Object of an interface inside if-statement in C++

Hello I have a quick question. Since I'm not too familiar with C++ and I'm looking through some Code right now, I wondered what is happening in a function similar to this one:

#include "SomeInterface.h"

class SomeClass {

public:
...

   void SomeFunction(...){

       if (interface) {   //What is asked here exactly?

           /*do something*/

       }

   }

/*...*/
protected:

SomeInterface interface;
}

Since I'm coming from Java I wondered what is asked in the if-brackets. I'm used to only being able to put a lonely variable name in the if-brackets when the variable is of the type bool. But since here it is a custom interface-type I'm confused.

Thank you in advance for your answers.