What is JIT compiler in java

What is JIT compiler in java?

The JIT compiler, short for Just-In-Time compiler, is a key component of the Java Virtual Machine (JVM). It plays a crucial role in optimizing the performance of Java applications. Here’s how it works:

Java Compilation Process:

  1. Java Source Code: Java programs are initially written in human-readable form as source code files (with a .java extension).
  2. Compilation: The Java compiler (javac) compiles the source code into bytecode. Bytecode is an intermediate, platform-independent representation of the program (files with a .class extension). These bytecode files can be executed on any system with a compatible JVM.

Execution Process with JIT Compilation:

  1. Loading Bytecode: When a Java program is run, the JVM loads the bytecode files.
  2. Interpretation: Initially, the JVM interprets the bytecode line by line. Interpretation is straightforward but can be slow because it involves translating each bytecode instruction into native machine code as the program runs.
  3. Profiling: While interpreting the bytecode, the JVM collects data about which parts of the program are executed frequently (hotspots).
  4. Compilation: When the JVM detects that a particular section of the bytecode is executed frequently (a hotspot), it uses the JIT compiler to compile that section of bytecode into native machine code specific to the host system. This compilation happens on-the-fly, just before the code is executed. Only the hotspots are compiled, not the entire program.
  5. Execution of Native Code: The compiled native code is then executed directly by the CPU. Compiled native code runs much faster than interpreted bytecode because it’s in the format that the CPU understands directly.

Benefits of JIT Compilation:

  • Performance: By compiling hotspots into native code, the program’s performance is significantly improved. Compiled native code executes much faster than interpreted bytecode.
  • Adaptability: The JIT compiler adapts to the runtime behavior of the program. Hotspots change as the program runs, and the JIT compiler can recompile different parts of the code as needed.
  • Optimization: The JIT compiler can apply various optimization techniques to the compiled code, tailoring the optimizations to the specific characteristics of the executed code.

In summary, the JIT compiler in Java enhances performance by compiling frequently executed parts of the bytecode into native machine code. This on-the-fly compilation significantly speeds up the execution of Java applications.

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