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Joined 2026-09-21 Message
Incoming links: Strategy pattern
Creational patterns organize object creation; behavioral patterns organize interactions and responsibility for behavior. A creational pattern controls how concrete software objects are selected, instantiated, or shared, so clients need not hard-code the entire construction policy. Examples include the factory method pattern and the singleton pattern.
A behavioral pattern describes how objects collaborate, receive requests, or distribute an algorithm's behavior. For example the observer pattern lets a subject notify dependants after its state changes, and the strategy pattern supplies interchangeable implementations of an operation. This distinction concerns the pattern's principal responsibility; a system can use both kinds together.
The Strategy pattern is a behavioral pattern that encapsulates alternative algorithms behind a shared object interface. A context holds a strategy and delegates the relevant operation to it, letting the chosen algorithm vary independently of its caller.
Use it when the same task has interchangeable policies, such as alternative pricing or route-selection algorithms. Supplying a different strategy changes the policy without expanding a chain of type tests in the context, and each policy can be checked independently. Object composition makes the selected strategy replaceable; clients rely on its contract rather than on one concrete implementation.
The classifications and typical uses are
| Pattern | Category | When to use it |
|---|---|---|
| Command pattern | Behavioral design pattern | Represent a request as an object, separating its invocation from the receiver. Commands can be queued or logged; undo additionally needs enough information to reverse the particular request. |
| Strategy pattern | Behavioral design pattern | Select among interchangeable algorithms through a common interface, such as different routing or scoring policies. |
| Adapter pattern | Structural design pattern | Wrap an existing component so clients can use it through a different required interface without changing that component. |
| State pattern | Behavioral design pattern | Delegate behavior to an object representing the current state, with transitions selecting another state object instead of scattering conditionals across operations. |
| Visitor pattern | Behavioral design pattern | Add operations across a relatively stable element-class hierarchy, commonly through double dispatch. Adding a new element type then usually requires updating the visitors. |