Strategy

The strategy is pattern is like an advanced version of an if else statement. It's basically where you make an interface for a method you have in your base class. This interface is then used to find the right implementation of that method from one of the derived classes. The implementation, in this case, will be decided at runtime based on the client.

This pattern is incredibly useful in situations where you have required and optional methods for a class. Some instances of that class won't need the optional methods and that causes a problem for inheritance solutions. You could use interfaces for the optional methods, but then you would have to write the implementation every time you used that class since there would be no default implementation.

That's where the strategy pattern saves us. Instead of the client looking for an implementation, it delegates to a strategy interface and the strategy finds the right implementation.