Command pattern in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the Command pattern?

The Command pattern encapsulates a request as an object, allowing you to parameterize clients with queues, requests, and operations. It separates the object that invokes the operation from the one that knows how to perform it.

beginner

Name the four main components of the Command pattern.

1. Command: declares an interface for executing an operation.<br>2. ConcreteCommand: implements the Command interface and defines the binding between a Receiver and an action.<br>3. Receiver: knows how to perform the operations.<br>4. Invoker: asks the command to carry out the request.

intermediate

How does the Command pattern help in implementing undo functionality?

By storing command objects that represent actions, the system can reverse or undo actions by calling an undo method on the stored commands, since each command knows how to undo its own operation.

intermediate

Explain how the Command pattern supports queuing and logging of requests.

Since commands are objects, they can be stored in queues or logs. This allows requests to be executed later, retried, or audited by replaying the stored commands.

beginner

What real-life example can help understand the Command pattern?

Think of a remote control (Invoker) that sends commands to devices like a TV or stereo (Receivers). Each button press is a command object that tells the device what to do, separating the button from the device's internal workings.

Which component in the Command pattern knows how to perform the actual work?

A Invoker

B Receiver

C ConcreteCommand

D Client

The Receiver is the component that knows how to perform the actual operations requested by the command.

What is the role of the Invoker in the Command pattern?

A Defines the command interface

B Performs the actual operation

C Executes the command

D Stores and calls commands

The Invoker stores commands and triggers their execution but does not know the details of the operation.

How does the Command pattern help with undo operations?

A By logging errors

B By storing the state of the system

C By encapsulating requests as objects with undo methods

D By using callbacks

Commands can implement undo methods to reverse their actions, enabling undo functionality.

Which of these is NOT a benefit of the Command pattern?

A Automatically optimizes performance

B Supports queuing requests

C Decouples sender and receiver

D Enables logging and undo

The Command pattern does not automatically optimize performance; it focuses on decoupling and flexibility.

In the Command pattern, what does the ConcreteCommand do?

A Implements the command and binds it to a receiver

B Stores commands in a queue

C Invokes the command

D Defines the interface for commands

ConcreteCommand implements the command interface and binds the command to a specific receiver.

Describe the Command pattern and explain its main components and their roles.

Think about how requests are turned into objects and who does what.

Explain how the Command pattern can be used to implement undo functionality and request queuing.

Focus on how commands can be saved and reversed.