Java Packages

A package in Java is a mechanism to group related classes, interfaces, and sub-packages into a single unit. Packages help organize large applications, avoid naming conflicts, provide access protection, and make code modular and maintainable.

• Avoiding name conflicts (two classes with the same name can exist in different packages)
• Providing access control using public, protected, and default access
• Reusability: packaged code can be imported and used anywhere
• Encouraging modular programming

Types of Java Packages

1. Built-in Packages

Built-in Packages comprise a large number of classes that are part of the Java API. Some of the commonly used built-in packages are:

• java.lang: Contains language support classes(e.g, classes that define primitive data types, math operations). This package is automatically imported.
• java.io: Contains classes for supporting input/output operations.
• java.util: Contains utility classes that implement data structures such as Linked Lists and Dictionaries, as well as support for date and time operations.
• java.applet: Contains classes for creating Applets.
• java.awt: Contains classes for implementing the components for graphical user interfaces (like buttons, menus, etc). 6)

Example: Using java.util.Random (Built-in Package)

Random number: 59

2. User-defined Packages

User-defined Packages are the packages that are defined by the user.

Example:

To use it in another class:

Forder Structure

Accessing Classes Inside a Package

In Java, we can import classes from a package using either of the following methods:

1 Import a Single Class

import java.util.Vector;

This imports only the Vector class from the java.util package.

2. Import all classes from a package:

import java.util.*;

This imports all classes and interfaces from the java.util package but does not include sub-packages.

Example: Import the Vector class

[3, 5, 7]

Access Modifiers and Packages

Packages directly influence Java access levels: