Loggers are one of most popular examples about interfaces for sure. And there are a lot of implementations of loggers. Some implementations are simple and yet powerful, some implementations may be more complex. All we have to is to select implementation we need and integrate it to our application. It seems like good idea at first place but as soon as we need to switch from one implementation to another we discover nasty dependencies we have to change in all places where we are logging. Let’s see how to avoid these dependencies.