# Memento Design Pattern — Java Example

**Pattern:** Behavioral → Memento
**Article:** https://ankurm.com/memento-design-pattern-java/

## What this example shows

A text editor with undo support that doesn't leak its internal state. `EditorMemento` is an immutable snapshot with package-private accessors — only `Editor` (in the same package) can read it back; everyone else can only call `toString()`. `Editor` is the originator: it packs its fields into a memento on `save()` and unpacks them on `restore()`. `History` is the caretaker: it pushes and pops mementos on a stack without ever inspecting their contents. `Main` types text, saves checkpoints after most edits (deliberately skipping one, to show it's lost on undo), then undoes twice.

## How to run

```bash
javac memento/*.java -d out/memento
java -cp out/memento memento.Main
```

Requires Java 25.

## Post Section ↔ File Mapping

| Post Section | File(s) |
|---|---|
| The Memento: Immutable and Opaque | `EditorMemento.java` |
| The Originator (Editor) | `Editor.java` |
| The Caretaker (History) | `History.java` |
| Wiring it together (Main demo) | `Main.java` |

Note: the "Serialization as Memento" snippet (`ObjectOutputStream`/`ObjectInputStream` example) is illustrative only — it is not part of this repository's runnable example.

Article: https://ankurm.com/memento-design-pattern-java/
All patterns: https://ankurm.com/design-patterns-java/