What is an Execution Engine in the context of Java?

The Execution Engine in the JVM is responsible for executing bytecode. It consists of three main components:

1. Interpreter: Reads and executes bytecode line by line. Simple but slow for frequently executed parts of the code.
2. JIT Compiler (Just-In-Time): Compiles frequently repeated parts of bytecode (hot spots) into machine code for faster execution. Uses profiling to identify such sections. It consists of:
   • Optimizer: Performs code optimizations.
   • Code Generator: Generates machine code.
   • Deoptimizer: Reverts optimizations if necessary (for example, from 32-bit to 64-bit representation).
3. Garbage Collector: Automatically manages memory by freeing objects that are no longer referenced. Works in the background.