EXECUTION

Implementing Finalization

12.6.1

The life cycle of an object obeys the following transition diagram, where we

abbreviate  finalizer reachable  as  f reachable :

object

A

created

reachable

reachable

reachable

J

unfinalized

finalizable

finalized

B

C

K

D

L

M

N

f reachable

f reachable

f reachable

G

E

F

unfinalized

finalizable

finalized

H

unreachable

unreachable

unfinalized

finalized

I

O

storage

finalize

 not overridden

reclaimed

When an object is first created (

A

), it is reachable and unfinalized.

As references to an object are discarded during program execution, an object

that was reachable may become finalizer reachable (

B

,

C

,

D

) or unreachable (

E

,

F

).

(Note that a finalizer reachable object never becomes unreachable directly; it

becomes reachable when the finalizer from which it can be reached is invoked, as

explained below.)

If the Java Virtual Machine detects that an unfinalized object has become

finalizer reachable or unreachable, it may label the object finalizable (

G

,

H

); more 

over, if the object was unreachable, it becomes finalizer reachable (

H

).

If the Java Virtual Machine detects that a finalized object has become

unreachable, it may reclaim the storage occupied by the object because the object

will never again become reachable (

I

).

At any time, a Java Virtual Machine may take any finalizable object, label it

finalized, and then invoke its

finalize

 method in some thread. This causes the

object to become finalized and reachable (

J

,

K

), and it also may cause other objects

that were finalizer reachable to become reachable again (

L

,

M

,

N

).

233