just in-time compilation

JITcompilation(Just In-Time Compilation) is a technique used by interpreters and runtime environments such as the Java Virtual Machine( JVM) and the .Net runtime system to execute programs. Unlike compilers that convert the entire source code into an executable program in one pass, the JIT compiler operates mainly during program execution. It then compiles only those parts of the program that are actually to be executed.

This has the following advantages:

• Only a very small part is compiled before the program is started. The delays with the program start known from the first JVM versions are void thereby.
• Program parts, which are never run, are also not compiled. This saves system resources.
• Once as a finished compiled program parts are held by the JVM a software cache and do not have to be recompiled with a further run.

In contrast to the classical compilation, with which the program is present completely compiled, JIT compilation remains nevertheless behind in the execution time.