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This class
holds the values of named
fields read by an
ObjectInputStream. It gives the programmer precise
control over the deserialization process and is typically used when
implementing an object with a set of fields that do not match the set
of fields (and the serialization stream format) of the original
implementation of the object. This class allows the implementation of
a class to change without breaking
serialization compatibility.In order to use the
GetField class, your class must implement a
private readObject( ) method that is responsible
for custom deserialization. Typically, when using the
GetField class, you have also specified an array
of ObjectStreamField objects as the value of a
private static field named serialPersistentFields.
This array specifies the names and types of all fields expected to be
found when reading from a serialization stream. If there is no
serialPersistentField field, the array of
ObjectStreamField objects is created from the
actual fields (excluding static and
TRansient fields) of the class.Within the readObject(
) method of your class, call the readFields(
) method of ObjectInputStream( ). This
method reads the values of all fields from the stream and stores them
in an ObjectInputStream.GetField object that it
returns. This GetField object is essentially a
mapping from field names to field values, and you can extract the
values of whatever fields you need in order to restore the proper
state of the object being deserialized. The various get(
) methods return the values of named fields of specified
types. Each method takes a default value as an argument, in case no
value for the named field was present in the serialization stream.
(This can happen when deserializing an object written by an earlier
version of the class, for example.) Use the defaulted(
) method to determine whether the
GetField object contains a value for the named
field. If this method returns true, the named
field had no value in the stream, so the get( )
method of the GetField object has to return the
specified default value. The getObjectStreamClass(
) method of a GetField object returns
the ObjectStreamClass object for the object being
deserialized. This ObjectStreamClass can obtain
the array of ObjectStreamField objects for the
class.
See also
ObjectOutputStream.PutField
public abstract static class ObjectInputStream.GetField {
// Public Constructors
public GetField ( );
// Public Instance Methods
public abstract boolean defaulted (String name ) throws IOException;
public abstract boolean get (String name , boolean val ) throws IOException;
public abstract byte get (String name , byte val ) throws IOException;
public abstract char get (String name , char val ) throws IOException;
public abstract short get (String name , short val ) throws IOException;
public abstract int get (String name , int val ) throws IOException;
public abstract long get (String name , long val ) throws IOException;
public abstract float get (String name , float val ) throws IOException;
public abstract double get (String name , double val ) throws IOException;
public abstract Object get (String name , Object val ) throws IOException;
public abstract ObjectStreamClass getObjectStreamClass ( );
}Returned By
ObjectInputStream.readFields( )
