Java Class Library

JCL is almost entirely written in Java, except for the parts that need direct access to the hardware and operating system (such as for I/O or bitmap graphics), which are instead written in C++. The classes that give access to these functions commonly use Java Native Interface wrappers to access operating system APIs. Almost all of JCL is stored in a single Java archive file called "" which is provided with JRE and JDK distributions. The Java Class Library () is located in the default bootstrap classpath and does not have to appear in the classpath declared for the application. The runtime uses the bootstrap class loader to find the JCL. The Java Module System (part of the Java 9 release) broke the monolithic "" JAR file and modularized the JCL itself in several modules with specified dependencies. ==Conformance==

Any Java implementation must pass the Java Technology Compatibility Kit tests for compliance, which includes JCL tests. ==Main features==

JCL Features are accessed through classes provided in packages. • contains fundamental classes and interfaces closely tied to the language and runtime system. • I/O and networking access the platform file system, and more generally networks through the , and packages. For networking, SCTP is available through . • Mathematics package: provides mathematical expressions and evaluation, as well as arbitrary-precision decimal and integer number datatypes. • Collections and Utilities : built-in Collection data structures, and utility classes, for regular expressions, concurrency, logging and data compression. • GUI and 2D Graphics: the AWT package () basic GUI operations and binds to the underlying native system. It also contains the 2D Graphics API. The Swing package () is built on AWT and provides a platform-independent widget toolkit, as well as a pluggable look and feel. It also deals with editable and non-editable text components. • Sound: interfaces and classes for reading, writing, sequencing, and synthesizing of sound data. • Text: deals with text, dates, numbers and messages. • Image package: and provide APIs to write, read, and modify images. • XML: SAX, DOM, StAX, XSLT transforms, XPath and various APIs for Web services, as SOAP protocol and JAX-WS. • Security is provided by and encryption services are provided by . • Databases: access to SQL databases via • Access to Scripting engines: The package gives access to any conforming Scripting language. • Applets: allows applications to be downloaded over a network and run within a guarded sandbox • Java Beans: provides ways to manipulate reusable components. • Introspection and reflection: [https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Class.html ] represents a class, but other classes such as Method and Constructor are available in . Packages outside of the main namespace Java bundles some packages outside of the main namespaces (java.*, javax.*, and jdk.*). Among these include: • com.sun.*: some internal packages originally developed by Sun Microsystems, for HotSpot VM, abstract syntax tree, Java Debug Interface, and HTTP servers. • netscape.javascript.*: classes for accessing the JavaScript engine and HTML DOM in the web browser. Deprecated in Java 24, for eventual moving to JavaFX. • org.ietf.jgss.*: Generic Security Service API as specified by the Internet Engineering Task Force. • org.omg.*: Object Management Group packages, such as Common Object Request Broker Architecture (CORBA) features. Deprecated since Java 9, removed since Java 11. • org.w3c.dom.*: Document Object Model packages as specified by the World Wide Web Consortium. • org.xml.sax.*: Simple API for XML packages related to XML. Implementation packages The sun.* (which contains the sun.misc.Unsafe class, used to manipulate the CPU and hardware, directly manage memory, and other things) and other com.sun.* packages are all part of a module called jdk.unsupported. This module contains packages not part of the Java standard library but bundled as part of the Java implementation. ==Licensing==

Prior licenses Before the release of OpenJDK, the JDK was based on a proprietary license. Following their promise to release a fully buildable JDK based on almost completely free and open-source code in the first half of 2007, Sun released the complete source code of the Class Library under the GPL on May 8, 2007, except some limited parts that were licensed by Sun from third parties who did not want their code to be released under an open-source license. Sun's goal was to replace the parts that remain proprietary and closed source with alternative implementations and make the Class Library completely free and open source. Until December 2010, the remaining encumbered part of the JDK was made available by Sun then Oracle as Binary Plugs which were required to build the JDK but not necessary to run it. , the only part of the Class library that remained proprietary and closed-source (4% for OpenJDK 7, and less than 1% and OpenJDK 6) was the SNMP implementation. Since the first May 2007 release, Sun, with the help of the community, released as open-source or replaced with open-source alternatives almost all the encumbered code: • All the audio engine code, including the software synthesizer, became open source. The closed-source software synthesizer has been replaced by a new synthesizer developed specifically for OpenJDK called Gervill. • All cryptography classes were released as open-source. • The code that scales and rasterizes fonts uses open source FreeType. • The native color management uses open-source LittleCMS. • The JavaScript plugin is open source (the JavaScript engine itself was open source from the beginning). Open source release Beginning in December 2010, all the so-called binary plugs were replaced by open source replacements, making the entire JDK open. ==Alternative implementations==

GNU Classpath is the other main free software class library for Java. Contrary to other implementations, it only implements the Class Library, and is used by many free Java runtimes (like Kaffe, SableVM, JamVM). Apache Harmony was another free software class library. Its aim was to implement the other parts of the Java stack (Virtual Machine, Compiler, and other tools required for any Java implementation). ==See also==