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. Although its syntax is similar to that of C and C++, the Java language has fewer low-level facilities than either of them. The Java runtime provides dynamic capabilities that are typically not available in traditional compiled languages.
A Java virtual machine (JVM) is a virtual machine that enables a computer to run Java programs as well as programs written in other languages that are also compiled to Java bytecode. The JVM is detailed by a specification that formally describes what is required in a JVM implementation. Having a specification ensures interoperability of Java programs across different implementations so that program authors using the Java Development Kit (JDK) need not worry about idiosyncrasies of the underlying hardware platform.
javac is the primary Java compiler included in the Java Development Kit (JDK) from Oracle Corporation. Martin Odersky implemented the GJ compiler, and his implementation became the basis for javac.
HotSpot, released as Java HotSpot Performance Engine, is a Java virtual machine for desktop and server computers, developed by Sun Microsystems which was purchased by and became a division of Oracle Corporation in 2010. Its features improved performance via methods such as just-in-time compilation and adaptive optimization. It is the de facto Java Virtual Machine, serving as the reference implementation of the Java programming language.
Apache Harmony is a retired open source, free Java implementation, developed by the Apache Software Foundation. It was announced in early May 2005 and on October 25, 2006, the board of directors voted to make Apache Harmony a top-level project. The Harmony project achieved 99% completeness for J2SE 5.0, and 97% for Java SE 6. The Android operating system has historically been a major user of Harmony, although since Android Nougat it increasingly relies on OpenJDK libraries.
In computing, Java Web Start is a deprecated framework developed by Sun Microsystems that allows users to start application software for the Java Platform directly from the Internet using a web browser. The technology enables seamless version updating for globally distributed applications and greater control of memory allocation to the Java virtual machine.
Apache Derby is a relational database management system (RDBMS) developed by the Apache Software Foundation that can be embedded in Java programs and used for online transaction processing. It has a 3.5 MB disk-space footprint.
Java is a set of computer software and specifications that provides a software platform for developing application software and deploying it in a cross-platform computing environment. Java is used in a wide variety of computing platforms from embedded devices and mobile phones to enterprise servers and supercomputers. Java applets, which are less common than standalone Java applications, were commonly run in secure, sandboxed environments to provide many features of native applications through being embedded in HTML pages.
The Java language has undergone several changes since JDK 1.0 as well as numerous additions of classes and packages to the standard library. Since J2SE 1.4, the evolution of the Java language has been governed by the Java Community Process (JCP), which uses Java Specification Requests (JSRs) to propose and specify additions and changes to the Java platform. The language is specified by the Java Language Specification (JLS); changes to the JLS are managed under JSR 901. In September 2017, Mark Reinhold, chief Architect of the Java Platform, proposed to change the release train to "one feature release every six months" rather than the then-current two-year schedule. This proposal took effect for all following versions, and is still the current release schedule.
OpenJDK is a free and open-source implementation of the Java Platform, Standard Edition. It is the result of an effort Sun Microsystems began in 2006. The implementation is licensed under the GPL-2.0-only with a linking exception. Were it not for the GPL linking exception, components that linked to the Java Class Library would be subject to the terms of the GPL license. OpenJDK is the official reference implementation of Java SE since version 7.
Comparison of the Java and .NET platforms.
IcedTea is a build and integration project for OpenJDK launched by Red Hat in June 2007. IcedTea also includes some addon libraries: IcedTea-Web is a free software implementation of Java Web Start and the Java web browser applet plugin. IcedTea-Sound is a collection of plugins for the Java sound subsystem, including the PulseAudio provider which used to be included with IcedTea. The Free Software Foundation recommends that all Java programmers use IcedTea as their development environment.
VisualVM is a tool that provides a visual interface for viewing detailed information about Java applications while they are running on a Java Virtual Machine (JVM). VisualVM organizes JVM data that is retrieved by the Java Development Kit (JDK) tools and presents the information in a way that allows data on multiple Java applications to be quickly viewed—both local applications and applications that are running on remote hosts. Programmers can also capture data about the JVM software and save the data to the local system, and then view the data later or share it with others. VisualVM is built on the NetBeans Platform; its architecture is modular and easy to extend with plugins.
Oracle WebLogic Server is a Java EE application server currently developed by Oracle Corporation. Oracle acquired WebLogic Server when it purchased BEA Systems in 2008.
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 Java virtual machine, a compiler, performance monitoring tools, a debugger, and other utilities that Oracle considers useful for Java programmers.
Nashorn is a JavaScript engine developed in the Java programming language originally by Oracle and later by the OpenJDK Community. It relies on the support for dynamically typed languages on the Java Platform Nashorn has been included with Java 8 through JDK 14.
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. This allows for faster initialization, greater runtime performance, and decreased resource consumption, but the resulting executable can only run on the platform it was compiled for.
JDK Flight Recorder is an event recorder built into the OpenJDK Java virtual machine. It can be thought of as the software equivalent of a Data Flight Recorder in a commercial aircraft. It captures information about the JVM itself, and the application running in the JVM. There is a wide variety of data captured, for example method profiling, allocation profiling and garbage collection related events. The JDK Flight Recorder was designed to minimize the Observer Effect in the profiled system, and is meant to be always on in production systems. The technology was open sourced in 2018.
