I knew the Command pattern going in but I still fumbled the undo stack explanation at first.
Start by defining a Command interface with execute and undo methods, then implement a basic invoker that maintains a history stack for undo. For extensions, discuss adding a redo stack, a composite command for grouping, and a marker interface or exception for non-undoable commands, emphasizing trade-offs like memory vs. functionality.
Pro tip: At Netflix, reliability and scalability matter: mention that you'd consider memory management for history stacks (e.g., limiting size or using persistent storage) and idempotency for non-undoable commands to avoid inconsistent states.
Ask about expected command types, undo/redo depth, concurrency needs, and whether commands can be non-undoable. This shows you think about real-world usage before designing.
Define a Command interface with execute() and undo() methods. Implement a simple invoker that stores executed commands in a stack for undo.
Add a redo stack: when undoing, push the command onto the redo stack; when redoing, pop from redo and execute. Clear redo stack on new command execution.
Introduce a CompositeCommand that holds a list of commands and executes/undoes them in sequence. Ensure atomicity by rolling back on failure if needed.
Use a marker interface (e.g., NonUndoableCommand) or throw an exception on undo. Discuss strategies like logging, compensating actions, or preventing undo for such commands.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.