To initialize or set the values of private members in a class from client code, setter methods are commonly used. In Java, this is demonstrated with a class that includes private variables and public getter and setter methods. For C++, the same concept applies. A class can be defined with private member variables, and public methods can be created to modify and access these variables. In the provided C++ example, an instance of the class is created in the main function, and the setter method is used to assign a value to the private member, which can then be retrieved using the getter method. This approach maintains encapsulation while allowing controlled access to private data.