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A Java virtual machine (JVM) is an abstract computing machine that enables a computer to run a Java program. There are three notions of the JVM: specification, implementation, and instance. The specification is a document that formally describes what is required of a JVM implementation. Having a single specification ensures all implementations are interoperable. A JVM implementation is a computer program that meets the requirements of the JVM specification. An instance of a JVM is an implementation running in a process that executes a computer program compiled into Java bytecode. The Oracle Corporation, which owns the Java trademark, distributes the Java Virtual Machine implementation HotSpot together with an implementation of the Java Class Library under the name Java Runtime Environment (JRE). ==JVM specification== The Java virtual machine is an abstract (virtual) computer defined by a specification. This specification omits implementation details that are not essential to ensure interoperability. For example, the memory layout of run-time data areas, the garbage-collection algorithm used, and any internal optimization of the Java virtual machine instructions (their translation into machine code). The main reason for this omission is to not unnecessarily constrain implementors. Any Java application can be run only inside some concrete implementation of the abstract specification of the Java virtual machine.〔Bill Venners, ''(Inside the Java Virtual Machine )'' Chapter 5〕 Starting with Java Platform, Standard Edition (J2SE) 5.0, changes to the JVM specification have been developed under the Java Community Process as JSR 924. , changes to specification to support changes proposed to the class file format (JSR 202) are being done as a maintenance release of JSR 924. The specification for the JVM was published as the ''blue book'',〔''(The Java Virtual Machine Specification )'' (the (first ) and (second ) editions are also available online).〕 The preface states: One of Oracle's JVMs is named HotSpot, the other, inherited from BEA Systems is JRockit. Clean-room Java implementations include Kaffe and IBM J9. Oracle owns the Java trademark, and may allow its use to certify implementation suites as fully compatible with Oracle's specification.. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Java virtual machine」の詳細全文を読む スポンサード リンク
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