C#

 var pickLoc = document.getElementById('_pickLoc');//_pickLoc is a Hidden Variable

for (i=1; i<=lastRow; i++) 
    {
        var dataStr;
        var localvar;
       
	  //Validating Container number
      var aRow = document.getElementById('txtRow' + i);
      if (aRow.value.length <= 0) 
      {
        alert('Row ' + i + ': Container number is empty');
        document.getElementById('txtRow' + i).style.backgroundColor = "#ffff99";
        document.getElementById('txtRow' + i).focus();
        return;
       }
       else {
            
            document.getElementById('txtRow' + i).style.backgroundColor = "";
			dataStr = "<tr><td height=5></td></tr><tr><td><FONT face='Verdana' size='1'>";
			dataStr += document.getElementById('txtRow' + i).value;
			dataStr += "</Font></td><td><FONT face='Verdana' size='1'>";
        }
       
       //_cntrSize
      	var e = document.getElementById('_cntrSize' + i);
	  if (e.options[e.selectedIndex].value == "") 
	  {
		 //dataStr +=  '</td></tr><tr>';
		 alert('Row ' + i + ': Container Size is empty');
		 e.style.backgroundColor = "#ffff99";
         e.focus();
         return;
		}
       else {
			 e.style.backgroundColor = "";
			 dataStr += e.options[e.selectedIndex].value;
			 dataStr +=  "</Font></td><td><FONT face='Verdana' size='1'>";
		}
		
		//Pickup Location Type
      var LocRow = document.getElementById('txtLocRow' + i);
      if (LocRow.value.length <= 0) {
        alert('Row ' + i + ': Pick up location is empty');
        document.getElementById('txtLocRow' + i).style.backgroundColor = "#ffff99";
        document.getElementById('txtLocRow' + i).focus();
        return;
       }
       else {document.getElementById('txtLocRow' + i).style.backgroundColor = "";
			 dataStr += document.getElementById('txtLocRow' + i).value;
			 dataStr += "</Font></td><td><FONT face='Verdana' size='1'>";
			 localvar = document.getElementById('txtLocRow' + i).value;
        }
        pickLoc.Value = localvar; 	
	 ttlStr += dataStr;
    }

I have 3 classes overriding a function of base abstract class A. The child classes are 1, 2 & 3. Child classes override function "public abstract void hello(var1, var2)".

Following is what I want to implement:
abstract class A
{
public abstract void hello(var1, var2); // This will be only for class 1 & class 2 (Existing function)
public abstract void hello(var1, var2, var3); // Want to make this available for class 3 only. (Want to add this new function)
}


** Currently the above code throws error and wants me to implement the new inherited abstract function in class 1 & 2.

public abstract class Factory
    {
        private readonly object _instanceLock = new object();
        private Factory _instance = null;

        internal Factory GetInstance(Type t)
        {
            if (_instance != null) return _instance;
            if(t != typeof(Factory)) throw new InvalidOperationException("Factory can't created an instance not derived from " + typeof(Factory).FullName);

            lock (_instanceLock)
            {
                if (_instance != null) return _instance;
                Thread.MemoryBarrier();
                var assembly = Assembly.GetAssembly(t);
                _instance = (Factory)assembly.CreateInstance(t.FullName);
            }

            return _instance;
        }

        protected Factory() { /* Protected -> Singleton */ }
    }