Java IO.pdf - Nguyen Dang Binh

Java I/O
To write an object onto a stream, you chain an object output stream to the stream, then pass
the object to the object output stream's writeObject() method:
public final void writeObject(Object o) throws IOException
For example:
try {
Point p = new Point(34, 22);
FileOutputStream fout = new FileOutputStream("point.ser");
ObjectOutputStream oout = new ObjectOutputStream(fout);
oout.writeObject(p);
oout.close();
}
catch (Exception e) {System.err.println(e);}
Later, the object can be read back using the readObject() method of the
ObjectInputStream class:
public final Object readObject()
throws OptionalDataException, ClassNotFoundException,
IOException
For example:
try {
FileInputStream fin = new FileInputStream("point.ser");
ObjectInputStream oin = new ObjectInputStream(fin);
Object o = oin.readObject();
Point p = (Point) o;
oin.close();
}
catch (Exception e) {System.err.println(e);}
The reconstituted point has the same values as the original point. Its x is 34 and its y is 22, just
like the Point object that was written. However, since readObject() is only declared to
return an Object, you usually need to cast the deserialized object to a more specific type.
Both writeObject() and readObject() throw IOException for all the usual reasons an I/O
operation can fail (disk filling up, network connection being severed, etc.). The
readObject() method also throws OptionalDataException if the stream doesn't appear to
contain an object in the proper format or a ClassNotFoundException if a definition for the
class of the object read from the input stream is not available in the current VM.
11.3 How Object Serialization Works
Objects possess state. This state is stored in the values of the nonstatic, nontransient fields of
an object's class. Consider this TwoDPoint class:
public class TwoDPoint {
public double x;
public double y;
}
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