// serialization/Blips.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Simple use of Externalizable & a pitfall
import java.io.*;

class Blip1 implements Externalizable {
 public Blip1() {
 System.out.println("Blip1 Constructor");
 }
 @Override
 public void writeExternal(ObjectOutput out)
 throws IOException {
 System.out.println("Blip1.writeExternal");
 }
 @Override
 public void readExternal(ObjectInput in)
 throws IOException, ClassNotFoundException {
 System.out.println("Blip1.readExternal");
 }
}

class Blip2 implements Externalizable {
 Blip2() {
 System.out.println("Blip2 Constructor");
 }
 @Override
 public void writeExternal(ObjectOutput out)
 throws IOException {
 System.out.println("Blip2.writeExternal");
 }
 @Override
 public void readExternal(ObjectInput in)
 throws IOException, ClassNotFoundException {
 System.out.println("Blip2.readExternal");
 }
}

public class Blips {
 public static void main(String[] args) {
 System.out.println("Constructing objects:");
 Blip1 b1 = new Blip1();
 Blip2 b2 = new Blip2();
 try(
 ObjectOutputStream o = new ObjectOutputStream(
 new FileOutputStream("Blips.serialized"))
 ) {
 System.out.println("Saving objects:");
 o.writeObject(b1);
 o.writeObject(b2);
 } catch(IOException e) {
 throw new RuntimeException(e);
 }
 // Now get them back:
 System.out.println("Recovering b1:");
 try(
 ObjectInputStream in = new ObjectInputStream(
 new FileInputStream("Blips.serialized"))
 ) {
 b1 = (Blip1)in.readObject();
 } catch(IOException | ClassNotFoundException e) {
 throw new RuntimeException(e);
 }
 // OOPS! Throws an exception:
 //- System.out.println("Recovering b2:");
 //- b2 = (Blip2)in.readObject();
 }
}
/* Output:
Constructing objects:
Blip1 Constructor
Blip2 Constructor
Saving objects:
Blip1.writeExternal
Blip2.writeExternal
Recovering b1:
Blip1 Constructor
Blip1.readExternal
*/