下面是用Java实现今天、昨天、前天的日期小例子,大家可以试试，有什么问题我们互相讨论。

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

public class TestStr {

public static void main(String[] args) {
   getDates();
}

public static void getDates() {
   int currYear,currMonth,currDate;
   Calendar calendar=Calendar.getInstance();
   currYear=calendar.get(Calendar.YEAR);
     currMonth=calendar.get(Calendar.MONTH)+1;
   currDate=calendar.get(Calendar.DATE);
   System.out.println("今天："+currYear+"-"+currMonth+"-"+currDate);
   //判断昨天是不是上一年。
   if (currMonth==1&&currDate==1) {//是一月一号
    System.out.println("--------1111---------");
    System.out.println("昨天是："+(currYear-1)+"-"+12+"-"+31);
    System.out.println("前天是："+(currYear-1)+"-"+12+"-"+(31-1));
   }
   else if (currMonth==1&&currDate==2) {//是一月一号
    System.out.println("--------222---------");
    System.out.println("昨天是："+(currYear)+"-"+currMonth+"-"+(currDate-1));
    System.out.println("前天是："+(currYear-1)+"-"+12+"-"+31);
   }
   else if (currMonth>1&&currDate>2) {
    System.out.println("--------333---------");
    System.out.println("昨天是："+(currYear)+"-"+currMonth+"-"+(currDate-1));
    System.out.println("前天是："+(currYear-1)+"-"+currMonth+"-"+(currDate-2));
   }
   else if (currMonth>1&&currDate==2) {
    System.out.println("--------4444---------");
    System.out.println("昨天是："+(currYear)+"-"+currMonth+"-"+(currDate-1));
    System.out.println("前天是："+(currYear-1)+"-"+(currMonth-1)+"-"+(getLastDayOfUpMonth(currYear,currMonth,currDate)));
   }
   else if (currMonth>1&&currDate==1) {
    System.out.println("--------5555---------");
    System.out.println("昨天是："+(currYear)+"-"+(currMonth-1)+"-"+(getLastDayOfUpMonth(currYear,currMonth,currDate)));
    System.out.println("前天是："+(currYear-1)+"-"+(currMonth-1)+"-"+(getLastDayOfUpMonth(currYear,currMonth,currDate)-1));
   }
  
}

public static int getLastDayOfUpMonth(int year,int month,int date) {
   Calendar calendar = new GregorianCalendar(year,month,date);
   calendar.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
   calendar.add(Calendar.MONTH,-1);//月增减1天
   calendar.add(Calendar.DAY_OF_MONTH,-1);//日期倒数一日,既得到本月最后一天
   //System.out.println("上个月的最后一天是："+calendar.get(Calendar.DATE)+"号");
   return calendar.get(Calendar.DATE);
}

}

 

 

 

 

        Calendar calendar=Calendar.getInstance();
        calendar.add( Calendar.DAY_OF_MONTH, -2 );  减去两天
        SimpleDateFormat dateFm = new SimpleDateFormat("yyyy-MM-dd");   //格式化当前系统日期  
        String dateTime = dateFm.format(calendar.getTime());  获得减去两天后的年月日
        System.out.println(dateTime);