I Was not able to save code please some one could help me in resolving the issue



public class PageBlockTableSortingCon {

   private List<Account> accounts;
   private String sortDirection = 'ASC';
   private String sortExp = 'name';

   public String sortExpression
   {
     get
     {
        return sortExp;
     }
     set
     {
       //if the column is clicked on then switch between Ascending and Descending modes
       if (value == sortExp)
         sortDirection = (sortDirection == 'ASC')? 'DESC' : 'ASC';
       else
         sortDirection = 'ASC';
       sortExp = value;
     }
   }

public String getSortDirection()
{
    //if not column is selected
    if (sortExpression == null || sortExpression == '')
      return 'ASC';
    else
     return sortDirection;
}

public void setSortDirection(String value)
{ 
   sortDirection = value;
}
 
   public List<Account> getAccounts() {
       return accounts;
   }


   public PageReference ViewData() {
       //build the full sort expression
       string sortFullExp = sortExpression  + ' ' + sortDirection;
     
       //query the database based on the sort expression
       accounts = Database.query('Select id, Name, BillingCity, BillingCountry, Phone from Account order by ' + sortFullExp + ' limit 1000');
       return null;
   }
}