一:日期與字串轉換
public class DateFormatDemo {

public static void main(String[] args) throws ParseException {	
	//日期轉換成字串
	Date d = new Date();
	SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
	String s = sdf.format(d);
	System.out.println(s);
	
	//字串轉成日期
	String str = "2018-11-20";
	SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd");
	Date dd = sdf2.parse(str);
	System.out.println(dd);			
}
 

}

二:自己封裝一個日期轉換方法(可以把轉換方法dateToString,stringToDate放到一個單獨類中):
public class DateUtilDemo {

public static void main(String[] args) throws ParseException {
	Date d1 = new Date();
	String s1 = dateToString(d1,"yyyy-MM-dd");
	System.out.println(s1);
	
	String s2 = "2018-11-20 12:12";
	Date d2 = stringToDate(s2,"yyyy-MM-dd");
	System.out.println(d2);		
}	
public static String dateToString(Date d,String format) {
	return new SimpleDateFormat(format).format(d);
}
public static Date stringToDate(String s,String format) throws ParseException {
	return new SimpleDateFormat(format).parse(s);
}
 

}