3. 系统时间与当前日期的区别？
系统时间确切的说应该是
System.currentTimeMillis();
new Date()是当前日期,虽然它getTime();和System.currentTimeMillis();
一样,但System.currentTimeMillis();
4. 如何计算两个日期的天数差值？
long beginTime = beginDate.getTime();
long endTime2 = endDate.getTime();
long betweenDays = (long)((endTime - beginTime) / (1000 * 60 * 60 *24) + 0.5);
5. 如何比较日期时间大小？
第一种方法：
use Calendar object to compare
java.util.Calendar class can be used to compare date. In order to do this,
you guy should parse that string into int year, month, day and construct a
Calendar object, and then do comparison.
Below is a sample
StringTokenizer token = new StringTokenizer(your string,"-");
int year = Integer.parseInt(token.nextToken());
int month = Integer.parseInt(token.nextToken());
int day = Integer.parseInt(token.nextToken());
Calendar date = Calendar.getInstance();
date.set(year,month,day);
Calendar today = Calendar.getInstacne();
if(date.after(today)){
String newdir=year+month+day;
String wenjian = hh+mm+ss;
7. 怎么得到一个月的天数？
java.util.Calendar date = java.util.Calendar.getInstance();
System.out.println(date.getActualMaximum(date.DAY_OF_MONTH));
