【java】Java像数据库一样加减操作时间

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

public class test {
    public static void main(String[] args) throws ParseException {
        DateFormat d = new SimpleDateFormat("yyyy-MM-dd");
        System.out.println(d.format(new Date()));
        Calendar c = Calendar.getInstance();
        c.setTime(d.parse(d.format(new Date())));
        c.set(Calendar.DATE, c.get(Calendar.DATE)-9);
        String t = d.format(c.getTime());
        System.out.println(t);
    }
}import java.text.DateFormat;
import java.