Command Pattern: Making Requests into Objects

interview, best-practices

java java21 scala scala3 kotlin design-patterns command-pattern

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Coming Soon — We're Still Hammering This One Out This post is on the roadmap and is being actively crafted. Think of it as a movie trailer: the good stuff is coming, you just caught us before the popcorn was ready. Check back soon — or bookmark the series guide to track all posts as they land.
⏳  Post in progress

What You'll Learn When This Post Is Ready

• How to encapsulate requests as objects so you can queue, log, and undo them
• How to build a proper undo/redo system — without a tangled mess of flags and special cases
• Why the Command pattern is the secret ingredient in macro recorders, transaction systems, and job queues
• How functional approaches in Scala and Kotlin — using pure functions and immutable state — achieve the same goals more elegantly
• A real-world text editor command example with full undo/redo history
• Side-by-side comparison across Java 21, Scala 3, and Kotlin with full test coverage

Interview Questions You Can Expect

• “How would you implement an undo/redo system? Would you use the Command pattern?”
• “What is the difference between the Command pattern and the Strategy pattern?”
• “How do you manage command history and support undo operations?”
• “Give a real-world example where the Command pattern is genuinely useful.”
• “How do commands compare to functional approaches using first-class functions?”