In computer science, garbage collection (GC) is a form of automatic memory management. The garbage collector attempts to reclaim memory which was allocated by the program, but is no longer referenced; such memory is called garbage. Garbage collection was invented by American computer scientist John McCarthy around 1959 to simplify manual memory management in Lisp.
Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let programmers write once, run anywhere (WORA), meaning that compiled Java code can run on all platforms that support Java without the need to recompile. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but has fewer low-level facilities than either of them. The Java runtime provides dynamic capabilities that are typically not available in traditional compiled languages.
GNU Classpath is a free software implementation of the standard class library for the Java programming language. Most classes from J2SE 1.4 and 5.0 are implemented. Classpath can thus be used to run Java-based applications. GNU Classpath is a part of the GNU Project. It was originally developed in parallel with libgcj due to license incompatibilities, but later the two projects merged.
Embedded Java refers to versions of the Java program language that are designed for embedded systems. Since 2010 embedded Java implementations have come closer to standard Java, and are now virtually identical to the Java Standard Edition. Since Java 9 customization of the Java Runtime through modularization removes the need for specialized Java profiles targeting embedded devices.
HotSpot, released as Java HotSpot Performance Engine, is a Java virtual machine for desktop and server computers, developed by Sun Microsystems and now maintained and distributed by Oracle Corporation. It features improved performance via methods such as just-in-time compilation and adaptive optimization.
JamVM is an open-source Java Virtual Machine (JVM) developed to be extremely small compared with other virtual machines (VMs) while conforming to the Java virtual machine specification version 2.
Java Card is a software technology that allows Java-based applications (applets) to be run securely on smart cards and more generally on similar secure small memory footprint devices which are called "secure elements" (SE). Today, a secure element is not limited to its smart cards and other removable cryptographic tokens form factors; embedded SEs soldered onto a device board and new security designs embedded into general purpose chips are also widely used. Java Card addresses this hardware fragmentation and specificities while retaining code portability brought forward by Java.
Jikes Research Virtual Machine is a mature virtual machine that runs programs written for the Java platform. Unlike most other Java virtual machines (JVMs), it is written in the programming language Java, in a style of implementation termed meta-circular. It is free and open source software released under an Eclipse Public License.
Real-time Java is a catch-all term for a combination of technologies that enables programmers to write programs that meet the demands of real-time systems in the Java programming language.
The Extensible Embeddable Language (EEL) is a scripting and programming language in development by David Olofson. EEL is intended for scripting in realtime systems with cycle rates in the kHz range, such as musical synthesizers and industrial control systems, but also aspires to be usable as a platform independent general purpose programming language.
Eclipse OpenJ9 is a high performance, scalable, Java virtual machine (JVM) implementation that is fully compliant with the Java Virtual Machine Specification.
Dalvik is a discontinued process virtual machine (VM) in the Android operating system that executes applications written for Android. Dalvik was an integral part of the Android software stack in the Android versions 4.4 "KitKat" and earlier, which were commonly used on mobile devices such as mobile phones and tablet computers, and more in some devices such as smart TVs and wearables. Dalvik is open-source software, originally written by Dan Bornstein, who named it after the fishing village of Dalvík in Eyjafjörður, Iceland.
The JamaicaVM is a virtual machine and build environment for developing and running realtime Java programs. It includes a deterministic garbage collector and implements the RTSJ. It is designed for use in both realtime and embedded systems. It provides the base runtime environment for JamaicaCAR.
The Java Development Kit (JDK) is a distribution of Java Technology by Oracle Corporation. It implements the Java Language Specification (JLS) and the Java Virtual Machine Specification (JVMS) and provides the Standard Edition (SE) of the Java Application Programming Interface (API). It is derivative of the community driven OpenJDK which Oracle stewards. It provides software for working with Java applications. Examples of included software are the virtual machine, a compiler, performance monitoring tools, a debugger, and other utilities that Oracle considers useful for a Java programmer.
VeriFlux is a formal methods based static analysis tool for programs written in Java. It is optimized for use with JamaicaVM, but can be used for any Java program. It can detect uncaught runtime exceptions, including RTSJ exceptions, and possible deadlocks in code using Java synchronization features. It has also been used for resource analysis. It can be used for both full program analysis and partial program analysis.
Excelsior JET is a now-defunct proprietary Java SE technology implementation built around an ahead-of-time (AOT) Java to native code compiler. The compiler transforms the portable Java bytecode into optimized executables for the desired hardware and operating system (OS). Also included are a Java runtime featuring a just-in-time (JIT) compiler for handling classes that were not precompiled for whatever reason, the complete Java SE API implementation licensed from Oracle, and a toolkit to aid deployment of the optimized applications. Excelsior JET was developed by Excelsior LLC, headquartered in Novosibirsk, Russia.
GraalVM is a Java Development Kit (JDK), written in Java. The open-source distribution of GraalVM is based on OpenJDK, and the enterprise distribution is based on Oracle JDK. As well as just-in-time (JIT) compilation, GraalVM can compile a Java application ahead-of-time so that it starts instantly, provides peak performance with no warmup, and uses fewer resources. It provides additional programming languages and execution modes. The first production-ready release, GraalVM 19.0, was distributed in May 2019. The most recent release is GraalVM for JDK 21, made available in September 2023.
