Architecture is full of examples of items designed to do more than one thing.  Your smart phone is a flash light.  From my last examples, a chair is also a clothes hanger.  A seat cushion is a flotation device.

Robert Martin said in his book Agile Software Development, Principles, Patterns, and Practice (http://en.wikipedia.org/wiki/Robert_Cecil_Martin),  that every class should have a single responsibility over a part of the function.  The function-part should be encapsulated and the class should do that and only that.