Java is a mature, powerful, industrial-grade, and extremeliy popular programming language with a rich, extensive, and well-written standard library as well as a plethora of opensource libraries for additional, readily reusable functionality. Java may be found in everything from native phone applications to server software running in the Cloud.

• Commonly used for
  • Android applications
  • servers
  • commandline applications
  • web applications (server-side logic)
  • data processing pipelines
  • desktop GUIs
  • web crawling
  • database interoperation / querying
  • others
• Rarely used for
  • web app UIs (possible with GWT, but not particularly common or recommended)
  • iOS apps (parts can be written in Java by using j2objc, but Obj-C or Swift is preferred/needed for iOS apps)
  • OS kernels (infeasible on typical hardware or without significant, non-standard extensions/modifications to the language)
  • drivers
  • other systems software
• Execution and distribution
  • bytecode compiled; ordinarily, code is translated to platform-independent byte code, which is distributed to all target CPU architectures; this bytecode is then just-in-time (JIT) or ahead-of-time (AOT) compiled to native instructions for the given target architecture such that there may be a mix of code that is executed directly by the CPU and bytecode that is executed indirectly by a program called an "interpreter" or "virtual machine"
• Memory management
  • automatic (garbage collected)

• The Java Tutorials for the official tutorials on the Java programming language
• Java 7 API for the standard library reference
• Android API Reference for the libraries provided on Android
• Google App Engine Java for writing a web server in Java on App Engine

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