Quick Reference · Claude Code for Java Developers

Commands & shortcuts

You type	What it does
`claude`	Start an interactive session in the current directory
`claude -p "…"`	Headless: run one prompt non-interactively and print the result (scriptable in CI)
`claude --version`	Print the installed version
`/help`	List available commands
`/init`	Generate a starter `CLAUDE.md` from your project
`/clear`	Start a fresh conversation (do this between unrelated tasks)
`/login`	Switch between subscription and API-key auth
`/permissions`	View and edit permission rules
`/config`	Open settings
`@path/to/File.java`	Reference a file or directory so Claude reads exactly that
`!mvn test`	Run a shell command and feed its output into the conversation
`Shift+Tab`	Cycle permission modes: default → accept-edits → plan
`Esc`	Interrupt the current turn to correct course
“think” / “think hard”	Ask Claude to reason longer before acting

Permission rule patterns

Rules live in settings.json under permissions. The :* suffix matches any trailing arguments.

{
  "permissions": {
    "allow": ["Bash(./gradlew test:*)", "Bash(mvn verify:*)"],
    "ask":   ["Bash(./gradlew publish:*)", "Bash(git push:*)"],
    "deny":  ["Bash(rm:*)"]
  }
}

allow — safe, locally reversible: compile, test, format.
ask — anything that reaches the outside world: publish, push, deploy.
deny — defense-in-depth, not a security boundary. You reviewing every command is the real protection.

Where configuration lives

File	Scope	Commit it?
`~/.claude/settings.json`	Your settings, all projects	No (it’s yours)
`~/.claude/CLAUDE.md`	Your personal preferences, all projects	No
`.claude/settings.json`	Project settings (build allow-list, hooks)	Yes — shared with the team
`.claude/settings.local.json`	Your personal project overrides	No — git-ignore it
`./CLAUDE.md`	Project memory (build commands, conventions, gotchas)	Yes
`.claude/commands/*.md`	Custom slash commands	Yes (shared vocabulary)
`.claude/skills/<name>/SKILL.md`	Skills Claude reaches for on its own	Yes
`.claude/agents/*.md`	Specialized subagents	Yes

JUnit 4 → 5 migration map

The conversion most Java teams hit during a Spring Boot 3 upgrade (Module 6). Most rows are mechanical — the last two are not.

JUnit 4	JUnit 5 (Jupiter)
`org.junit.Test`	`org.junit.jupiter.api.Test`
`@Before` / `@After`	`@BeforeEach` / `@AfterEach`
`@BeforeClass` / `@AfterClass`	`@BeforeAll` / `@AfterAll` (static)
`@Ignore`	`@Disabled`
`@Test(expected = X.class)`	`assertThrows(X.class, () -> …)`
`@Test(timeout = 100)`	`assertTimeout(Duration.ofMillis(100), …)`
`@RunWith(SpringRunner.class)`	`@ExtendWith(SpringExtension.class)` or `@SpringBootTest`
`@RunWith(MockitoJUnitRunner.class)`	`@ExtendWith(MockitoExtension.class)`
`@Category`	`@Tag`
`org.junit.Assert.*`	`org.junit.jupiter.api.Assertions.` — message argument moves to last*
`@Rule` / `@ClassRule`	No equivalent — restructure (e.g. Testcontainers `@Container`, `@TempDir`)

Two traps: the Assertions methods take the optional failure message as the last parameter, the reverse of JUnit 4 — easy to flip silently. And @Rule/@ClassRule have no annotation swap; they must be re-expressed (Testcontainers and TemporaryFolder are the usual culprits). Tell a migrating agent to flag these rather than guess.

Spring Boot 2.7 → 3.x landmarks

Java 17 is the hard minimum. Raise the JDK first or nothing compiles.
javax.* → jakarta.* across persistence, validation, servlet APIs.
Spring Security: WebSecurityConfigurerAdapter is removed → SecurityFilterChain beans.
Auto-configuration registration: spring.factories → META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports.
Hibernate 5 → 6: dialect and mapping changes that can alter runtime behaviour — pin it with characterization tests.

Back to the curriculum, or start at Module 1.