Command pattern for undo in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the Command Pattern for Undo

Which of the following best describes the role of the Command object in implementing undo functionality?

A It directly modifies the user interface without storing any state.

B It stores the action and its inverse operation to allow undoing the action later.

C It only logs the action name without any data to revert changes.

D It executes the action but does not support undo operations.

💡 Hint

Think about how undo requires reversing an action.

The Command object encapsulates both the action and the logic to undo it, enabling the system to revert changes when needed.

❓ Architecture

intermediate

Designing Undo with Command Pattern Components

In a system using the Command pattern for undo, which component is responsible for keeping track of executed commands to support undo operations?

A Command objects themselves keep a global list of all commands.

B Receiver stores the history of commands executed.

C Client directly calls undo methods on commands without tracking.

D Invoker maintains a stack of executed Command objects.

💡 Hint

Consider which part initiates commands and can manage their order.

The Invoker executes commands and keeps a stack of them to allow undoing in reverse order.

❓ scaling

advanced

Scaling Undo in a Multi-User Collaborative System

When scaling undo functionality using the Command pattern in a collaborative multi-user environment, which challenge is most critical to address?

A Ensuring command history consistency across users to avoid conflicts during undo.

B Ignoring command dependencies and undoing commands in any order.

C Allowing each user to undo only their last command without coordination.

D Storing commands only on the client side without synchronization.

💡 Hint

Think about how multiple users' actions affect shared state.

In collaborative systems, command histories must be consistent and coordinated to prevent conflicts when undoing actions.

❓ tradeoff

advanced

Tradeoffs in Storing Command State for Undo

What is a key tradeoff when deciding how much state to store inside Command objects to support undo?

A More stored state increases memory use but simplifies undo logic.

B Less stored state reduces memory but makes undo impossible.

C Storing no state always improves performance without drawbacks.

D Storing state externally always eliminates the need for Command objects.

💡 Hint

Consider memory use versus ease of undo implementation.

Storing more state inside commands uses more memory but makes undo easier and more reliable.

❓ component

expert

Request Flow in Command Pattern Undo Implementation

Given a system using the Command pattern with undo, what is the correct sequence of steps when a user performs an action and then undoes it?

A 1,2,4,3,5,6,7

B 1,3,2,4,5,6,7

C 1,2,3,4,5,6,7

D 1,2,3,5,4,6,7

💡 Hint

Follow the logical flow of action execution and undo.

The user triggers an action, the Invoker creates and executes the Command, which calls the Receiver. The Command is pushed to the undo stack. On undo, the Invoker pops the Command and calls its undo method on the Receiver.