public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Calendar cal = Calendar.getInstance();
        cal.add(Calendar.YEAR, 0);//年
        cal.add(Calendar.MONTH, 0);//月
        cal.add(Calendar.DATE, -1);//日,比当前时间小1天
        cal.add(Calendar.HOUR_OF_DAY, -1);//时,HOUR_OF_DAY是24小时制，HOUR是12小时制
        cal.add(Calendar.MINUTE, 0);//分
        cal.add(Calendar.SECOND, 0);//秒
        Date time = cal.getTime();
        System.out.println(sdf.format(time));
    }

 

public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Calendar cal = Calendar.getInstance();//得到当前时间
        cal.set(2013, 5, 4, 13, 44, 51);//年月日时分秒(月份0代表1月)
        cal.set(Calendar.YEAR, 2014);//年
        cal.set(Calendar.MONTH, 7);//月(月份0代表1月)
        cal.set(Calendar.DATE, 11);//日
        cal.set(Calendar.HOUR_OF_DAY, 15);//时
        cal.set(Calendar.MINUTE, 33);//分
        cal.set(Calendar.SECOND, 32);//秒
        Date time = cal.getTime();
        System.out.println(sdf.format(time));//2014-08-11 15:33:32
    }