finalize methods of different objects.
Furthermore, there are no guarantees regarding the timing of finalization.
The finalize method might be called on a finalizable object
only after an indefinite delay, if at all.
Classes whose instances hold non-heap resources should provide a method
to enable explicit release of those resources, and they should also
implement AutoCloseable if appropriate.
The java.lang.ref.Cleaner and java.lang.ref.PhantomReference
provide more flexible and efficient ways to release resources when an object
becomes unreachable.
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
A subclass overrides the finalize method to dispose of
system resources or to perform other cleanup.
The general contract of finalize is that it is invoked
if and when the Java™ virtual
machine has determined that there is no longer any
means by which this object can be accessed by any thread that has
not yet died, except as a result of an action taken by the
finalization of some other object or class which is ready to be
finalized. The finalize method may take any action, including
making this object available again to other threads; the usual purpose
of finalize, however, is to perform cleanup actions before
the object is irrevocably discarded. For example, the finalize method
for an object that represents an input/output connection might perform
explicit I/O transactions to break the connection before the object is
permanently discarded.
The finalize method of class Object performs no
special action; it simply returns normally. Subclasses of
Object may override this definition.
The Java programming language does not guarantee which thread will
invoke the finalize method for any given object. It is
guaranteed, however, that the thread that invokes finalize will not
be holding any user-visible synchronization locks when finalize is
invoked. If an uncaught exception is thrown by the finalize method,
the exception is ignored and finalization of that object terminates.
After the finalize method has been invoked for an object, no
further action is taken until the Java virtual machine has again
determined that there is no longer any means by which this object can
be accessed by any thread that has not yet died, including possible
actions by other objects or classes which are ready to be finalized,
at which point the object may be discarded.
The finalize method is never invoked more than once by a Java
virtual machine for any given object.
Any exception thrown by the finalize method causes
the finalization of this object to be halted, but is otherwise
ignored.
Throwable | the Exception raised by this method |
java.lang.ref.WeakReference, java.lang.ref.PhantomReference
@apiNote
Classes that embed non-heap resources have many options
for cleanup of those resources. The class must ensure that the
lifetime of each instance is longer than that of any resource it embeds.
java.lang.ref.Reference.reachabilityFence can be used to ensure that
objects remain reachable while resources embedded in the object are in use.
A subclass should avoid overriding the finalize method
unless the subclass embeds non-heap resources that must be cleaned up
before the instance is collected.
Finalizer invocations are not automatically chained, unlike constructors.
If a subclass overrides finalize it must invoke the superclass
finalizer explicitly.
To guard against exceptions prematurely terminating the finalize chain,
the subclass should use a try-finally block to ensure
super.finalize() is always invoked. For example,
@Override
protected void finalize() throws Throwable {
try {
... // cleanup subclass state
finally {
super.finalize();
}
}
}Diagram: Object