Packages and Access Control

Packages provide namespaces and a visibility boundary. The source directory normally mirrors the package name. Imports shorten type references at compile time; they do not load code or include files.

Organizing an API

package com.example.orders;

import java.time.Instant;
import static java.util.Objects.requireNonNull;

public record Order(String id, Instant createdAt) {
    public Order {
        requireNonNull(id);
        requireNonNull(createdAt);
    }
}

Use reversed-domain names to avoid collisions. Wildcard imports do not include subpackages and can make name sources less obvious. Package-private types and members form an internal implementation surface; public types are long-lived contracts. The classpath locates unnamed-module classes and resources, while the module path resolves named modules. Avoid split packages across libraries and keep dependencies flowing from stable APIs toward replaceable implementations.