需求

用Java把字串表示的日期按要求自動變為多少天前，多少天后？

程式碼

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

public class Hello {
    // @author 孫琨
    public static void main(String[] args) {
        // TODO Auto-generated method stub
 

//      Date d = new Date();
//      SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
//      String dateNowStr = sdf.format(d);
//      System.out.println("格式化後的日期:" + dateNowStr);
//      boolean s1 = true;
//      boolean s2 = true;
//      boolean s = false;
//      s = s1 && s2;
//      System.out.println(s);
 


        String logDay = "20170501";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
        try {
            Date date = sdf.parse(logDay);
            Calendar calendar = new GregorianCalendar();
            calendar.setTime(date);
            calendar.add(calendar.DATE, -1); // 負數為提前幾天，正數為推遲幾天
 

            date = calendar.getTime();
            String greenDay = sdf.format(date);
            System.out.println(greenDay);
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}