asmhatreandClaude Sonnet 5.5
c8588ae520
Co-Authored-By: Claude Sonnet 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_017ic4b4BL3cEPHQTk2McE7C
49 lines
3.3 KiB
Markdown
49 lines
3.3 KiB
Markdown
# copying
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Companion code for the ankurm.com post *"Deep Copy vs Shallow Copy in Java: clone(), Copy Constructors, Serialization and Records."*
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Module in `java-core-examples`, the Java-core series. There is no `docs/` folder: the deeper material lives in the post itself, inside its expandable sections.
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## Versions this was built and tested against
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| Component | Version | Notes |
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| JDK | 25.0.5+8 (Temurin, LTS) | Records, `List.copyOf`, `Arrays.copyOf`. |
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| JUnit Jupiter | 5.11.0 | Same as the sibling modules. |
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| Maven | 3.9.11 | |
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## Quickstart
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```bash
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export JAVA_HOME=/path/to/jdk-25
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mvn compile
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scripts/run.sh CloneDemo # one demo
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scripts/broken.sh # the three deliberate compile errors
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scripts/run-all.sh # regenerate every file in output/
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```
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## What's in here
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| File | What it shows |
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|---|---|
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| `ShallowVsDeepDemo.java` | Assignment vs shallow copy vs deep copy on one `Person` graph. |
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| `CloneDemo.java` | `clone()` skips the constructor, is shallow, needs `Cloneable`, and a parent that uses `new` breaks subclasses. Arrays and `ArrayList.clone()` are shallow too. |
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| `src/broken/FinalFieldClone.java` | Does not compile: a `final` field cannot be deep-copied inside `clone()`. Not part of the Maven build. |
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| `src/broken/ForgotToOverride.java` | Does not compile: `implements Cloneable` without a public `clone()` override leaves `clone()` protected. |
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| `src/broken/WithExpression.java` | Does not compile on JDK 25: the `with` expression of JEP 468 (derived record creation) is not part of the language yet. |
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| `CopyConstructorDemo.java` | Copy constructors with `final` fields, subtype slicing, and a virtual `copy()` that fixes it. |
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| `SerializationCopyDemo.java` | Deep copy via `ObjectOutputStream`: `transient` loss, shared references and cycles preserved, `NotSerializableException`. |
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| `RecordCopyDemo.java` | Records are only shallowly immutable: `List.copyOf` in the compact constructor, withers, a mutable `Date` component. |
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| `DefensiveCopyDemo.java` | Leaks through constructor and getter; `unmodifiableList` (view) vs `List.copyOf` (snapshot). |
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| `CollectionCopyDemo.java` | Every standard list, map and array copy is shallow; the deep versions. |
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| `CopyOfIdentityDemo.java` | When `List.copyOf` returns the same instance and when it copies; null elements. |
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| `GraphCopyDemo.java` | Shared nodes and cycles: a recursive copy constructor duplicates the shared node and overflows the stack on a cycle; an identity-map copy and serialization both handle them. |
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| `SerializationRulesDemo.java` | Which constructors run during a serialization copy (classes vs records) and an `ObjectInputFilter` allow-list. |
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| `RecordArrayDemo.java` | An array record component leaks through the constructor and the accessor; the generated `equals()` compares arrays by identity. |
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| `DefensiveCloneDemo.java` | Why a defensive copy must not call `clone()` on a non-final parameter type (a `Date` subclass hands back itself). |
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| `CopyCostDemo.java` | Indicative cost of copy constructor vs `clone()` vs serialization. Timing: results drift per run. |
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| `CopyingTest.java`, `CopyingExtrasTest.java` | Pin every claim above as an assertion (17 + 7 = 24 tests). |
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| `output/01-17` | Captured runs of everything above. `10-cost.txt` is the only non-deterministic file. |
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## License
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MIT - see [LICENSE](../LICENSE).
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