如何计算时间差

编写一个Java程序，通过java.util.Date获取当前的系统时间，使用String类截取时、分、秒部分输出控制台，循环一千万次后，再取得当前的系统时间截取时、分、秒部分输出到控制台。比较时间差？

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package com.suanfa;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class Aoyun {
    public static void main(String[] args) throws Exception {
        GregorianCalendar gc = new GregorianCalendar();
        int nowyear = gc.get(Calendar.YEAR);
        int nowmonth = (gc.get(Calendar.MONTH)) + 1;
        int nowdate = gc.get(Calendar.DATE);
        int nowhour = gc.get(Calendar.HOUR);
        int nowminute = gc.get(Calendar.MINUTE);
        int nowsecond = gc.get(Calendar.SECOND);
        int ap=gc.get(GregorianCalendar.AM_PM);
        String ampm;
        if(ap==0) ampm="上午";
        else ampm="下午";
        System.out.println("现在是北京时间:" + nowyear + "年" + nowmonth + "月"
                + nowdate + "日"+ampm + nowhour + "时" + nowminute + "分" + nowsecond
                + "秒");

        // String strDate1 = "2008-06-2";
        String strDate2 = "2008-08-8";
        String strDate3 = (nowyear + "-" + nowmonth + "-" + nowdate);

        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        // Date d1 = format.parse(strDate1);
        Date d2 = format.parse(strDate2);
        Date d3 = format.parse(strDate3);
        // System.out.println("距离北京奥运会还相差：" + (d2.getTime() - d1.getTime())
        // / 3600000 / 24 + "天");
        System.out.println("距离北京奥运会还相差：" + (d2.getTime() - d3.getTime())
            / 3600000 / 24 + "天");
        
    }
}

自己看吧！