Java中如何实现时间的加减

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

public class Test {

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

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd");
String str = new SimpleDateFormat("yyyy-mm-dd").format(new Date());
Date dt = sdf.parse(str);
Calendar rightNow = Calendar.getInstance();
rightNow.setTime(dt);
rightNow.add(Calendar.YEAR, -1);// 日期减1年
rightNow.add(Calendar.MONTH, 3);// 日期加3个月
rightNow.add(Calendar.DAY_OF_YEAR, 10);// 日期加10天
Date dt1 = rightNow.getTime();
String reStr = sdf.format(dt1);
System.out.println(reStr);

}

}