Behavioural Design Pattern: Strategy Design pattern

Define Strategy Design pattern

This design defines a set of algorithms, encapsulates each one, and makes them interchangeable. It enables a client to select an algorithm from a family of algorithms at runtime and provides a simple interface to access it.

Examples of Strategy Patterns

Examples of strategy patterns include:

• Discount Strategy
• Payment Strategy

Strategy Pattern with UML diagram

The classes, interfaces, & objects in the above UML class diagram are defined as follows:

• Context: This is a class with a property that stores the reference to a Strategy object. This property will be set at runtime based on the necessary algorithm.
• Strategy: This interface allows the Context object to call the algorithm provided by a ConcreteStrategy.
• ConcreteStrategyA/B: These classes implement the Strategy interface.

When Should the Strategy Design Pattern Be Used?

The Strategy design pattern is applicable in the following scenarios:

• There are several strategies for a given problem, and the selection criteria for each strategy are established at runtime.
• Many related classes just differ in their behavior.
• The strategies rely on data to which the client has no access.

Advantages of the Strategy Design Pattern

• Flexibility: The ability to flexibly change the behavior of an object.
• Loose Coupling: The strategy classes are independent of one other and the context class, allowing for loose coupling.
• Reuse: Strategies can be applied in a variety of settings.
• Isolation: Each approach may be implemented and maintained independently of the others.
• Open/Closed Principle: New strategies can be implemented without altering the context.