how do I force to call function X?

Hi,
When you have a public class declared and this class is used somewhere outside the class, you want them to invoke the function X before using other functions. What do you do?  
In other words, in a class C, you have a constructor and function X, Y, and Z. When this class is used, you want to make sure function X is the first function called other then the constructor.
 
Is this possible?
Thanks.
...