Reference · Defect Inventory

Defect Inventory

Every flaw in the supplied code, with how it was reproduced. Verified against the real starter on 2026-08-30.

How to use this card

This is the master list. Print it, and tick items off as you fix them. Before the interview, read the Severity column and be able to justify the ordering — ranking defects is a more senior skill than finding them.

Tier 1 — must fix (they are the stated requirements)

#	Defect	Evidence	Severity
D1	No tests at all. `src/test/` does not exist.	mvn test → No tests to run.	Graduate requirement unmet
D2	The three exception classes are never used. Nothing imports, throws or catches them.	grep -rn "AlreadyBorrowed Exception" src/main → only its own file	Intermediate requirement unmet
D3	`IOException` signals domain failure. Neither `borrowBook` nor `returnBook` performs I/O.	Signature: `throws IOException`	Wrong abstraction
D4	The library lies. Borrowing an already-borrowed book reports that the book was not found.	IOException: Book not found: Dune (after Dune was added and borrowed)	High — misleads debugging
D5	Same conflation on return. The `"or"` in the message is the smell.	Book not found or not borrowed: Dune	Medium

Defect

Evidence

Severity

No tests at all. src/test/ does not exist.

mvn test →
No tests to run.

Graduate requirement unmet

The three exception classes are never used. Nothing imports, throws or catches them.

grep -rn "AlreadyBorrowed
Exception" src/main → only its own file

Intermediate requirement unmet

IOException signals domain failure. Neither borrowBook nor returnBook performs I/O.

Signature: throws IOException

Wrong abstraction

The library lies. Borrowing an already-borrowed book reports that the book was not found.

IOException: Book not found: Dune
(after Dune was added and borrowed)

High — misleads debugging

Same conflation on return. The "or" in the message is the smell.

Book not found or not borrowed: Dune

Medium

Tier 2 — data loss and crashes

#	Defect	Evidence	Severity
D6	Unescaped separator destroys data. A `;` in a title silently shifts every field.	Saved: `Coming Home; A Novel` by `Rosamunde Pilcher` Reloaded: Coming Home by A Novel	Critical — silent corruption
D7	Failed load destroys the library. `books.clear()` runs before the file is opened.	1 book in memory, load a missing file → throws, and 0 books remain	Critical — data loss
D8	Parser trusts its input. `parts[2]` with no length check.	ArrayIndexOutOfBoundsException: Index 2 out of bounds for length 2	High
D9	Any non-digit at the menu kills the app — and the session’s work with it, since state is only saved on option 6.	InputMismatchException at Main.main(Main.java:72)	High
D10	A typo kills the app. `Main` catches `IOException` and rethrows as `RuntimeException`.	RuntimeException: java.io.IOException: Book not found: Gone With The Wind	High

Defect

Evidence

Severity

Unescaped separator destroys data. A ; in a title silently shifts every field.

Saved: Coming Home; A Novel by Rosamunde Pilcher
Reloaded: Coming Home by A Novel

Critical — silent corruption

Failed load destroys the library. books.clear() runs before the file is opened.

1 book in memory, load a missing file → throws, and 0 books remain

Critical — data loss

Parser trusts its input. parts[2] with no length check.

ArrayIndexOutOfBoundsException:
Index 2 out of bounds for length 2

High

Any non-digit at the menu kills the app — and the session’s work with it, since state is only saved on option 6.

InputMismatchException
at Main.main(Main.java:72)

High

D10

A typo kills the app. Main catches IOException and rethrows as RuntimeException.

RuntimeException: java.io.IOException:
Book not found: Gone With The Wind

High

Tier 3 — design and API

#	Defect	Note
D11	`searchBook` returns `null`.	Return `Optional<Book>`. Verified: returns literal `null` for an absent title.
D12	Dead `boolean` returns.	`borrowBook` can only return `true` — every other path throws.
D13	`Library` is also a file format.	Two reasons to change. Extract `LibraryRepository`; makes the Advanced SQLite tier additive.
D14	`Main` is untestable.	90-line `static` method, hardwired `System.in`/`System.out`, giant `switch`.
D15	Menu text duplicates the option constants.	A `MENU` string plus six `int` constants, kept in step by hand. Replace with an enum that renders the menu.
D16	No `equals`/`hashCode` on `Book`.	Verified: two books with identical title and author are not equal. Breaks `contains`, `remove`, and assertions on books.
D17	Menu constants are `public`.	On a `final` class with a private constructor. Nothing outside needs them.
D18	Title is the de facto identity.	So a library cannot hold two copies of one title. A genuine domain gap — name it in the README, do not build it.
D19	Prompt then newline.	`println(MENU)` where `MENU` ends `"Enter your choice: "`, so the cursor drops a line below the prompt.
D20	`scanner.close()` closes `System.in`.	Harmless at exit here, but a habit that breaks anything reading stdin later.

Defect

Note

D11

searchBook returns null.

Return Optional<Book>. Verified: returns literal null for an absent title.

D12

Dead boolean returns.

borrowBook can only return true — every other path throws.

D13

Library is also a file format.

Two reasons to change. Extract LibraryRepository; makes the Advanced SQLite tier additive.

D14

Main is untestable.

90-line static method, hardwired System.in/System.out, giant switch.

D15

Menu text duplicates the option constants.

A MENU string plus six int constants, kept in step by hand. Replace with an enum that renders the menu.

D16

No equals/hashCode on Book.

Verified: two books with identical title and author are not equal. Breaks contains, remove, and assertions on books.

D17

Menu constants are public.

On a final class with a private constructor. Nothing outside needs them.

D18

Title is the de facto identity.

So a library cannot hold two copies of one title. A genuine domain gap — name it in the README, do not build it.

D19

Prompt then newline.

println(MENU) where MENU ends "Enter your choice: ", so the cursor drops a line below the prompt.

D20

scanner.close() closes System.in.

Harmless at exit here, but a habit that breaks anything reading stdin later.

Tier 4 — build

#	Defect	Evidence
D21	`source`/`target` instead of `release`.	[WARNING] location of system modules is not set in conjunction with -source 11 --release 11 is recommended instead
D22	`<groupId>groupId</groupId>` — an unedited placeholder.	—
D23	`libraryState.txt` is not git-ignored and is written into the working directory.	—
D24	Checkstyle is declared under `<reporting>` only, with no `configLocation` — so it uses `sun_checks.xml` and runs only under `mvn site`.	Explains the `final` parameters and javadoc-on-everything style. Match it.

Defect

Evidence

D21

source/target instead of release.

[WARNING] location of system modules is not set in
conjunction with -source 11
--release 11 is recommended instead

D22

<groupId>groupId</groupId> — an unedited placeholder.

—

D23

libraryState.txt is not git-ignored and is written into the working directory.

—

D24

Checkstyle is declared under <reporting> only, with no configLocation — so it uses sun_checks.xml and runs only under mvn site.

Explains the final parameters and javadoc-on-everything style. Match it.

Not a defect — a constraint

The pom pins Java 11. That is not a bug to fix; it is a boundary to work inside. No records, no sealed types, no switch expressions, no text blocks, no Stream.toList(). Verified: javac --release 11 gives “records are not supported in -source 11”. JDK 25 still accepts --release 8, 11, 17, 21 and 25, so staying on 11 is safe on any assessor’s machine.

Reproduce them yourself

cd ~/Desktop/java-guild-candidate-test-intermediate-main export JAVA_HOME=$(/usr/libexec/java_home -v 25) ~/.local/maven/bin/mvn clean compile # D9 - a letter at the menu printf 'x\n' | "$JAVA_HOME/bin/java" -cp target/classes \ com.solirius.intermediate.library.Main # D10 - borrowing something absent printf '4\nGone With The Wind\n' | "$JAVA_HOME/bin/java" -cp target/classes \ com.solirius.intermediate.library.Main # D6 - the semicolon. Add the book, exit, restart, list. printf '1\nComing Home; A Novel\nRosamunde Pilcher\n6\n' | \ "$JAVA_HOME/bin/java" -cp target/classes com.solirius.intermediate.library.Main printf '2\n6\n' | "$JAVA_HOME/bin/java" -cp target/classes \ com.solirius.intermediate.library.Main rm -f libraryState.txt