Java Class Library

Overview

The Java Class Library (JCL) is a set of dynamically loadable libraries that Java applications can call at run time. Because the Java Platform is not dependent on a specific operating system, applications cannot rely on any of the platform-native libraries. Instead, the Java Platform provides a comprehensive set of standard class libraries, contained in the Java Class Library, as well as a few other standard libraries Java SE.

A collection of Java books, symbolizing the Java Class Library.

Structure

The Java Class Library is a set of packages that provide a common interface for writing Java programs. The library is divided into multiple packages, each of which contains a set of related classes and interfaces. These packages are grouped into modules, which can be individually loaded as needed by a Java application. This modular structure allows for efficient use of system resources and promotes code reuse JPMS.

Core Packages

The core packages of the Java Class Library cover the fundamental aspects of programming in Java. These include:

java.lang: Contains classes that are fundamental to the design of the Java programming language. This package is automatically imported into every Java program java.lang.
java.util: Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes java.util.
java.io: Provides for system input and output through data streams, serialization and the file system java.io.
java.net: Provides the classes for implementing networking applications java.net.
java.math: Provides classes for performing arbitrary-precision integer arithmetic (BigInteger) and arbitrary-precision decimal arithmetic (BigDecimal) java.math.

GUI Packages

The Java Class Library includes several packages for designing graphical user interfaces. The most commonly used of these are:

java.awt: The Abstract Window Toolkit (AWT) includes a large number of classes for creating user interfaces and for painting graphics and images java.awt.
javax.swing: Swing is a GUI widget toolkit for Java. It is part of Oracle's Java Foundation Classes (JFC) — an API for providing a graphical user interface (GUI) for Java programs javax.swing.

Database Packages

The Java Class Library provides packages for interacting with databases. These include:

java.sql: Provides the API for accessing and processing data stored in a data source, usually a relational database java.sql.
javax.sql: Provides the API for server-side data source access and processing from the Java programming language javax.sql.

Conclusion

The Java Class Library provides a comprehensive set of functionalities that are commonly used in Java programming. These range from basic language support and object-oriented programming to networking and I/O operations. The extensive class library is one of the reasons why Java is such a popular language for both new and experienced programmers.