What happens at compile time?

At compile time, java file is compiled by Java Compiler (It does not interact with OS) and converts the java code into bytecode.

[Complier]

What happens at runtime?

At runtime, following steps are performed:

[phases]

Classloader:

is the subsystem of JVM that is used to load class files.

Bytecode Verifier:

checks the code fragments for illegal code that can violate access right to objects.

Interpreter:

read bytecode stream then execute the instructions. -