A Caller represents the class calling the method which generates this Caller. It retrieves information from the stack trace and is a relatively expensive operation. As a result, it should be used only when there is an absolute need.
Author: Hugo Y. K. Lam
Gets the line number in the source file of the caller class at which the call is made.
Returns: the line number in the source file.
Checks if the calling class is undetermined.
Returns: true if the calling class is undetermined.