Walk through what happens from a .java file to a running program.

You write source in a .java file. The compiler javac checks it and produces one .class file per class, containing bytecode.

You launch it with `java YourClass`; the JVM starts, its class loader loads the needed .class files, the bytecode verifier checks them for safety, and then the JVM executes your program starting at the main method -- interpreting the bytecode and, for hot code, JIT-compiling it to native machine code for speed.