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+# 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/
diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -372,6 +372,23 @@ javac 03-behavioral/mediator/*.java -d out/mediator
 java -cp out/mediator mediator.Main
 ```
 
+### Memento (`03-behavioral/memento/`)
+
+| 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.
+
+Run it:
+```bash
+javac 03-behavioral/memento/*.java -d out/memento
+java -cp out/memento memento.Main
+```
+
 ## Reference
 
 - *Design Patterns: Elements of Reusable Object-Oriented Software* — Gamma, Helm, Johnson, Vlissides