java 比较时间大小

    String s1="2008-01-25 09:12:09";
        String s2="2008-01-29 09:12:11";
        java.text.DateFormat df=new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        java.util.Calendar c1=java.util.Calendar.getInstance();
        java.util.Calendar c2=java.util.Calendar.getInstance();
        try
        {
            c1.setTime(df.parse(s1));
            c2.setTime(df.parse(s2));
        }catch(java.text.ParseException e){
            System.err.println("格式不正确");
        }
        int result=c1.compareTo(c2);
        if(result==0)
            System.out.println("c1相等c2");
        else if(result<0)
            System.out.println("c1小于c2");
        else
            System.out.println("c1大于c2");

SimpleDateFormat   DateFormat   =   new   SimpleDateFormat("yyyy-MM-dd HH:mm:ss");    
  HH:mm:ss   为24小时 
  hh:mm:ss   为12小时