Calendar获取星期

Calendar的使用举个小栗子：

//通过当前时间获取本周周一时间

Date date = new Date();
Calendar calendar = new GregorianCalendar(); 
calendar.setTime(date ); 
calendar.add(Calendar.DATE,i + 1 - (calendar.get(Calendar.DAY_OF_WEEK) - 1) );
date = calendar.getTime();