32 lines
1.4 KiB
Markdown
32 lines
1.4 KiB
Markdown
# Memento Design Pattern — Java Example
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**Pattern:** Behavioral → Memento
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**Article:** https://ankurm.com/memento-design-pattern-java/
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## What this example shows
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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.
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## How to run
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```bash
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javac memento/*.java -d out/memento
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java -cp out/memento memento.Main
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```
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Requires Java 25.
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## Post Section ↔ File Mapping
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| Post Section | File(s) |
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|---|---|
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| The Memento: Immutable and Opaque | `EditorMemento.java` |
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| The Originator (Editor) | `Editor.java` |
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| The Caretaker (History) | `History.java` |
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| Wiring it together (Main demo) | `Main.java` |
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Note: the "Serialization as Memento" snippet (`ObjectOutputStream`/`ObjectInputStream` example) is illustrative only — it is not part of this repository's runnable example.
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Article: https://ankurm.com/memento-design-pattern-java/
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All patterns: https://ankurm.com/design-patterns-java/
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