#Command

#Overview

Encapsulate a request as an object, allowing parameterization and queuing.

#When to use

• You need undo/redo.
• You want to queue or log operations.

#Java example

interface Command { void execute(); }

class SaveCommand implements Command {
    private final Document doc;
    SaveCommand(Document doc) { this.doc = doc; }
    public void execute() { doc.save(); }
}

class Invoker {
    void run(Command cmd) { cmd.execute(); }
}

#TypeScript example

interface Command { execute(): void; }

class SaveCommand implements Command {
  constructor(private doc: Document) {}
  execute(): void { this.doc.save(); }
}

class Invoker {
  run(cmd: Command): void { cmd.execute(); }
}

#Pros and cons

Pros:

• Supports undo/redo and logging.
• Decouples invoker from receiver.

Cons:

• Many small classes.
• Indirection can be heavy for simple actions.

#Common pitfalls

• Not capturing all necessary state for undo.
• Creating commands for trivial operations.

#Related patterns

• Chain of Responsibility
• Memento