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Java performance
In software development, the Java programming language was historically considered slow〔http://www.scribblethink.org/Computer/javaCbenchmark.html〕 because compiled Java programs run on the Java Virtual Machine rather than directly on the computer's processor like C and C++ programs do. However, in newer Java versions the execution performance has been optimized significantly mainly thanks to the introduction of just-in-time compilation. Java performance is a matter of concern because lots of business software has been written in Java after the language quickly became popular in the late 1990s and early 2000s. Concerns over its performance led to the development of specialized hardware able to run Java directly, dubbed Java processors.
The performance of a compiled Java program depends on how optimally its particular tasks are managed by the host Java Virtual Machine (JVM), and how well the JVM takes advantage of the features of the hardware and OS in doing so. Thus, any Java performance test or comparison has to always report the version, vendor, OS and hardware architecture of the used JVM. In a similar manner, the performance of the equivalent natively compiled program will depend on the quality of its generated machine code, so the test or comparison also has to report the name, version and vendor of the used compiler, and its activated optimization directives.
Historically, the execution speed of Java programs improved significantly due to the introduction of Just-In Time compilation (JIT) (in 1997/1998 for Java 1.1),〔 the addition of language features supporting better code analysis, and optimizations in the JVM itself (such as HotSpot becoming the default for Sun's JVM in 2000). Hardware execution of Java bytecode, such as that offered by ARM's Jazelle, can also offer significant performance improvements.
==Virtual machine optimization techniques==
Many optimizations have improved the performance of the JVM over time. However, although Java was often the first Virtual machine to implement them successfully, they have often been used in other similar platforms as well.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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