一段简单代码运行的古怪问题，大家帮帮忙啊~~

Question

java.sql.Connection con = java.sql.DriverManager.getConnection(url,user,password);
java.sql.Statement stmt = con.createStatement(java.sql.ResultSet.TYPE_SCROLL_SENSITIVE,java.sql.ResultSet.CONCUR_UPDATABLE);
java.sql.ResultSet rs = stmt.executeQuery("select startDate,endDate,totalDays,type from RT_RecordTime where userId = '20010529162254110' and convert(varchar(7), startDate, 120) = '" + strYear + "-" + strMonth +"'");
System.out.println("******************************************");
List<Calendar> list = new ArrayList<Calendar>();
Calendar cal1 = Calendar.getInstance();
Calendar cal2 = Calendar.getInstance();
while(rs.next())
{
String startDate = rs.getString(1).toString();
System.out.println(startDate+"????????????????");
cal1.set(Integer.parseInt(startDate.substring(0,4)), Integer.parseInt(startDate.substring(5,7))-1, Integer.parseInt(startDate.substring(8,10)));
String d = sdf.format(cal1.getTime());
         System.out.println(d+"KKKKKKKOOOOOOOOOOOOOOOOOOOKKKKKKK");
String endDate = rs.getString(2).toString();
cal2.set(Integer.parseInt(endDate.substring(0,4)), Integer.parseInt(endDate.substring(5,7))-1, Integer.parseInt(endDate.substring(8,10)));
            list.add(cal1);
            while(cal1.compareTo(cal2) != 0)
            {
            
             cal1.add(java.util.Calendar.DATE, 1);
             String s = sdf.format(cal1.getTime());
           //后面这行显示，cal1放进list前还是各不相同的~~
             System.out.println(s+"VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVv");
             list.add(cal1);
            }
}
        //晕死，后面这三行输出的结果居然相同，~~
System.out.println(sdf.format(list.get(0).getTime()));
System.out.println(sdf.format(list.get(1).getTime()));
System.out.println(sdf.format(list.get(2).getTime()));

Answer 1

Calendar.getInstance() 是获取日历的实例， cal1 和 cal2是指向同一个对象的，和list中的对象一样,list[0] list[1] list[2]也是指向同一个对象d的，就是Calendar的唯一实例. 

Answer 2

感谢楼上的回复，不过还是不太明白，你的意思是因为我存进去的都是cal1对象，所以list里面的值都是一样？？？？？？？？

Answer 3

cal1  cal2 list[0]   list[1]   list[2] 是不同的指针（变量），而他们都是指向同一个对象
Calendar   cal1   =   Calendar.getInstance(); 
Calendar   cal2   =   Calendar.getInstance();
这两句就相当于
Calendar   cal1   =   Calendar.getInstance(); 
Calendar   cal2   =   cal1;