Strategy

The strategy design pattern allows us to set the behavior of a class at runtime. Strategy bases on polymorphism for implementing a series of behaviors that can be interchanged during the execution of the program, allowing for a modification of an object’s behavior by following a strategy that has been set.

The components included in this pattern are:

• Context: This component encapsulates the strategy to be used, which can be set at runtime.
• IStrategy: Common interface all strategies must implement. In it, all the operations the strategies need to implement are defined.
• ConcreteStrategy: It represents the concrete strategies, which inherit from IStrategy.

1. The client creates a new context and sets the StrategyA.
2. The client executes the doSomethingoperation.
3. Context hands over this responsibility to ConcreteStrategyA.
4. ConcreteStrategyA performs the operation and returns the result.
5. Context takes this result and hands it over to the client.
6. The client changes the Context strategy at runtime.
7. The client executes the doSomethingoperation again.
8. Context hands over this responsibility to ConcreteStrategyB.
9. ConcreteStategyB performs the operation and returns the result.
10. Context takes this result and hands it over to the client.

Real-world example

By implementing the Strategy design pattern, we are going to develop an application that offers different authentication methods. User authentication will be achieved via XML file, database or settings file in memory. With the Strategy pattern, the user will be able to establish the preferred authentication method in the application, without having to add any more code.

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