The Java Class Library (JCL) is a set of dynamically loadable libraries

that Java Virtual Machine (JVM) languages 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, containing the functions common to modern

operating systems. Since Java 9, the Java Class Library can be accessed

through module path using the Java Platform Module System.

JCL serves three purposes within the JVM:

• Like other standard code libraries, they provide the programmer a

well-known set of useful facilities, such as container classes and

regular expression processing.

• The library provides an abstract interface to tasks that would

normally depend heavily on the hardware and operating system, such as

network access and file access.

• Some underlying platforms may not support all of the features a Java

application expects. In these cases, the library implementation can

either emulate those features or provide a consistent way to check for

the presence of a specific feature.