Package

A package is a namespace that groups related classes. It prevents name collisions — two classes named Logger can coexist if they live in different packages. Packages are declared with the package keyword at the top of a source file.

Declaring and using

// File: src/com/example/util/StringUtils.java
package com.example.util;

public class StringUtils { ... }

// Using it from another package:
import com.example.util.StringUtils;

public class App {
    public static void main(String[] args) {
        StringUtils.trim("  hi  ");
    }
}

Package naming conventions

• Always lowercase: com.example.util, never com.Example.Util.
• Reverse-domain prefix: if your domain is example.com, packages start with com.example.
• The package hierarchy maps 1:1 to directory structure on disk.

Package-private visibility

A class or member with no access modifier (no public, protected, private) is visible only within its own package. This is called package-private or default access.

Packages vs modules

Packages are Java's oldest organisation unit. Since Java 9, modules add a higher-level grouping: a module contains one or more packages and explicitly declares what it exports to other modules.