How to get User Details in sharepoint.

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1. 
   Dim user As SPUser = SPContext.Current.Web.CurrentUser
   
2. 
   Checking is current login is admin or not?
   
   SPContext.Current.Web.CurrentUser.IsSiteAdmin
   
3. 
   This will give, all group, which are present in current site
   
   SPContext.Current.Web.Groups
   
   This will give the group name of current user
   
   SPContext.Current.Web.CurrentUser.Groups
   
4. 
   Here i m getting all user and add in one DropDownList
   
   Dim websp As SPWeb = SPContext.Current.Site.RootWeb
   Dim users As SPUserCollection = websp.AllUsers
   For Each i As SPUser In users
   dropdownlist1.Items.Add(CStr(i.Name))