java-final-keyword

Java final Keyword Conventions

When writing or modifying Java code in this project, apply final according to these conventions.

Method Parameters — Always final

Every method parameter must be final. This includes constructors, lambda parameters, and catch blocks.

public String download(final S3File file) { ... }
public static Token decrypt(final String base64Token) { ... }
public void upload(final String customerId, final LocalDate expiration) { ... }

Local Variables — Always final

Every local variable must be final. The only exception is a variable that is intentionally reassigned (e.g., a loop accumulator).

final LocalDate now = LocalDate.now();
final String[] parts = decrypted.split(":");
final File target = new File(destination, name);

Instance Fields — final for immutability

Fields in Lombok @Data/@Builder classes are final by default, producing immutable objects. Only omit final when the field must be mutable (e.g., a counter or state tracker).

@Data
@Builder(builderClassName = "Builder")
public class Download {
    private final File destination;   // immutable
    private final PrintStream out;    // immutable
    private int count;                // intentionally mutable
}

Static Fields — Always final

All static fields are constants and must be final.

private static final Logger LOGGER = Logger.getLogger(Signatures.class.getName());
private static final String ALGORITHM = "AES";

Enum Fields — Always final

Enum instance fields are always final, and enum constructor parameters follow the same rules as method parameters.

enum Action {
    DOWNLOAD("Downloading", "Downloaded");

    private final String presentProgressive;
    private final String past;

    Action(final String presentProgressive, final String past) {
        this.presentProgressive = presentProgressive;
        this.past = past;
    }
}

Class Declarations — Not typically final

Classes are generally not marked final. The exception is utility classes with only static methods.

Method Declarations — Not typically final

Methods are generally not marked final. This is not part of the project convention.