Just-In-Time Compiler

What Does Just-In-Time Compiler Mean?

A just-in-time (JIT) compiler is a compiler that compiles code during program execution, rather than ahead of time. Many traditional compilers compiled code, transitioning between code input and machine language, well before runtime. A JIT compiler is a way to compile in real time or on the fly as the program executes.


Just-in-time compilation is also known as dynamic translation.

Techopedia Explains Just-In-Time Compiler

Ahead-of-time (AOT) compilers go through all of the code before the program is ever run. This allows for the allocation of more resources to the compile process without slowing down initial program execution. JIT compilers can be slower, because they have to balance compile resources with runtime concerns. However, one of the benefits of a JIT compiler is that the on-the-fly compile can allow for dynamic changes according to the platform.

In general, JIT compilers offer a key choice for developers and engineers, the ability to only compile when the program is run, rather than splitting up compile and initial execution into two separate stages.


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Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…