java计算代码执行时间

public class Demo {
  public static void main(String[] args) throws InterruptedException {
    long start = System.currentTimeMillis();
    long sum = 0;
    for (int i = 0; i <= 100000; i++) {
      sum += i;
    }
    System.out.println("sum = " + sum);
    long end = System.currentTimeMillis(); 
    System.out.println(end - start + "ms");
  }
}