Java - Returning a value from function !

Question

How does returning a value from a function internally works ?

See this example..

Answer 1

The JVM uses a value stack to hold values, and the stack is shared across all method calls on that thread. Normally, when a non-void method returns, the return value is pushed on the stack, and the caller pops it off the stack and either uses it or discards it.

Answer 2

JLS 14.17 The return Statement

[...] A return statement with no Expression attempts to transfer control to the invoker of the method or constructor that contains it.

[...] A return statement with an Expression attempts to transfer control to the invoker of the method that contains it; the value of the Expression becomes the value of the method invocation.

[...] It can be seen, then, that a return statement always completes abruptly.

The abrupt completion does mean that any following statements will not be executed, and this can in fact lead to compile-time error in some cases (JLS 14.21 Unreachable Statements)

void unreachable() {
   return;
   System.out.println("Bye!"); // DOESN'T COMPILE! Unreachable code!
}

Continuing on...

The preceding descriptions say "attempts to transfer control" rather than just "transfers control" because if there are any try statements [...] then any finally clauses [...] will be executed [...] Abrupt completion of a finally clause can disrupt the transfer of control initiated by a return statement.

This means that the following function will return -1 instead of 0.

int tryReturn() {
   try {
      return 0;
   } finally {
      return -1;
   }
}

In the absence of try-finally, though, the control will be immediately transferred, and the Expression value, if any, will be passed on to the caller.