Command

Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

Applicability

• Need to replace callbacks by an object-oriented form
• Need to specify, queue, and execute requests at different times.
• Need to support undo
• Need to support logging chains
• Need to structure a system around high-level operations built on primitive operations

Consequences

• Decouples the object that invokes the operation from the one that knows how to perform it.
• Commands become first-class objects
• Commands can be assembled into composite commands
• Easy to add new commands