Bird
Raised Fist0

You are designing a text editor with undo functionality using the Command pattern. Which design choice best supports undo operations efficiently?

hard📝 Trade-off Q15 of Q15
LLD - Behavioral Design Patterns — Part 1
You are designing a text editor with undo functionality using the Command pattern. Which design choice best supports undo operations efficiently?
AStore a history stack of Command objects and call an <code>undo()</code> method on the last command
BKeep a log of all text changes as strings and replay them to undo
CUse a single Command object that modifies text directly without history
DImplement undo by reloading the entire document from disk
Step-by-Step Solution
Solution:

  1. Step 1: Understand undo with Command pattern

    Each Command object should implement both execute() and undo() methods to reverse its action.

  2. Step 2: Evaluate design choices

    Storing a history stack of Command objects allows calling undo() on the last command efficiently. Other options either lack command encapsulation or are inefficient.

  3. Final Answer:

    Store a history stack of Command objects and call an undo() method on the last command -> Option A

  4. Quick Check:

    Undo = command history stack with undo() [OK]
Quick Trick: Undo needs command history with undo method [OK]
Common Mistakes:
MISTAKES
  • Using string logs instead of command objects
  • Not implementing undo in commands
  • Reloading entire document is inefficient

Want More Practice?

15+ quiz questions · All difficulty levels · Free

Free Signup - Practice All Questions
More LLD Quizzes
Behavioral Design Patterns — Part 1 - Template Method pattern - Quiz 15hard Behavioral Design Patterns — Part 1 - State pattern - Quiz 8hard Behavioral Design Patterns — Part 1 - Observer pattern - Quiz 8hard Behavioral Design Patterns — Part 1 - Strategy pattern - Quiz 13medium Design — Elevator System - Elevator, Floor, Request classes - Quiz 8hard Design — Library Management System - Notification system - Quiz 2easy Design — Library Management System - Reservation and hold system - Quiz 6medium Design — Library Management System - Why library management tests CRUD design - Quiz 5medium Design — Tic-Tac-Toe Game - Win condition checking - Quiz 2easy Design — Tic-Tac-Toe Game - Requirements and game rules - Quiz 1easy