写一个小程序，用来计算它包含的代码所需的耗时。虽然简单，测试代码是否耗时还是有点用的，不用重新写嘛~

import java.util.Date;

import java.util.concurrent.TimeUnit;

public class TimeLag {

	private Date start;

	private Date end;

	public TimeLag() {

		start = new Date();

	}

	public String cost() {

		end = new Date();

		long c = end.getTime() - start.getTime();

		String s = new StringBuffer().append("cost ").append(c).append(" milliseconds (").append(c / 1000).append(" seconds).").toString();

		return s;

	}

	public static void main(String[] args) throws InterruptedException {

		TimeLag t = new TimeLag();

		TimeUnit.SECONDS.sleep(2);

		System.out.println(t.cost());

	}

}