Strategy

Category

Behavioral pattern

Problem

Define a family of algorithms, put each one in a separate class, and make them interchangeable at runtime. Useful when you have multiple algorithms for a task and need to switch between them dynamically.

Solution

• Define a Strategy interface with a method for each algorithm
• Create ConcreteStrategy classes, each implementing one algorithm
• The Context holds a reference to a Strategy and delegates to it
• The strategy can be swapped at runtime without changing the Context

Structure

• Strategy: Interface declaring the algorithm method
• ConcreteStrategy: Implements the algorithm
• Context: Uses the Strategy; can accept a new strategy at runtime

Key Benefits

• Swappable algorithms — Switch algorithms at runtime without changing client code
• Eliminates conditionals — No need for switch/if-else chains selecting algorithms
• Open/Closed Principle — New strategies can be added without modifying the Context

Trade-offs

• Client must understand differences — Client needs to know which strategy to choose
• More objects — Each algorithm becomes a separate class

When to Use

• Many related classes differ only in their behavior
• You need to switch algorithms at runtime
• You want to hide algorithm complexity from clients
• Algorithms are related but have different implementations

Examples

• Java
• Payment processing (credit card, PayPal, Stripe as interchangeable strategies)
• Sorting algorithms (quick sort, merge sort, bubble sort as strategies)