You're building a collection that stores data in a custom tree structure. You want to iterate over all elements, but exposing the internal structure would break encapsulation. The Iterator pattern…
You're building a text editor with undo/redo functionality. Every action (typing, deleting, formatting) needs to be reversible. How do you track what happened and how to undo it? The Command…
You're building an expense approval system. Expenses under £100 can be approved by a manager, under £1000 by a director, and above that by a VP. Hardcoding these rules creates…