Java Virtual Machine

The heart of the Java Platform is the common processor of a ‘virtual’ running programs written in the Java programming language of Pilsener. Specifically, run the code from the compiled source code, known as bytecode. The ‘processor’ is the Java Virtual Machine or JVM (Java Virtual Machine), which is responsible for translating (interpreted or compiled on the fly) the bytecode into native instructions for the platform. This allows a Java application can be executed in a variety of systems with different architectures, provided that proper implementation of the JVM. This is what has led to the famous phrase: ‘write once, run anywhere’ (write once, run anywhere). The condition is not used or so-called native functions of a platform and still not be completely assured that one true platform independence.
Since JRE version 1.2, implementation of the virtual machine from Sun includes a JIT compiler (Just In Time). In this way, instead of the traditional interpretation of the code bytecode, resulting in a slower execution of applications, the JIT converts the bytecode to native code of the destination platform. This second compilation of the code in time for punishment, but the resulting native code is executed in a more efficient and faster than if it were interpreted. Other techniques for dynamic compilation of the code during runtime allows optimizing the code even more, leaving behind on the slab that fell in Java regarding its slowness in their latest versions and the JVM has been optimized to such an extent that is no longer considered slow as a platform for running applications.
However, there can be the result of the compiled Java code can be compiled with a maximum of efficiency and benefit in terms of speed of native machine code. Although compilers are becoming increasingly sophisticated, not all libraries have an associated Java code machine equivalent to exploit. For example, the library ‘reflect’, which allows developers to explore Java instructions that are only available at runtime, is poorly represented by machine code.
Java was not the first platform based on the concept of a virtual machine, but is that it has enjoyed wide dissemination. The use of virtual machines has focused primarily on the use of emulators to support the development of hardware and operating systems under construction, but the JVM was designed to be implemented completely in software, while making it portable to any kind of hardware.

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PC Hardware Buyer’s Guide: Choosing the Perfect Components by Robert Thompson and Barbara Fritchman Thompson (Paperback – Feb 3, 2005)Illustrated

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