|Developer(s)||Oracle Corporation (previously Sun Microsystems)|
|Type||Java Virtual Machine|
|License||Proprietary (early versions), GNU General Public License (current)|
|Website||Sun's OpenJDK Hotspot page|
HotSpot, released as the "Java HotSpot Performance Engine" is a Java virtual machine for desktops and servers, maintained and distributed by Oracle Corporation. It features techniques such as just-in-time compilation and adaptive optimization designed to improve performance.
The Java HotSpot Performance Engine, first released April 27, 1999, was based on technologies from the Strongtalk implementation of the Smalltalk programming language originally developed by Longview Technologies, LLC which was doing business as Animorphic. Animorphic's virtual machine technology had earlier been successfully used in a Sun research project, the Self programming language. In 1997, Animorphic was purchased by Sun Microsystems.[not in citation given]
Shortly after acquiring Animorphic, Sun intended to write a new just-in-time (JIT) compiler for the newly developed virtual machine. This new compiler would be the source of the name "HotSpot", which derives from the fact that as it runs Java bytecode, it continually analyzes the program's performance for "hot spots" which are frequently or repeatedly executed. These are then targeted for optimization, leading to high performance execution with a minimum of overhead for less performance-critical code. In some cases, it is possible for adaptive optimization of a JVM to exceed the performance of hand-coded C++ or C code.
Sun's JRE features two virtual machines, one called Client and the other Server. The Client version is tuned for quick loading. It makes use of interpretation. The Server version loads more slowly, putting more effort into producing highly optimized JIT compilations, that yield higher performance. Both VMs compile only often-run methods, using a configurable invocation-count-threshold to decide which methods to compile.
- A class loader,
- A bytecode interpreter,
- Client and Server virtual machines, optimized for their respective uses
- Several garbage collectors,
- A set of supporting runtime libraries.
JVM flags 
HotSpot supports many command-line arguments for options of the virtual machine execution. Some are standard and must be found in any conforming Java virtual machine, others are specific to HotSpot and may not be found in other JVMs (options that begin with -X or -XX are non-standard).
Supported platforms 
Maintained by Oracle 
As for the whole JDK, HotSpot is supported by Oracle Corporation on Microsoft Windows, Linux, Solaris, and Mac OS X. Supported ISAs are IA-32, x86-64, ARMv6, ARMv7, and SPARC (exclusive to Solaris).
Ports by third parties 
Porting HotSpot is difficult because the code, while primarily written in C++, contains a lot of assembly language. To remedy this, the IcedTea project has developed a generic port of the HotSpot interpreter called zero-assembler Hotspot (or zero), with almost no assembly code. This port is intended for easy adaptation of the interpreter component of HotSpot to any Linux processor architecture. The code of zero-assembler Hotspot is used for all the non-x86 ports of HotSpot (PPC, IA64, S390 and ARM) since version 1.6.
See also 
- List of Java virtual machines
- Comparison of Java virtual machines
- Java performance
- Da Vinci Machine, a starting Sun project aiming to prototype the extension of the JVM to add support for dynamic languages
- Java Virtual Machine heap
- Comparison of application virtual machines
- "Sun Announces Availability of the Java HotSpot Performance Engine". Press Release. Sun Microsystems. Retrieved 26 March 2013.
- "Sun's Gosling Previews Hotspot Java Virtual Machine". ComputerGram. 1998-02-13. Retrieved 2008-04-20.[dead link]
- "Cliff Click on Azul's Pauseless GC, Zing, JVM Languages". InfoQ. 2011-01-20. Retrieved 2012-07-11.
- Lewis, J.P. (2004). "Performance of Java versus C++". Retrieved 2007-10-03.
- Shankland, Stephen (18 February 1999). "HotSpot finally makes its mark". Cnet. Retrieved 6 December 2012.
- "Sun Microsystems releases fastest client-side Java platform to date". Sun Microsystems. 2000-05-08. Retrieved 2007-10-03.
- "The HotSpot Group". Sun Microsystems. 2007. Retrieved 2007-10-03. "There are nearly 1500 C/C++ header and source files, comprising almost 250,000 lines of code"
- "Java HotSpot VM Options". Sun Microsystems. Retrieved 2009-02-08.
- Mocker, Joseph D. (2007-08-28). "A Collection of JVM Options". Archived from the original on 2011-04-30. Retrieved 2009-02-08.
- Maximovich, Dmitri. "The most complete list of -XX options for Java 6 JVM". Archived from the original on 2010-01-30. Retrieved 2009-02-08.
- Nutter, Charles (2009-01-29). "My Favorite Hotspot JVM Flags". Retrieved 2009-02-08.
- "Sun Opens Java". Sun Microsystems. 2006-11-13. Retrieved 2007-10-03.
- JDK7, Sun.
- "Supported System Configurations". Oracle Corporation. Retrieved 2012-01-06.
- Gary, Benson (2007-11-06). "Gary's guide to porting IcedTea". Retrieved 2008-01-26.
- Gary, Benson (2008-02-01). "1st February 2008". Retrieved 2008-02-03.
- Andrew, Haley (2008-01-31). "Making zero-assembler the default on ppc". Retrieved 2008-02-03.
- Lilian, Angel (2008-02-13). "IcedTea 1.6 Released with Zero-assembler and JNLP support!". Red Hat. Retrieved 2008-02-13.
- Sun's OpenJDK Hotspot page
- A list of HotSpot VMOptions
- The Java Virtual Machine Specification
- The history of the original Strongtalk/HotSpot team
- Sun announces availability of the Java Hotspot Performance Engine[dead link]