Use the Memento pattern in Java to capture restorable state without exposing internal representation, and know when snapshot cost becomes the real constraint.
The Memento pattern captures object state so it can be restored later without forcing the rest of the system to know the object’s internal structure. In Java, it usually appears in undo stacks, editors, workflow checkpoints, and recovery logic where rollback matters more than continuous recomputation.
The benefit is encapsulation. The cost is snapshot management: memory use, serialization choices, copy depth, and history retention all become part of the design. A Memento implementation that ignores those costs usually starts as a clean abstraction and ends as a hidden storage problem.
Read this section as a state-management section, not just a classic GoF exercise. The child pages cover implementation shape, role boundaries, restoration strategy, serialization trade-offs, and realistic use cases where snapshots beat alternatives such as event logs or explicit version histories.