What is the execution engine in Java?

Execution Engine — a part of the Java Virtual Machine (JVM) responsible for executing bytecode. It reads bytecode from JVM runtime memory areas and executes instructions.

The execution engine can operate in several modes:

• Interpreter: Reads and executes bytecode line by line. Slow but simple.
• Just-In-Time (JIT) Compiler: Compiles frequently used parts of bytecode into native machine code to improve performance.
  • Hot methods are compiled.
  • Uses optimization techniques.
• Adaptive Optimizer: Flexibly switches between interpretation and compilation, adapting to the program's behavior during runtime.

// Example of simple Java code
public class MyClass {
    public static void main(String[] args) {
        int a = 5;
        int b = 10;
        int sum = a + b;
        System.out.println("Sum: " + sum);
    }
}

The JVM converts this code into bytecode (MyClass.class), which is then executed by the execution engine. The interpreter will execute each bytecode instruction sequentially. The JIT compiler can compile the main method into native code if it is called frequently, speeding up its execution.