java.io
Interface Externalizable
- Serializable
- RemoteRef, ServerRef
- DataFlavor
This interface provides a way that classes can completely control how
the data of their object instances are written and read to and from
streams. It has two methods which are used to write the data to a stream
and to read the data from a stream. The read method must read the data
in exactly the way it was written by the write method.
Note that classes which implement this interface must take into account
that all superclass data must also be written to the stream as well.
The class implementing this interface must figure out how to make that
happen.
This interface can be used to provide object persistence. When an
object is to be stored externally, the
writeExternal method is
called to save state. When the object is restored, an instance is
created using the default no-argument constructor and the
readExternal method is used to restore the state.
void | readExternal(ObjectInput in)- This method restores an object's state by reading in the instance data
for the object from the passed in stream.
|
void | writeExternal(ObjectOutput out)- This method is responsible for writing the instance data of an object
to the passed in stream.
|
readExternal
public void readExternal(ObjectInput in)
throws ClassNotFoundException,
IOException This method restores an object's state by reading in the instance data
for the object from the passed in stream. Note that this stream is not
a subclass of
InputStream, but rather is a class that
implements
the
ObjectInput interface. That interface provides a
mechanism for
reading in Java data types from a stream.
Note that this method must be compatible with
writeExternal.
It must read back the exact same types that were written by that
method in the exact order they were written.
If this method needs to read back an object instance, then the class
for that object must be found and loaded. If that operation fails,
then this method throws a
ClassNotFoundException
in - An ObjectInput instance for reading in the object
state
writeExternal
public void writeExternal(ObjectOutput out)
throws IOException This method is responsible for writing the instance data of an object
to the passed in stream. Note that this stream is not a subclass of
OutputStream, but rather is a class that implements the
ObjectOutput interface. That interface provides a
number of methods
for writing Java data values to a stream.
Not that the implementation of this method must be coordinated with
the implementation of
readExternal.
out - An ObjectOutput instance for writing the
object state
Externalizable.java -- Interface for saving and restoring object data
Copyright (C) 1998 Free Software Foundation, Inc.
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