Serializing Objects - Beginning Java 2 SDK - page 482

// Read the objects back from the file
System.out.println("\nReading objects from the file: ");
try {
ObjectInputStream objectIn =
new ObjectInputStream(
new BufferedInputStream (
new FileInputStream("C:/Beg Java Stuff/Polygons.bin")));
PolyLine theLine = (PolyLine)objectIn.readObject();
System.out.println(theLine); // Display the first object
theLine = (PolyLine)objectIn.readObject();
System.out.println(theLine); // Display the second object
objectIn.close(); // Close the input stream
} catch(ClassNotFoundException e) {
e.printStackTrace(System.err);
System.exit(1);
} catch(IOException e){
e.printStackTrace(System.err);
System.exit(1);
}
}
}
This produces the output:
Polyline: (1.0,1.0) (1.0,2.0) (2.0,3.0) (-3.0,5.0) (-5.0,1.0) (0.0,0.0)
Polyline: (1.0,1.0) (1.0,2.0) (2.0,3.0) (-3.0,5.0) (-5.0,1.0) (0.0,0.0)
(10.0,10.0)
Polyline: (1.0,1.0) (1.0,2.0) (2.0,3.0) (-3.0,5.0) (-5.0,1.0) (0.0,0.0)
Reading objects from the file:
Polyline: (1.0,1.0) (1.0,2.0) (2.0,3.0) (-3.0,5.0) (-5.0,1.0) (0.0,0.0)
(10.0,10.0)
Polyline: (1.0,1.0) (1.0,2.0) (2.0,3.0) (-3.0,5.0) (-5.0,1.0) (0.0,0.0)
How It Works
We create two different PolyLine objects in the same manner as in the original example and we
display them on standard output as before. We then create an ObjectOutputStream for the file,
Polygons.bin , in the C:\Beg Java Stuff directory and write each of the PolyLine objects to the
file using the writeObject() method. You should adjust the file name and directory to suit your
environment if necessary. We then call the close() method to close the output stream. We don't need
to explicitly write the LinkedList and Point objects to the stream. These are part of the PolyLine
object so they are taken care of automatically. The same goes for when we read the PolyLine objects
back. All the subsidiary objects are reconstructed automatically.
To read the file, we create an ObjectInputStream object for Polygons.bin . We then read the first
object using the readObject() method and store the reference to it in the variable theObject . We
then output the object, read , to the standard output stream. The same process is repeated for the
second PolyLine object. It couldn't be simpler really, could it?