;
            long index = 0;
            while(true){
                double x = Math.sqrt(index);
                long now = System.currentTimeMillis();
                if (now > endTime) {
                    break;
                }
                index++;
            }
            System.out.println(index+" Loops in 6 seconds");
        }