Java Class Library (JCL)
JCL is a collection of packages that implement the language. In simpler terms, it is a collection of the .class files that are included in the JDK and ready to be used. Once you have installed Java, you get them as part of the installation and can start building your application code up using the JCL classes as building blocks, which take care of a lot of the low-level plumbing. The richness and ease of use of JCL have substantially contributed to Java’s popularity.
To use a JCL package, you can import it without adding a new dependency to the pom.xml file. Maven adds JCL to the classpath automatically. And that is what separates the standard library and external libraries; if you need to add a library (typically, a .jar file) as a dependency in the Maven pom.xml configuration file, this library is an external one. Otherwise, it is a standard library or JCL.
Some JCL package names start with java. Traditionally, they are called core Java packages...
