Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Strategy declares an interface common to all supported algorithms. Context uses
this interface to call the algorithm defined by a ConcreteStrategy.
ConcreteStrategy implements the algorithm using the Strategy interface.
Context
is configured with a ConcreteStrategy object.
maintains a reference to a Strategy object.
may define an interface that lets Strategy access its data.