What happens to the stack when exiting a method?

Question

I was reading What and where are the stack and heap?. One thing I am a bit fuzzy on is what happens to the stack after a method exits. Take this image for example:

The stack is cleared upon exiting the method, but what does that mean? Is the pointer at the stack just moved back to the start of the stack making it empty? I hope this is not too broad of a question. I am not really sure what is going on behind the scenes when the stack is cleared from exiting a method.

Answer 1

When a method is called, local variables are located on the stack. Object references are also stored on the stack, corresponding objects are store in the heap.

The stack is just a region of memory, it has a start and end address. The JVM (java virtual machine) has a register which points to the current top of the stack (stack pointer). If a new method is called, an offset will be added to the register to get new space on the stack.

When a method call is over, the stack pointer will be decreased by this offset, this frees the allocated space.

Local variables and other stuff (like return address, parameters...) may still on the stack and will be overwritten by next method call.

BTW: this is why java stored all objects in heap. When an object would be located on the stack, and you would return the reference which points to the stack, the object could be destroyed by next method call.