The Core Libraries Group

This group is comprised of developers who participate in the design, implementation, and maintanence of the Java core libraries.

Introduction

The core libraries consist of classes which are used by many portions of the JDK. The actual set of files has evolved over time, but mostly they include functionality which is close to the VM and is not explicitly included in other areas, such as Security or Networking. Also included are commonly used tools which are either built on top of the core libraries (such as jar) or are used by developers working with them (such as rmic).

Feature Areas

The following table lists the feature areas of the core libraries with their corresponding repository locations and links to other developer documentation. (For documentation targeted for JDK users rather than contributors, see the section End-User Documentation.)

Currently there are some libraries which appear in the name packages as core libraries but are maintained by other groups. These exceptions are mentioned within the corresponding table entries.

Feature Area	Repository Locations	More Information
java.lang Provides classes that are fundamental to the design of the Java programming language such as String, Math, Enum, and the wrapper classes for primitive types (e.g. Boolean, Float, Character).	src/share/classes/java/lang src/share/native/java/lang src/solaris/classes/java/lang src/solaris/native/java/lang src/windows/classes/java/lang src/windows/native/java/lang test/java/lang make/java/java	Bugs
Threading Includes basic runtime support for threads.	src/share/classes/java/lang/Thread*.java src/share/native/java/lang/Thread.c test/java/lang/Thread* make/java/java	Bugs
Process Includes basic runtime support for creating processes and controlling process I/O.	src/share/classes/java/lang/Process.java src/share/classes/java/lang/ProcessBuilder.java src/share/classes/java/lang/Runtime.java src/share/native/java/lang/Runtime.c src/solaris/classes/java/lang/*Process* src/windows/classes/java/lang/*Process* src/solaris/native/java/lang/*Process* src/windows/native/java/lang/*Process* test/java/lang/ProcessBuidler test/java/lang/Runtime make/java/java	Bugs
java.lang.annotation Provides library support for the Java programming language annotation facility. (These are closely related to the Compiler API and javax.lang.model, which are owned by the Compiler Team.	src/share/classes/java/lang/annotation src/share/classes/sun/reflect/annotation	JSR 269— java.lang.annotation package added Bugs
java.lang.instrument Provides services that allow Java programming language agents to instrument programs running on the JVM. These APIs are owned by the Serviceability Team	src/share/classes/java/lang/instrument src/share/classes/sun/instrument src/share/instrument src/solaris/instrument src/windows/instrument test/java/lang/instrument make/java/instrument	See the Serviceability Team
java.lang.management Provides the management interface for monitoring and management of the JVM as well as the operating system on which the JVM is running. These APIs are owned by the Serviceability Team	src/share/classes/java/lang/management test/java/lang/management make/java/management	See the Serviceability Team
java.lang.ref Provides reference-object classes, which support a limited degree of interaction with the garbage collector.	src/share/classes/java/lang/ref src/share/native/java/lang/ref test/java/lang/ref make/java/java/	Bugs
java.lang.reflect Provides classes and interfaces for obtaining reflective information about classes and objects.	src/share/classes/java/lang/reflect src/share/classes/sun/reflect src/share/native/java/lang/reflect src/share/native/sun/reflect test/java/lang/reflect test/java/lang/Class make/java/java/reflect	Bugs
java.io Provides for system input and output and the file system.	src/share/classes/java/io src/share/native/java/io src/solaris/classes/java/io src/solaris/native/java/io src/windows/classes/java/io src/windows/native/java/io test/java/io make/java/java	Bugs
Serialization Supports encoding of objects to and from byte streams.	src/share/classes/java/io/Externalizable.java src/share/classes/java/io/ObjectInputStream.java src/share/classes/java/io/ObjectOutputStream.java src/share/classes/java/io/NotSerializableException.java src/share/classes/java/io/Serializable.java src/share/classes/java/io/SerializablePermission.java src/share/native/java/io/ObjectInputStream.c src/share/native/java/io/ObjectOutputStream.c test/java/io/Externalizable test/java/io/ObjectInputStream test/java/io/Serializable make/java/java	Java Object Serialization Specification Bugs
serialver Tool retrieves the serialVersionID for a class.	src/share/classes/sun/tools/serialver make/sun/serialver test/java/io/Serializable/serialver	Unix reference page Windows reference page
java.nio Provides buffers to contain data of primitive type.	src/share/classes/java/nio src/share/classes/sun/nio/ByteBuffered.java src/share/native/java/nio src/solaris/native/java/nio src/windows/native/java/nio test/java/nio/Buffer test/java/nio/ByteOrder test/java/nio/MappedByteBuffer make/java/nio	JSR 51— java.nio* packages added JSR 203—NIO enhancements under development Bugs
java.nio.channels java.nio.channels.spi Defines channels, an abstraction for devices capable of performing I/O operations; defines selectors for multiplexed, non-blocking I/O.	src/share/classes/java/nio/channels src/share/classes/sun/nio/ch src/share/native/sun/nio/ch src/share/sample/nio src/solaris/classes/sun/nio/ch src/solaris/native/sun/nio/ch src/windows/classes/sun/nio/ch src/windows/native/sun/nio/ch test/java/nio/channels test/sun/nio/ch make/java/nio src/share/sample/nio make/mksampel/nio	Channel bugs Selector bugs
java.nio.charset java.nio.charset.spi Defines charsets, decoders, and encoders, for translating between bytes and Unicode characters	src/share/classes/java/nio/charset src/share/classes/sun/nio/cs src/solaris/classes/sun/nio/cs make/java/nio	Supported Encodings Charset bugs Encoder/Decoder bugs
native2ascii Tool converts files to and from native encodings.	src/share/classes/sun/tools/native2ascii test/sun/tools/native2ascii make/sun/native2ascii	Unix reference page Windows reference page Bugs
java.util Provides the collections framework, formatted printing and scanning, array manipulation utilities, event model, date and time facilities, internationalization, and miscellaneous utility classes.	src/share/classes/java/util test/java/util make/java/java	Bugs
Collections Includes all classes which implement the Collection interface such as data structures implementing lists, queues, maps, and sets.	src/share/classes/java/util/ArrayDeque.java src/share/classes/java/util/ArrayList.java src/share/classes/java/util/Collection.java src/share/classes/java/util/Collections.java src/share/classes/java/util/*Map.java src/share/classes/java/util/*Set.java src/share/classes/java/util/Linked*.java src/share/classes/java/util/Stack.java src/share/classes/java/util/Vector.java test/java/util/ArrayDeque.java test/java/util/ArrayList.java test/java/util/Collection.java test/java/util/Collections.java test/java/util/*Map.java test/java/util/*Set.java test/java/util/Linked*.java test/java/util/Stack.java test/java/util/Vector.java make/java/java	Bugs
Internationalization Classes Includes support for internationalization and locale-specific output of dates, times, and currencies. These APIs are owned by the Internationalization Team	src/share/classes/java/util/*Calendar.java src/share/classes/java/util/Currency.java src/share/classes/java/util/Date.java src/share/classes/java/util/Locale*.java src/share/classes/java/util/ResourceBundle.java src/share/classes/java/util/*TimeZone*.java src/share/classes/sun/util/*.java (except PreHashedMap.java) src/share/classes/sun/util/resources make/java/java	See the Internationalization Team Bugs
java.util.concurrent java.util.concurrent.atomic java.util.concurrent.locks Provides utility classes used in concurrent programming, including support for atomic updates of single variables and a locking framework which supplements language-level synchronization.	src/share/classes/java/util/concurrent src/share/native/java/util/concurrent test/java/util/concurrent make/java/java	JSR 166— java.util.concurrent* packages added Maintainer's website Bugs
java.util.jar Provides classes for reading and writing the JAR (Java ARchive) file format.	src/share/classes/com/sun/java/util/jar src/share/classes/java/util/jar src/share/native/com/sun/java/util/jar test/java/util/jar make/java/jar Not strictly part of JAR, but useful: src/share/classes/sun/net/www/protocol/jar src/solaris/classes/sun/net/www/protocol/jar src/windows/classes/sun/net/www/protocol/jar test/sun/net/www/protocol/jar	JAR File Specification java.util.{jar,zip} Bugs jarsigner is owned by the Security Team
jar Tool creates and accesses the contents of a .jar file.	src/share/classes/sun/tools/jar test/tools/jar make/sun/jar	Unix reference page Windows reference page Bugs
extcheck Tool detects conflicts between a target .jar file and the currently installed extension .jar files.	src/share/classes/com/sun/tools/extcheck make/com/sun/extcheck	Unix reference page Windows reference page Bugs in the extension mechanism, including extcheck
java.util.logging Provides support to maintain and service software at customer sites.	src/share/classes/java/util/logging src/share/classes/sun/util/logging test/java/util/logging make/java/logging	Bugs
java.util.regex Provides classes for matching character sequences against patterns specified by regular expressions.	src/share/classes/java/util/regex make/java/java	Bugs
java.util.prefs Provides classes to store and retrieve user and system preference and configuration data.	src/share/classes/java/util/prefs src/solaris/classes/java/util/prefs src/windows/classes/java/util/prefs make/java/java	Bugs
java.util.spi Service provider classes for the java.util package. These APIs are owned by the Internationalization Team	src/share/classes/java/util/spi make/java/java	See the Internationalization Team
java.util.zip Provides classes for reading and writing the standard ZIP and GZIP file formats.	src/share/classes/java/util/zip src/share/native/java/util/zip make/java/zip test/java/util/zip	Bugs
java.math Provides classes for performing arbitrary-precision integer arithmetic (BigInteger) and arbitrary-precision decimal arithmetic (BigDecimal).	src/share/classes/java/math src/share/classes/java/lang/Math.java src/share/classes/java/lang/StrictMath.java src/share/classes/sun/misc/FloatConsts.java src/share/classes/sun/misc/FloatingDecimal.java make/java/math	JSR 13— BigDecimal enhancements Bugs
java.rmi java.rmi.activation java.rmi.dgc java.rmi.registry java.rmi.server Provides support for remote communication between programs written in Java.	src/share/classes/java/rmi src/share/classes/sun/rmi test/java/rmi test/sun/rmi make/java/rmi make/sun/rmi	Remote Invocation Home Page Java RMI Specification Bugs
rmic Tool generates stub, skeleton, and tie classes for remote objects using either the JRMP or IIOP protocols, and generates OMG IDL.	src/share/classes/java/rmi/rmic test/sun/rmi/rmic make/java/rmi/rmic make/sun/rmi/rmic	Unix reference page Windows reference page
rmid Tool starts the activation system daemon that allows objects to be registered and activated in a VM.	src/share/classes/com/sun/rmi/rmid make/sun/rmi/rmid	Unix reference page Windows reference page
rmiregistry Tool starts a remote object registry on the specified port on the current host.	src/share/classes/sun/rmi/registry make/sun/rmi/registry	Unix reference page Windows reference page
javax.naming javax.naming.directory javax.naming.event javax.naming.ldap javax.naming.spi Provides access to Naming and Directory Service such as DNS and LDAP.	src/share/classes/javax/naming src/share/classes/com/sun/naming test/javax/naming make/javax/naming src/share/classes/com/sun/jndi test/com/sun/jndi make/com/sun/jndi	Java Naming and Directory Interface Home Page Bugs
javax.script Provides interfaces and classes that define Java Scripting Engines and a framework for their use in Java applications. JDK 6 includes source code for the Mozilla Rhino javascript engine in src/share/classes/sun/org/mozilla/javascript. The .class files for this engine are in rt.jar. The source code has been removed from OpenJDK. In order to use scripting, a JSR 223 compatible scripting engine must be made available on the CLASSPATH.	src/share/classes/javax/script src/share/classes/com/sun/script src/share/demo/scripting/jconsole.plugin src/share/sample/scripting test/javax/script make/javax/script make/com/sun/script	JSR 223— scripting support A. Sundararajan's blog entry Mozilla Rhino: Java Script for Java Bugs— search "script" in synopsis
jrunscript Tool provides a command line script shell both both interactive and batch modes of script execution. This tool is experimental and unsupported.	src/share/classes/com/sun/tools/script test/sun/tools/jrunscript make/sun/jrunscript	Reference Page

Building

Developers are strongly encouraged to perform full builds prior to check-in of any changes. (A full build is a build performed when there is no pre-existing build directory; the workspace should contain only the desired changes and no auto-generated data. Simply performing make at the top of the build tree is not a full build.) Depending on the area, incremental builds are not a reliable indicator of whether or not changes will compile successfully in a full build. In particular, the contents of make/java/java are used early in the bootstrap phase to build components like java.lang.Object, the launcher, and javac that are used to build the rest of the JDK. These are later re-built once sufficient infrastructure has been generated by the bootstrap build. Incremental builds will only catch errors that occur in the compile after bootstrap.

Even when it appears that only java code is being modified, it is prudent to build on multiple platform families. A recommended minimum is one Windows and one Unix target, but depending on the code being modified, it may be necessary to include a wider spectrum or a specific set of platforms. This is necessary because there is no guarantee that the java code which depends on a change in core is identical on all platforms. For instance, rt.jar is not portable—the classes within it vary from platform to platform.

Testing

Tests or modifications of existing tests are required and must accompany all changes (both new functionality and any bug fixes). There are some exceptions. For example, it is not always possible to provide test for fixes for performance problems or other conditions that are difficult to simulate or require unusual environmental conditions (such as exceptionally low memory, system reboot, third-party software, etc.).

In addition to running the new tests, tests in the modified area and any dependent areas should be run. Dependent areas may not be immediately obvious. As with builds, it is necessary to run tests on multiple platforms.

Not all areas have tests in the repository. There are two possible reasons for this. It may be that there are no tests or tests may exist, but have not been audited for open-sourcing. In the latter case, the goal is to add them soon. Please ask about appropriate testing when considering a modification.

End-User Documentation

The following links reference the canonical end-user documentation for the JDK. The features areas listed above will have documentation in the corresponding sections of these references.

• JDK 6 Documentation
  The features areas listed above will have documentation in the corresponding sections of this reference which includes release notes describing the history of feature updates.
• The Java Tutorials
  The majority of core functionality is described in the section "Trails Covering the Basics". Additional topics may be found in the "Specialized Trails and Lessons" section.

Community

• Mailing lists
  • core-libs-dev

• Core libraries bloggers
  • Alan Bateman
    Specification Lead for JSR 203 - "More New I/O APIs for the Java Platform ("NIO.2")"
  • Joe Darcy
    Specification Lead for JSR 269 - "Pluggable Annotation Processing API" and Floating-point Czar
  • A. Sundararajan
    Implementation Lead for JSR 233 - "Scripting for the Java Platform" and a member of the Serviceability Team