Which way is used to allocate/deallocate memory for locals?

Question

Good afternoon.
I would like to know how memory is allocated/deallocated for local variables in an activation record/frame. For example, in the following java code:
1 public void test()
2 {
3     {          
4          {
5               String y = "abc";
6          }
7     }
8     {
9          String y = "pqr";
10     }
11 } At line 5, memory is allocated for variable y. Is this memory deallocated at line 6 (right after its declaration block), or after the line 11 at which point the whole activation record for the method is popped out of the stack?
In addition, is this local memory allocation/deallocation strategy required by the Java specification, or could be different with different Java compilers? Thank you very much and have a great weekend,
Sunny

Answer 1

Hi,
Thank you for your comments!
Perhaps I did not state my problems clearly. Here is my real purpose: I am trying to monitor a program's runtime behavior by dynamically maintaining an object graph where nodes represent runtime objects and directed edges represent "refer to" relation between objects. To better understand my questions, let me first briefly introduce my algorithm to update the object graph:
1. add an edge (between objects): when a local refers to an object, add an edge from the enclosing object to the referred object
2. delete an edge: when a local refers to another new object, delete the edge from the enclosing object to the previously referred object; or the memory allocated for this local is deallocated.
For example, if I have the following Java method,
1 m()
2 {
3        {
4                 Object x = objA;
4'                x = objB;
5                 // some statements
6        }
7        {
8                 // some statements
8'                Object x = objC;
9        }
10 }Below, the enclosing obj means the object containing the method m().
At line 4, a local name x is declared and assigned objA, at which point an edge from the enclosing obj to objA should be added. At line 4' the same local is assigned a new value, at which point we should delete the edge from the enclosing obj to objA and add a new edge to objB.
At line 6 this local is out of its scope, whether or not we should delete the edge from the enclosing obj to objB depends on whether the memory allocated for x is deallocated.
Lastly, at line 8' a new local with the same name x is declared so we should add a new edge...
Another example is like this:
1 m1()
2 {
3      Object x = objA;
4     // some statements
5     m2();
6 }
7 m2()
8 {
9     Object x = objB;
10     // some statements
11 }After line 9, I should be able to know the enclosing obj has two outgoing edges labeled with x, one is to objA and the other is to objB.
Is there any solution to getting this runtime information for Java local variables? I would really appreciate any help!
-- Sunny