Broadly speaking, Clojure, JRuby, Groovy, etc. running on language and its associated program on the Java virtual machine are all Java technology in a system. If only from the traditional point of view, Java technology, Sun officially defined system includes the following components: • Java programming language
• Java virtual machine on a variety of hardware platforms
• Class File Format
• Java API class libraries
• Third-party Java class libraries from the open source community and commercial organizations
Can the Java programming language, Java virtual machine, Java API class libraries these three parts collectively referred to as the JDK (Java Development Kit), the JDK for Java programs to support the development of a minimal environment,
Can the Java SE API subset of the Java API class libraries and the Java virtual machine two parts collectively referred to as the JRE (Java Runtime Environment), the JRE supports standard Java environment to run.
The following figure shows the contents of Java technology system included, as well as the scope of JDK and JRE covered.
These are to be divided according to the functions of the various components, according to the field of technology and services to divide, or in accordance with the key business areas of concern to divide Java technology, Java technology system can be divided into four platforms, namely:
• Java Card: Support some Java applets (Applets) running on the platform small memory devices (such as smart cards).
• Java ME (Micro Edition): supports the Java platform running on a mobile terminal (mobile phone, PDA), and on the Java API has been streamlined, and added support for mobile terminals, the version formerly known as J2ME.
• Java SE (Standard Edition): Support for the Java platform desktop applications (such as applications under Windows) offers a complete Java core API, this version formerly known as J2SE.
• Java EE (Enterprise Edition): supports the use of multi-tiered enterprise applications (such as ERP, CRM applications) Java platform, in addition to providing JavaSE API, but also a lot of its expansion and provides related deployment support, this version formerly known as J2EE.
Source: In-depth understanding of the Java virtual machine technology system 1.2Java