Cleaner

public final class Cleaner
extends Object

java.lang.Object
   ↳ java.lang.ref.Cleaner

Cleaner manages a set of object references and corresponding cleaning actions.

Cleaning actions are registered to run after the cleaner is notified that the object has become phantom reachable. The cleaner uses PhantomReference and ReferenceQueue to be notified when the reachability changes.

Each cleaner operates independently, managing the pending cleaning actions and handling threading and termination when the cleaner is no longer in use. Registering an object reference and corresponding cleaning action returns a Cleanable. The most efficient use is to explicitly invoke the clean method when the object is closed or no longer needed. The cleaning action is a Runnable to be invoked at most once when the object has become phantom reachable unless it has already been explicitly cleaned. Note that the cleaning action must not refer to the object being registered. If so, the object will not become phantom reachable and the cleaning action will not be invoked automatically.

The execution of the cleaning action is performed by a thread associated with the cleaner. The thread runs until all registered cleaning actions have completed and the cleaner itself is reclaimed by the garbage collector.

The behavior of cleaners during System.exit is implementation specific. No guarantees are made relating to whether cleaning actions are invoked or not.

Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

Summary

Nested classes

interface Cleaner.Cleanable

Cleanable represents an object and a cleaning action registered in a Cleaner. 

Public methods

static Cleaner create(ThreadFactory threadFactory)

Returns a new Cleaner using a Thread from the ThreadFactory.

static Cleaner create()

Returns a new Cleaner.

Cleaner.Cleanable register(Object obj, Runnable action)

Registers an object and a cleaning action to run when the object becomes phantom reachable.

Inherited methods

Public methods

create

Added in API level 33 
public static Cleaner create (ThreadFactory threadFactory)

Returns a new Cleaner using a Thread from the ThreadFactory.

A thread from the thread factory's newThread method is set to be a daemon thread and started to process phantom reachable objects and invoke cleaning actions. On each call the thread factory must provide a Thread that is suitable for performing the cleaning actions.

The cleaner terminates when it is phantom reachable and all of the registered cleaning actions are complete.

Parameters
threadFactory ThreadFactory: a ThreadFactory to return a new Thread to process cleaning actions
Returns
Cleaner a new Cleaner
Throws
IllegalThreadStateException if the thread from the thread factory was not a new thread.
SecurityException if the current thread is not allowed to create or start the thread.

create

Added in API level 33 
public static Cleaner create ()

Returns a new Cleaner.

The cleaner creates a daemon thread to process the phantom reachable objects and to invoke cleaning actions. The context class loader of the thread is set to the system class loader. The thread has no permissions, enforced only if a SecurityManager is set.

All exceptions thrown by the cleaning actions in this thread are ignored.

The cleaner terminates when it is phantom reachable and all of the registered cleaning actions are complete.

Returns
Cleaner a new Cleaner
Throws
SecurityException if the current thread is not allowed to create or start the thread.

register

Added in API level 33 
public Cleaner.Cleanable register (Object obj, 
                Runnable action)

Registers an object and a cleaning action to run when the object becomes phantom reachable. Refer to the API Note above for cautions about the behavior of cleaning actions.

Parameters
obj Object: the object to monitor
action Runnable: a Runnable to invoke when the object becomes phantom reachable
Returns
Cleaner.Cleanable a Cleanable instance