Java The Complete Reference, Seventh Edition

ObjectInput

TheObjectInputinterface extends theDataInputinterface and defines the methods shown
in Table 19-8. It supports object serialization. Note especially thereadObject( )method. This
is called to deserialize an object. All of these methods will throw anIOExceptionon error
conditions. ThereadObject( )method can also throwClassNotFoundException.

ObjectInputStream

TheObjectInputStreamclass extends theInputStreamclass and implements theObjectInput
interface.ObjectInputStreamis responsible for reading objects from a stream. A constructor of
this class is

ObjectInputStream(InputStreaminStream)

throws IOException

The argumentinStreamis the input stream from which serialized objects should be read.
Several commonly used methods in this class are shown in Table 19-9. They will
throw anIOExceptionon error conditions. ThereadObject( )method can also throw
ClassNotFoundException. There is also an inner class toObjectInputStreamcalledGetField.
It facilitates the reading of persistent fields, and its use is beyond the scope of this book.

A Serialization Example

The following program illustrates how to use object serialization and deserialization. It begins
by instantiating an object of classMyClass. This object has three instance variables that are of
typesString,int, anddouble. This is the information we want to save and restore.

Chapter 19: Input/Output: Exploring java.io 595

Method Description

int available( ) Returns the number of bytes that are now available in the

input buffer.

void close( ) Closes the invoking stream. Further read attempts will

generate anIOException.

int read( ) Returns an integer representation of the next available byte

of input. –1 is returned when the end of the file is

encountered.

int read(bytebuffer[ ]) Attempts to read up tobuffer.lengthbytes intobuffer,

returning the number of bytes that were successfully read.

–1 is returned when the end of the file is encountered.

int read(bytebuffer[ ], intoffset,

intnumBytes)

Attempts to read up tonumBytesbytes intobufferstarting

atbuffer[offset], returning the number of bytes that were

successfully read. –1 is returned when the end of the file is

encountered.

Object readObject( ) Reads an object from the invoking stream.

long skip(longnumBytes) Ignores (that is, skips)numBytesbytes in the invoking

stream, returning the number of bytes actually ignored.

TABLE 19-8 The Methods Defined byObjectInput