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Table of contents
What is JIT?
Working of JIT compiler
Work Flow of JIT
Advantages and disadvantages of JIT
Frequently Asked Questions:
Key Takeaways:
Last Updated: Mar 27, 2024

Just In Time Compiler

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When a piece of code is written in any programming language, it needs something to convert that piece of code into machine understandable form because the device only understands the binary language. The Just in Time Compiler(JIT) is an essential part of the JRE responsible for performing java-based applications at run time. The main aim of the compiler is to increase the performance of an application for the user and the developer.

Also read, Duck Number in Java and Hashcode Method in Java.

What is JIT?

Bytecode is an essential feature of Java that helps in cross-platform execution. Depending on the instruction set architecture, the bytecode must be interpreted and compiled to the proper machine instruction code. JIT in Java is an integral part of the JVM. It enhances the execution level many times over the previous level. It optimises the performance of the Java application at compile time. The primary defining characteristic of a JIT compiler is that a JIT compiler runs after a program starts and compiles code. 

The JIT compilation includes two approaches AOT  (Ahead-Of-Time compilation) and interpretation to translate code into machine language. AOT compiles the code into a native machine language. It transforms the bytecode of a Virtual Machine into machine code.

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Working of JIT compiler

After getting the bytecode, the JIT compiler transforms it into the native code. However, that bytecode may have a significant impact on the speed and performance of an application. To improve performance, the JIT compiler will, at runtime, compile suitable bytecode sequences into machine code. The code is typically sent to a processor, where the code instructions are carried out. Code that looks like it can be re-optimized is called “Hot.” With less chance of code being interpreted multiple times, there is less overhead, faster execution speeds. This is why most of the implementations of JVM use JIT compilers.

Work Flow of JIT

JDK provides a java compiler to compile the java source code into the bytecode. After that, JVM loads the .class file at runtime and transforms the bytecode into the binary code. Further, the machine code is used by the interpreter.

  • The interpretation of Java bytecode reduces the performance of the native application. It is the reason to implement the JIT compiler. The JIT compiler increases the performance of the application by compiling the bytecode into machine code,
  • It is enabled by default when a method is invoked. The JVM directly invokes the compiled code of the procedure without interpreting it. It does not require much memory usage.

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Advantages and disadvantages of JIT


  • JIT needs less memory usage:
  • JIT compilers run after a program starts.
  • Code optimization can be performed while coding execution.
  • Cade can be localised on the same page.
  • It can use different levels of optimization.


  • Startup takes up a lot of time.
  • Heavy usage of cache memory.
  • Increases the level of complexity in Java programs.

Frequently Asked Questions:

Q: What is the difference between JIT and JVM compilation?

A: The JVM directly calls the compiled code instead of interpreting it. If compiling did not require any processor time or memory usage, the speed native compiler would have been the same. JIT compilation requires processor time and memory usage.


Q: How much does the code cache consume?

A: The JIT compiler uses memory intelligently. When the code cache is initialised, it consumes relatively more minor memory. Space that was previously occupied by discarded methods is reclaimed and reused. The JIT compiler methods avoid exhausting the system memory and affecting the system memory and affecting the stability of the application or the operating system.

Key Takeaways:

In this blog, we covered the topics mentioned below:

  • What is the JIT compiler?
  • Working of JIT compiler
  • Work Flow of the JIT compiler
  • Advantages and disadvantages of the JIT compiler.

If you want to explore more about JIT, you can visit this webpage, JIT Compiler.

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