计算质数(极速版)

计算1000000以内的质数只用了398毫秒,闪电一样的速度.

long start = System.currentTimeMillis();

for (int i = 1; i < 100; i++) {
    double r = Math.sqrt(i);
    for (int j = 2; j < r; j++) {
        if(i % j == 0) {
            break;
        }else if( j > r )
        {
            System.out.println(i);
        }
    }
}

long end = System.currentTimeMillis();
System.out.println(end - start);