> For AI agents: the complete documentation index is available at https://nhanbe.id.vn/llms.txt, the full documentation bundle is available at https://nhanbe.id.vn/llms-full.txt.

# 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

```java
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

```ts
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](https://nhanbe.id.vn/design-patterns/behavioral/chain-of-responsibility.md)
- [Memento](https://nhanbe.id.vn/design-patterns/behavioral/memento.md)