The usage of Java packages.

How Java packages organize code, prevent name collisions, and enforce access control.

Java packages act as a logical folder structure for your source code—java.lang, java.util, or a custom com.mycompany.util. They group related classes and sub-packages, making a large project modular and easy to navigate. Crucially, they provide a unique namespace that prevents naming conflicts: you can have your own Date class without clashing with java.util.Date because each sits in a different package. 

Beyond organization, the default package-private access level is a simple yet effective encapsulation feature. Any field or method declared without a modifier (public, protected, private) is visible only within the exact same package. This lets you hide internal helpers and data from outside code, protecting implementation details and ensuring that only authorized classes (those in the same package) can interact with sensitive members.