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Just-In-Time Compilation

Performance is one of the major problems concerning Java™. Once downloaded, Java applets deliver high performance on complex applications. However, the code is run as interpreted and not compiled, so performance will never be as good as an executable. To address this problem, some browsers support a facility called Just-in-Time compilation, commonly referred to as JIT.

When browsers supporting JIT receive a Java applet for the first time, it converts the Java byte code into a native program, which it saves to disk. The browser then executes the program. In effect, JIT uses the Java byte codes as a source language, which it then compiles into a local machine program. JIT has several advantages. Since the code is not changed in any way, the resulting program is still secure and machine independent, and download times are minimized. The real benefit is in the execution speed. JIT compiled programs execute several times faster than even the best Java byte code emulators.

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