| java.lang.Object | |
| ↳ | android.os.Parcel |
Container for a message (data and object references) that can
be sent through an IBinder. A Parcel can contain both flattened data
that will be unflattened on the other side of the IPC (using the various
methods here for writing specific types, or the general
Parcelable interface), and references to live IBinder
objects that will result in the other side receiving a proxy IBinder
connected with the original IBinder in the Parcel.
Parcel is not a general-purpose
serialization mechanism. This class (and the corresponding
Parcelable API for placing arbitrary objects into a Parcel) is
designed as a high-performance IPC transport. As such, it is not
appropriate to place any Parcel data in to persistent storage: changes
in the underlying implementation of any of the data in the Parcel can
render older data unreadable.
The bulk of the Parcel API revolves around reading and writing data of various types. There are six major classes of such functions available.
The most basic data functions are for writing and reading primitive
data types: writeByte(byte), readByte(), writeDouble(double),
readDouble(), writeFloat(float), readFloat(), writeInt(int),
readInt(), writeLong(long), readLong(),
writeString(String), readString(). Most other
data operations are built on top of these. The given data is written and
read using the endianess of the host CPU.
There are a variety of methods for reading and writing raw arrays of primitive objects, which generally result in writing a 4-byte length followed by the primitive data items. The methods for reading can either read the data into an existing array, or create and return a new array. These available types are:
Developers
writeBooleanArray(boolean[]),
readBooleanArray(boolean[]), createBooleanArray()
writeByteArray(byte[]),
writeByteArray(byte[], int, int), readByteArray(byte[]),
createByteArray()
writeCharArray(char[]), readCharArray(char[]),
createCharArray()
writeDoubleArray(double[]), readDoubleArray(double[]),
createDoubleArray()
writeFloatArray(float[]), readFloatArray(float[]),
createFloatArray()
writeIntArray(int[]), readIntArray(int[]),
createIntArray()
writeLongArray(long[]), readLongArray(long[]),
createLongArray()
writeStringArray(String[]), readStringArray(String[]),
createStringArray().
writeSparseBooleanArray(SparseBooleanArray),
readSparseBooleanArray().
The Parcelable protocol provides an extremely efficient (but
low-level) protocol for objects to write and read themselves from Parcels.
You can use the direct methods writeParcelable(Parcelable, int)
and readParcelable(ClassLoader) or
writeParcelableArray(T[], int) and
readParcelableArray(ClassLoader) to write or read. These
methods write both the class type and its data to the Parcel, allowing
that class to be reconstructed from the appropriate class loader when
later reading.
There are also some methods that provide a more efficient way to work
with Parcelables: writeTypedObject(T, int), writeTypedArray(T[], int),
writeTypedList(List, readTypedObject(Parcelable.Creator,
createTypedArray(Parcelable.Creator and createTypedArrayList(Parcelable.Creator. These methods
do not write the class information of the original object: instead, the
caller of the read function must know what type to expect and pass in the
appropriate Parcelable.Creator instead to
properly construct the new object and read its data. (To more efficient
write and read a single Parceable object that is not null, you can directly
call Parcelable.writeToParcel and
Parcelable.Creator.createFromParcel
yourself.)
A special type-safe container, called Bundle, is available
for key/value maps of heterogeneous values. This has many optimizations
for improved performance when reading and writing data, and its type-safe
API avoids difficult to debug type errors when finally marshalling the
data contents into a Parcel. The methods to use are
writeBundle(Bundle), readBundle(), and
readBundle(ClassLoader).
An unusual feature of Parcel is the ability to read and write active objects. For these objects the actual contents of the object is not written, rather a special token referencing the object is written. When reading the object back from the Parcel, you do not get a new instance of the object, but rather a handle that operates on the exact same object that was originally written. There are two forms of active objects available.
Binder objects are a core facility of Android's general cross-process
communication system. The IBinder interface describes an abstract
protocol with a Binder object. Any such interface can be written in to
a Parcel, and upon reading you will receive either the original object
implementing that interface or a special proxy implementation
that communicates calls back to the original object. The methods to use are
writeStrongBinder(IBinder),
writeStrongInterface(IInterface), readStrongBinder(),
writeBinderArray(IBinder[]), readBinderArray(IBinder[]),
createBinderArray(),
writeBinderList(List), readBinderList(List),
createBinderArrayList().
FileDescriptor objects, representing raw Linux file descriptor identifiers,
can be written and ParcelFileDescriptor objects returned to operate
on the original file descriptor. The returned file descriptor is a dup
of the original file descriptor: the object and fd is different, but
operating on the same underlying file stream, with the same position, etc.
The methods to use are writeFileDescriptor(FileDescriptor),
readFileDescriptor().
A final class of methods are for writing and reading standard Java
containers of arbitrary types. These all revolve around the
writeValue(Object) and readValue(ClassLoader) methods
which define the types of objects allowed. The container methods are
writeArray(Object[]), readArray(ClassLoader),
writeList(List), readList(List, ClassLoader),
readArrayList(ClassLoader),
writeMap(Map), readMap(Map, ClassLoader),
writeSparseArray(SparseArray),
readSparseArray(ClassLoader).
| Fields | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| STRING_CREATOR | |||||||||||
| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Read and return a new ArrayList containing IBinder objects from
the parcel that was written with
writeBinderList(List at the
current dataPosition().
| |||||||||||
Read and return a byte[] object from the parcel.
| |||||||||||
Read and return a new ArrayList containing String objects from
the parcel that was written with
writeStringList(List at the
current dataPosition().
| |||||||||||
Read and return a new array containing a particular object type from
the parcel at the current dataPosition().
| |||||||||||
Read and return a new ArrayList containing a particular object type from
the parcel that was written with
writeTypedList(List at the
current dataPosition().
| |||||||||||
Returns the amount of data remaining to be read from the
parcel.
| |||||||||||
Returns the total amount of space in the parcel.
| |||||||||||
Returns the current position in the parcel data.
| |||||||||||
Returns the total amount of data contained in the parcel.
| |||||||||||
Report whether the parcel contains any marshalled file descriptors.
| |||||||||||
Returns the raw bytes of the parcel.
| |||||||||||
Retrieve a new Parcel object from the pool.
| |||||||||||
Read and return a new Object array from the parcel at the current
dataPosition().
| |||||||||||
Read and return a new ArrayList object from the parcel at the current
dataPosition().
| |||||||||||
Read into the given List items IBinder objects that were written with
writeBinderList(List at the current dataPosition().
| |||||||||||
Read and return a new Bundle object from the parcel at the current
dataPosition(), using the given class loader to initialize the class
loader of the Bundle for later retrieval of Parcelable objects.
| |||||||||||
Read and return a new Bundle object from the parcel at the current
dataPosition().
| |||||||||||
Read a byte value from the parcel at the current dataPosition().
| |||||||||||
Read a byte[] object from the parcel and copy it into the
given byte array.
| |||||||||||
Read a double precision floating point value from the parcel at the
current dataPosition().
| |||||||||||
Throw an exception with the given message.
| |||||||||||
Special function for reading an exception result from the header of
a parcel, to be used after receiving the result of a transaction.
| |||||||||||
Read a FileDescriptor from the parcel at the current dataPosition().
| |||||||||||
Read a floating point value from the parcel at the current
dataPosition().
| |||||||||||
Please use
readBundle(ClassLoader) instead (whose data must have
been written with writeBundle(Bundle).
| |||||||||||
Read an integer value from the parcel at the current dataPosition().
| |||||||||||
Read into an existing List object from the parcel at the current
dataPosition(), using the given class loader to load any enclosed
Parcelables.
| |||||||||||
Read a long integer value from the parcel at the current dataPosition().
| |||||||||||
Please use
readBundle(ClassLoader) instead (whose data must have
been written with writeBundle(Bundle).
| |||||||||||
Read and return a new Parcelable from the parcel.
| |||||||||||
Read and return a new Parcelable array from the parcel.
| |||||||||||
Read and return a new Bundle object from the parcel at the current
dataPosition(), using the given class loader to initialize the class
loader of the Bundle for later retrieval of Parcelable objects.
| |||||||||||
Read and return a new Bundle object from the parcel at the current
dataPosition().
| |||||||||||
Read and return a new Serializable object from the parcel.
| |||||||||||
Read a Size from the parcel at the current dataPosition().
| |||||||||||
Read a SizeF from the parcel at the current dataPosition().
| |||||||||||
Read and return a new SparseArray object from the parcel at the current
dataPosition().
| |||||||||||
Read and return a new SparseBooleanArray object from the parcel at the current
dataPosition().
| |||||||||||
Read a string value from the parcel at the current dataPosition().
| |||||||||||
Read into the given List items String objects that were written with
writeStringList(List at the current dataPosition().
| |||||||||||
Read an object from the parcel at the current dataPosition().
| |||||||||||
Read into the given List items containing a particular object type
that were written with
writeTypedList(List at the
current dataPosition().
| |||||||||||
Read and return a typed Parcelable object from a parcel.
| |||||||||||
Read a typed object from a parcel.
| |||||||||||
Put a Parcel object back into the pool.
| |||||||||||
Change the capacity (current available space) of the parcel.
| |||||||||||
Move the current read/write position in the parcel.
| |||||||||||
Change the amount of data in the parcel.
| |||||||||||
Set the bytes in data to be the raw bytes of this Parcel.
| |||||||||||
Flatten an Object array into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Flatten a List containing IBinder objects into the parcel, at
the current dataPosition() and growing dataCapacity() if needed.
| |||||||||||
Flatten a Bundle into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Write a byte value into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Write a byte array into the parcel at the current
dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Write a byte array into the parcel at the current
dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Write a double precision floating point value into the parcel at the
current dataPosition(), growing dataCapacity() if needed.
| |||||||||||
Special function for writing an exception result at the header of
a parcel, to be used when returning an exception from a transaction.
| |||||||||||
Write a FileDescriptor into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Write a floating point value into the parcel at the current
dataPosition(), growing dataCapacity() if needed.
| |||||||||||
Write an integer value into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Store or read an IBinder interface token in the parcel at the current
dataPosition().
| |||||||||||
Flatten a List into the parcel at the current dataPosition(), growing
dataCapacity() if needed.
| |||||||||||
Write a long integer value into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Please use
writeBundle(Bundle) instead.
| |||||||||||
Special function for writing information at the front of the Parcel
indicating that no exception occurred.
| |||||||||||
Flatten the name of the class of the Parcelable and its contents
into the parcel.
| |||||||||||
Write a heterogeneous array of Parcelable objects into the Parcel.
| |||||||||||
Flatten a PersistableBundle into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Write a generic serializable object in to a Parcel.
| |||||||||||
Flatten a Size into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Flatten a SizeF into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Flatten a generic SparseArray into the parcel at the current
dataPosition(), growing dataCapacity() if needed.
| |||||||||||
Write a string value into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Flatten a List containing String objects into the parcel, at
the current dataPosition() and growing dataCapacity() if needed.
| |||||||||||
Write an object into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Write an object into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| |||||||||||
Flatten a heterogeneous array containing a particular object type into
the parcel, at
the current dataPosition() and growing dataCapacity() if needed.
| |||||||||||
Flatten a List containing a particular object type into the parcel, at
the current dataPosition() and growing dataCapacity() if needed.
| |||||||||||
Flatten the Parcelable object into the parcel.
| |||||||||||
Flatten a generic object in to a parcel.
| |||||||||||
| Protected Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Invoked when the garbage collector has detected that this instance is no longer reachable.
| |||||||||||
|
[Expand]
Inherited Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
| |||||||||||
Read and return a new ArrayList containing IBinder objects from
the parcel that was written with writeBinderList(List at the
current dataPosition(). Returns null if the
previously written list object was null.
Read and return a byte[] object from the parcel.
Read and return a new ArrayList containing String objects from
the parcel that was written with writeStringList(List at the
current dataPosition(). Returns null if the
previously written list object was null.
Read and return a new array containing a particular object type from
the parcel at the current dataPosition(). Returns null if the
previously written array was null. The array must have
previously been written via writeTypedArray(T[], int) with the same
object type.
Read and return a new ArrayList containing a particular object type from
the parcel that was written with writeTypedList(List at the
current dataPosition(). Returns null if the
previously written list object was null. The list must have
previously been written via writeTypedList(List with the same object
type.
Returns the amount of data remaining to be read from the
parcel. That is, dataSize()-dataPosition().
Returns the total amount of space in the parcel. This is always
>= dataSize(). The difference between it and dataSize() is the
amount of room left until the parcel needs to re-allocate its
data buffer.
Returns the current position in the parcel data. Never
more than dataSize().
Returns the total amount of data contained in the parcel.
Report whether the parcel contains any marshalled file descriptors.
Returns the raw bytes of the parcel.
The data you retrieve here must not be placed in any kind of persistent storage (on local disk, across a network, etc). For that, you should use standard serialization or another kind of general serialization mechanism. The Parcel marshalled representation is highly optimized for local IPC, and as such does not attempt to maintain compatibility with data created in different versions of the platform.
Read and return a new Object array from the parcel at the current dataPosition(). Returns null if the previously written array was null. The given class loader will be used to load any enclosed Parcelables.
Read and return a new ArrayList object from the parcel at the current dataPosition(). Returns null if the previously written list object was null. The given class loader will be used to load any enclosed Parcelables.
Read into the given List items IBinder objects that were written with
writeBinderList(List at the current dataPosition().
Read and return a new Bundle object from the parcel at the current dataPosition(), using the given class loader to initialize the class loader of the Bundle for later retrieval of Parcelable objects. Returns null if the previously written Bundle object was null.
Read and return a new Bundle object from the parcel at the current dataPosition(). Returns null if the previously written Bundle object was null.
Read a byte value from the parcel at the current dataPosition().
Read a byte[] object from the parcel and copy it into the given byte array.
Read a double precision floating point value from the parcel at the current dataPosition().
Throw an exception with the given message. Not intended for use outside the Parcel class.
| code | Used to determine which exception class to throw. |
|---|---|
| msg | The exception message. |
Special function for reading an exception result from the header of a parcel, to be used after receiving the result of a transaction. This will throw the exception for you if it had been written to the Parcel, otherwise return and let you read the normal result data from the Parcel.
Read a FileDescriptor from the parcel at the current dataPosition().
Read a floating point value from the parcel at the current dataPosition().
Please use readBundle(ClassLoader) instead (whose data must have
been written with writeBundle(Bundle). Read and return a new HashMap
object from the parcel at the current dataPosition(), using the given
class loader to load any enclosed Parcelables. Returns null if
the previously written map object was null.
Read an integer value from the parcel at the current dataPosition().
Read into an existing List object from the parcel at the current dataPosition(), using the given class loader to load any enclosed Parcelables. If it is null, the default class loader is used.
Read a long integer value from the parcel at the current dataPosition().
Please use readBundle(ClassLoader) instead (whose data must have
been written with writeBundle(Bundle). Read into an existing Map object
from the parcel at the current dataPosition().
Read and return a new Parcelable from the parcel. The given class loader will be used to load any enclosed Parcelables. If it is null, the default class loader will be used.
| loader | A ClassLoader from which to instantiate the Parcelable object, or null for the default class loader. |
|---|
| BadParcelableException | Throws BadParcelableException if there was an error trying to instantiate the Parcelable. |
|---|
Read and return a new Parcelable array from the parcel. The given class loader will be used to load any enclosed Parcelables.
Read and return a new Bundle object from the parcel at the current dataPosition(), using the given class loader to initialize the class loader of the Bundle for later retrieval of Parcelable objects. Returns null if the previously written Bundle object was null.
Read and return a new Bundle object from the parcel at the current dataPosition(). Returns null if the previously written Bundle object was null.
Read and return a new Serializable object from the parcel.
Read a Size from the parcel at the current dataPosition().
Read a SizeF from the parcel at the current dataPosition().
Read and return a new SparseArray object from the parcel at the current dataPosition(). Returns null if the previously written list object was null. The given class loader will be used to load any enclosed Parcelables.
Read and return a new SparseBooleanArray object from the parcel at the current dataPosition(). Returns null if the previously written list object was null.
Read a string value from the parcel at the current dataPosition().
Read into the given List items String objects that were written with
writeStringList(List at the current dataPosition().
Read an object from the parcel at the current dataPosition().
Read into the given List items containing a particular object type
that were written with writeTypedList(List at the
current dataPosition(). The list must have
previously been written via writeTypedList(List with the same object
type.
Read and return a typed Parcelable object from a parcel.
Returns null if the previous written object was null.
The object must have previous been written via
writeTypedObject(T, int) with the same object type.
Read a typed object from a parcel. The given class loader will be used to load any enclosed Parcelables. If it is null, the default class loader will be used.
Put a Parcel object back into the pool. You must not touch the object after this call.
Change the capacity (current available space) of the parcel.
| size | The new capacity of the parcel, in bytes. Can not be
less than dataSize() -- that is, you can not drop existing data
with this method.
|
|---|
Move the current read/write position in the parcel.
| pos | New offset in the parcel; must be between 0 and
dataSize().
|
|---|
Change the amount of data in the parcel. Can be either smaller or larger than the current size. If larger than the current capacity, more memory will be allocated.
| size | The new number of bytes in the Parcel. |
|---|
Set the bytes in data to be the raw bytes of this Parcel.
Flatten an Object array into the parcel at the current dataPosition(),
growing dataCapacity() if needed. The array values are written using
writeValue(Object) and must follow the specification there.
Flatten a List containing IBinder objects into the parcel, at
the current dataPosition() and growing dataCapacity() if needed. They
can later be retrieved with createBinderArrayList() or
readBinderList(List.
| val | The list of strings to be written. |
|---|
Flatten a Bundle into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Write a byte value into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Write a byte array into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| b | Bytes to place into the parcel. |
|---|---|
| offset | Index of first byte to be written. |
| len | Number of bytes to write. |
Write a byte array into the parcel at the current dataPosition(),
growing dataCapacity() if needed.
| b | Bytes to place into the parcel. |
|---|
Write a double precision floating point value into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Special function for writing an exception result at the header of a parcel, to be used when returning an exception from a transaction. Note that this currently only supports a few exception types; any other exception will be re-thrown by this function as a RuntimeException (to be caught by the system's last-resort exception handling when dispatching a transaction).
The supported exception types are:
| e | The Exception to be written. |
|---|
Write a FileDescriptor into the parcel at the current dataPosition(), growing dataCapacity() if needed.
The file descriptor will not be closed, which may
result in file descriptor leaks when objects are returned from Binder
calls. Use writeToParcel(Parcel, int) instead, which
accepts contextual flags and will close the original file descriptor
if PARCELABLE_WRITE_RETURN_VALUE is set.
Write a floating point value into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Write an integer value into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Store or read an IBinder interface token in the parcel at the current
dataPosition(). This is used to validate that the marshalled
transaction is intended for the target interface.
Flatten a List into the parcel at the current dataPosition(), growing
dataCapacity() if needed. The List values are written using
writeValue(Object) and must follow the specification there.
Write a long integer value into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Please use writeBundle(Bundle) instead. Flattens a Map into the parcel
at the current dataPosition(),
growing dataCapacity() if needed. The Map keys must be String objects.
The Map values are written using writeValue(Object) and must follow
the specification there.
It is strongly recommended to use writeBundle(Bundle) instead of
this method, since the Bundle class provides a type-safe API that
allows you to avoid mysterious type errors at the point of marshalling.
Special function for writing information at the front of the Parcel indicating that no exception occurred.
Flatten the name of the class of the Parcelable and its contents into the parcel.
| p | The Parcelable object to be written. |
|---|---|
| parcelableFlags | Contextual flags as per
Parcelable.writeToParcel().
|
Write a heterogeneous array of Parcelable objects into the Parcel.
Each object in the array is written along with its class name, so
that the correct class can later be instantiated. As a result, this
has significantly more overhead than writeTypedArray(T[], int), but will
correctly handle an array containing more than one type of object.
| value | The array of objects to be written. |
|---|---|
| parcelableFlags | Contextual flags as per
Parcelable.writeToParcel(). |
Flatten a PersistableBundle into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Write a generic serializable object in to a Parcel. It is strongly recommended that this method be avoided, since the serialization overhead is extremely large, and this approach will be much slower than using the other approaches to writing data in to a Parcel.
Flatten a Size into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Flatten a SizeF into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Flatten a generic SparseArray into the parcel at the current
dataPosition(), growing dataCapacity() if needed. The SparseArray
values are written using writeValue(Object) and must follow the
specification there.
Write a string value into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Flatten a List containing String objects into the parcel, at
the current dataPosition() and growing dataCapacity() if needed. They
can later be retrieved with createStringArrayList() or
readStringList(List.
| val | The list of strings to be written. |
|---|
Write an object into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Write an object into the parcel at the current dataPosition(), growing dataCapacity() if needed.
Flatten a heterogeneous array containing a particular object type into
the parcel, at
the current dataPosition() and growing dataCapacity() if needed. The
type of the objects in the array must be one that implements Parcelable.
Unlike the writeParcelableArray(T[], int) method, however, only the
raw data of the objects is written and not their type, so you must use
readTypedArray(T[], Parcelable.Creator with the correct corresponding
Parcelable.Creator implementation to unmarshall them.
| val | The array of objects to be written. |
|---|---|
| parcelableFlags | Contextual flags as per
Parcelable.writeToParcel(). |
Flatten a List containing a particular object type into the parcel, at the current dataPosition() and growing dataCapacity() if needed. The type of the objects in the list must be one that implements Parcelable. Unlike the generic writeList() method, however, only the raw data of the objects is written and not their type, so you must use the corresponding readTypedList() to unmarshall them.
| val | The list of objects to be written. |
|---|
Flatten the Parcelable object into the parcel.
| val | The Parcelable object to be written. |
|---|---|
| parcelableFlags | Contextual flags as per
Parcelable.writeToParcel(). |
Flatten a generic object in to a parcel. The given Object value may currently be one of the following types:
Bundle
writeMap(Map)).
Parcelable protocol.
writeToParcel(CharSequence, Parcel, int)).
writeList(List)).
SparseArray (as supported by writeSparseArray(SparseArray)).
IBinder
writeSerializable(Serializable) for caveats). Note that all of the
previous types have relatively efficient implementations for
writing to a Parcel; having to rely on the generic serialization
approach is much less efficient and should be avoided whenever
possible.
Parcelable objects are written with
writeToParcel(Parcel, int) using contextual flags of 0. When
serializing objects containing ParcelFileDescriptors,
this may result in file descriptor leaks when they are returned from
Binder calls (where PARCELABLE_WRITE_RETURN_VALUE
should be used).
Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.
Note that objects that override finalize are significantly more expensive than
objects that don't. Finalizers may be run a long time after the object is no longer
reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup.
Note also that finalizers are run on a single VM-wide finalizer thread,
so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary
for a class that has a native peer and needs to call a native method to destroy that peer.
Even then, it's better to provide an explicit close method (and implement
Closeable), and insist that callers manually dispose of instances. This
works well for something like files, but less well for something like a BigInteger
where typical calling code would have to deal with lots of temporaries. Unfortunately,
code that creates lots of temporaries is the worst kind of code from the point of view of
the single finalizer thread.
If you must use finalizers, consider at least providing your own
ReferenceQueue and having your own thread process that queue.
Unlike constructors, finalizers are not automatically chained. You are responsible for
calling super.finalize() yourself.
Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.
| Throwable |
|---|