String DateFormat Calendar之间转换

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

public class StringDateFormatCalendar {
    public static void main(String[] args) throws ParseException {
        String dateString  = "2019-6-29";
        DateFormat df = new SimpleDateFormat("yyyy-mm-dd");

        //String to Date
        Date date = df.parse(dateString);
        Calendar calendar = new GregorianCalendar();

        //Date to Calendar
        calendar.setTime(date);
//        System.out.println(calendar);

        System.out.println("日\t一\t二\t三\t四\t五\t六");
        for (int i=0; i<calendar.get(Calendar.DAY_OF_WEEK);i++){
            System.out.print("\t");
        }
        calendar.set(Calendar.DAY_OF_MONTH,1);

        for (int i = 0; i <calendar.getActualMaximum(Calendar.DATE)-1; i++) {
            if (calendar.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY )
                System.out.println("");
            System.out.print(calendar.get(Calendar.DAY_OF_MONTH)+"\t");
            calendar.add(Calendar.DATE,1);
        }

    }
}

后续注意到一个问题：2019年6月其实只有30天，实际打印为31天，测试date为

Tue Jan 29 00:06:00 CST 2019

发现是SimpleDateFormat的格式写错了，不应该是yyyy-mm-dd 应该是yyyy-MM-dd