java 日历类Calendar用法

Date as = new Date(new Date().getTime()-24*60*60*1000);
  SimpleDateFormat matter1 = new SimpleDateFormat("yyyy-MM-dd");
  String time = matter1.format(as);
  System.out.println(time);

Calendar calendar = new GregorianCalendar();
 calendar.setTime(date);
 calendar.add(calendar.DATE,1);//把日期往后增加一天.整数往后推,负数往前移动
 date=calendar.getTime(); //这个时间就是日期往后推一天的结果 

/** 
* 获得指定日期的前一天 
* @param specifiedDay 
* @return 
* @throws Exception 
*/ 
public static String getSpecifiedDayBefore(String specifiedDay){ 
//SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd"); 
Calendar c = Calendar.getInstance(); 
Date date=null; 
try { 
date = new SimpleDateFormat("yy-MM-dd").parse(specifiedDay); 
} catch (ParseException e) { 
e.printStackTrace(); 
} 
c.setTime(date); 
int day=c.get(Calendar.DATE); 
c.set(Calendar.DATE,day-1); 

String dayBefore=new SimpleDateFormat("yyyy-MM-dd").format(c.getTime()); 
return dayBefore; 
} 
/** 
* 获得指定日期的后一天 
* @param specifiedDay 
* @return 
*/ 
public static String getSpecifiedDayAfter(String specifiedDay){ 
Calendar c = Calendar.getInstance(); 
Date date=null; 
try { 
date = new SimpleDateFormat("yy-MM-dd").parse(specifiedDay); 
} catch (ParseException e) { 
e.printStackTrace(); 
} 
c.setTime(date); 
int day=c.get(Calendar.DATE); 
c.set(Calendar.DATE,day+1); 

String dayAfter=new SimpleDateFormat("yyyy-MM-dd").format(c.getTime()); 
return dayAfter; 
}