hocam fark var tabi, cross platform çalışmadığı için arkadaşın haberi yok muhtemelen. Mesela c# ile bir servis geliştirip parametre olarak Double almak ile double almak arasında fark var. Mesela java da double primitive tip ama Double bir objecttir.
verdiğim linklerin açıklamaları için şu alıntıları kullanarak anlayabilirsin
Alıntı
double is not an alias for Double, it is an alias for System.Double. Which means that there is a very important difference between double and Double: double will always refer to System.Double, Double will refer to whichever Double happens to be in scope.
Alıntı
There is a very important difference between double and Double: double will always refer to System.Double, Double will refer to whichever Double happens to be in scope. Also, I believe that double is not part of ECMA C# or ISO C#, only Microsoft Visual C#, so it is not guaranteed to work cross-platform.