Explain the principle of Just-In-Time code compilation and its role in program execution.

Just-In-Time (JIT) compilation is a method of executing programs where bytecode or intermediate code is compiled into machine code directly during program execution, rather than beforehand. In Java, for example, the source code is first compiled into bytecode, which is then interpreted by the JVM. The JIT compiler analyzes frequently executed sections of code (hot spots) and compiles them into native code, significantly speeding up execution.

Role of JIT compilation:

• Improving performance by optimizing code during runtime.
• Ability to adapt optimizations to the specific execution environment.
• Combining the flexibility of interpretation with the speed of native code.

Example: In JVM, a method is initially interpreted, but upon multiple calls, the JIT compiler transforms it into machine code for faster execution.