taoidle / java-best-practices

Name: taoidle/java-best-practices
Author: taoidle

Java coding best practices. Use when writing or reviewing Java code (17+). Covers modern features, error handling, and patterns.

Version

SKILL.md

2.0 KB

Java Best Practices (17+)

Code Style

Rule	Guideline
Formatter	`google-java-format`
Analysis	SpotBugs, Error Prone
Naming	Clear, no abbreviations

Modern Features

Feature	Usage
Records	Immutable data carriers
Sealed classes	Restricted hierarchies
Pattern matching	`instanceof` with binding
`var`	Local type inference

public record User(String id, String name) {}

if (obj instanceof String s && !s.isEmpty()) { process(s); }

public sealed interface Result<T> permits Success, Failure {}
record Success<T>(T value) implements Result<T> {}
record Failure<T>(Exception error) implements Result<T> {}

Error Handling

Rule	Guideline
Specific exceptions	Not bare `Exception`
Try-with-resources	For `AutoCloseable`

try (var reader = new BufferedReader(new FileReader(path))) {
    return reader.lines().toList();
} catch (IOException e) {
    throw new ConfigException("Failed: " + path, e);
}

Project Structure

src/main/java/com/example/{domain,service}/
src/test/java/
pom.xml or build.gradle

Common Patterns

Pattern	Usage
Optional	Null-safe returns
Stream API	Functional collections
Builder	Complex construction

public Optional<User> findById(String id) {
    return Optional.ofNullable(users.get(id));
}

Anti-Patterns

Avoid	Use Instead
Returning null	`Optional<T>`
Mutable data	Records
`instanceof` chains	Pattern matching

Testing (JUnit 5 + AssertJ)

@Test void shouldProcess() {
    var service = new Service(mockRepo);
    var result = service.process(input);
    assertThat(result.status()).isEqualTo(SUCCESS);
}