blips.java

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//: Blips.java
// Simple use of Externalizable & a pitfall
import java.io.*;
import java.util.*;

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

class Blip2 implements Externalizable {
	Blip2() {
		System.out.println("Blip2 Constructor");
	}
	public void writeExternal(ObjectOutput out)
		throws IOException {
		System.out.println("Blip2.writeExternal");
	}
	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.out"));
			System.out.println("Saving objects:");
			o.writeObject(b1);
			o.writeObject(b2);
			o.close();
			// Now get them back:
			ObjectInputStream in =
				new ObjectInputStream(
				new FileInputStream("Blips.out"));
			System.out.println("Recovering b1:");
			b1 = (Blip1)in.readObject();
			// OOPS! Throws an exception:
			//! System.out.println("Recovering b2:");
			//! b2 = (Blip2)in.readObject();
		} catch(Exception e) {
			e.printStackTrace();
		}
	}
} ///:~