What Is Just-In-Time (JIT)?

The term "just-in-time" has been applied to a variety of concepts in software development—and sometimes, it's used to describe things that aren't Just-In-Time (JIT). The most common term is software compilation: compiling your code only when it needs to be run. This has traditionally been done by compilers that compile your code as required so as not to waste computing time or memory on collecting something that might not be used for weeks or months. Another everyday use of the term is about activating an object only when it needs to do its job. This is usually done through a garbage collector or similar mechanism that can determine when there are no more references to an object and remove it from memory. It doesn't waste resources on keeping objects around longer than necessary. In the beginning, there was only one way to convert high-level code to object code: by hand. This was slow and tedious but inevitable—until the JIT compilation came along. The concept of JIT compilation arose from the desire for a compiler to perform more than just converting a high-level language to machine code (object code). JIT compilers allow for portability across various operating systems and hardware platforms. JIT compilation is supported by languages such as Smalltalk, Pascal, Java, and C#, among others. JIT compilers are so effective because they can optimize their output based on runtime data rather than relying purely on static analysis of the source code. They also provide two key benefits: fast startup times and improved dynamic optimization. JIT compilation is great, but it suffers from a few key problems. First, the compilation process happens at runtime and can take a while to complete. This means that your application takes longer to launch and uses resources more slowly than it could if you had precompiled your code ahead of time. Instead, you can get around these issues by using ahead-of-time (AOT) compilation. AOT compiles your entire Microsoft intermediate language image into machine code before you run the program, so there's no need for runtime compilation or any slowdown during execution. Once your code is compiled, you don't have to do anything else; load it up and go!