Calling a apex class method inside another class

Class 1:
public class IPgap 
{
   public Opportunity  opp{get; set;}
   public IPgap (ApexPages.StandardController controller)
      {
         //Some logic
      }
   private void Info(){
        intrest = new List<SelectOption>();
     }
}

Class 2:

global without sharing class ipHelper {
    //variable declarations
 public void method1() 
    {
         Opportunity opp = new Opportunity();
         ApexPages.StandardController sc = new ApexPages.StandardController(opp);

        IPgap ipreq = new IPgap(sc);
        string returnValue = ipreq.Info();
    }
}