Calling privated methods of a standar class from other zclass

Hi all.

I trying to call a privated method of a STANDAR_YYYY standar class(this class have all its methods privated). I see that this Class have a interface IF_STANDARD_YYY.

I have other ZXXXX class and it have one attribute YYYY_ATTR TYPE REF TO STANDAR_YYYY. In a method i instance the standar class (create object YYYY_ATTR...) but when i try to call a method <b>YYYY_ATTR->method1</b> i have a error activing the object ("you cannot access privated method YYYY_ATTR->method1). I was thinking that maybe using the interface IF_STANDAR_YYY in my ZXXXX class i will to call the private methods of the standar class STANDAR_YYY but when i did it obtanin this error "Before the IF_STANDARD_YYY statment, the interface in question must be fully defined". <b>What is wrong ?????</b>. If anybody can help me please!!!