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asmhatreandClaude Sonnet 5.5 c8588ae520 copying: fold in graph copying (shared nodes, cycles, identity-map fix), serialization rules (constructors, record canonical constructor, ObjectInputFilter), record array components, clone() as a defensive copy, two more compile-error exhibits; 24 tests

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b4BL3cEPHQTk2McE7C

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output

copying: fold in graph copying (shared nodes, cycles, identity-map fix), serialization rules (constructors, record canonical constructor, ObjectInputFilter), record array components, clone() as a defensive copy, two more compile-error exhibits; 24 tests

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scripts

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src

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pom.xml

copying: deep vs shallow copy module (clone() traps, copy constructors, serialization copy, records, defensive copies, collection copies), 17 contract tests

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README.md

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README.md

copying

Companion code for the ankurm.com post "Deep Copy vs Shallow Copy in Java: clone(), Copy Constructors, Serialization and Records." 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.

Versions this was built and tested against

Component	Version	Notes
JDK	25.0.5+8 (Temurin, LTS)	Records, `List.copyOf`, `Arrays.copyOf`.
JUnit Jupiter	5.11.0	Same as the sibling modules.
Maven	3.9.11

Quickstart

export JAVA_HOME=/path/to/jdk-25
mvn compile
scripts/run.sh CloneDemo          # one demo
scripts/broken.sh                 # the three deliberate compile errors
scripts/run-all.sh                # regenerate every file in output/

What's in here

File	What it shows
`ShallowVsDeepDemo.java`	Assignment vs shallow copy vs deep copy on one `Person` graph.
`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.
`src/broken/FinalFieldClone.java`	Does not compile: a `final` field cannot be deep-copied inside `clone()`. Not part of the Maven build.
`src/broken/ForgotToOverride.java`	Does not compile: `implements Cloneable` without a public `clone()` override leaves `clone()` protected.
`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.
`CopyConstructorDemo.java`	Copy constructors with `final` fields, subtype slicing, and a virtual `copy()` that fixes it.
`SerializationCopyDemo.java`	Deep copy via `ObjectOutputStream`: `transient` loss, shared references and cycles preserved, `NotSerializableException`.
`RecordCopyDemo.java`	Records are only shallowly immutable: `List.copyOf` in the compact constructor, withers, a mutable `Date` component.
`DefensiveCopyDemo.java`	Leaks through constructor and getter; `unmodifiableList` (view) vs `List.copyOf` (snapshot).
`CollectionCopyDemo.java`	Every standard list, map and array copy is shallow; the deep versions.
`CopyOfIdentityDemo.java`	When `List.copyOf` returns the same instance and when it copies; null elements.
`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.
`SerializationRulesDemo.java`	Which constructors run during a serialization copy (classes vs records) and an `ObjectInputFilter` allow-list.
`RecordArrayDemo.java`	An array record component leaks through the constructor and the accessor; the generated `equals()` compares arrays by identity.
`DefensiveCloneDemo.java`	Why a defensive copy must not call `clone()` on a non-final parameter type (a `Date` subclass hands back itself).
`CopyCostDemo.java`	Indicative cost of copy constructor vs `clone()` vs serialization. Timing: results drift per run.
`CopyingTest.java`, `CopyingExtrasTest.java`	Pin every claim above as an assertion (17 + 7 = 24 tests).
`output/01-17`	Captured runs of everything above. `10-cost.txt` is the only non-deterministic file.

License

MIT - see LICENSE.