Policy

Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

Use the Strategy pattern when

• many related classes differ only in their behavior. Strategies provide a way to configure a class either one of many behaviors
• you need different variants of an algorithm. for example, you might define algorithms reflecting different space/time trade-offs. Strategies can be used when these variants are implemented as a class hierarchy of algorithms
• an algorithm uses data that clients shouldn't know about. Use the Strategy pattern to avoid exposing complex, algorithm-specific data structures
• a class defines many behaviors, and these appear as multiple conditional statements in its operations. Instead of many conditionals, move related conditional branches into their own Strategy class

• Design Patterns: Elements of Reusable Object-Oriented Software
• Functional Programming in Java: Harnessing the Power of Java 8 Lambda Expressions