class myPoint implements Serializable{ 
} 
 

void writeExternal(ObjectOutput out) throws IOException; 
void readExternal(ObjectInput in) throws IOException,ClassNotFoundException; 
public class Point implements Externalizable { 
  private int a; 
  private int b; 
  public Point(int a, int b) { 
    this.a = a; 
    this.b = b; 
  } 
  public Point() { 
  } 
  public String toString() { 
    return a + " , " + b; 
  } 
   
  public void writeExternal(ObjectOutput out) throws IOException { 
    out.write(a); 
    out.write(b); 
  } 
  public void readExternal(ObjectInput in) throws IOException, 
      ClassNotFoundException { 
    a = in.read(); 
    b = in.read(); 
  } 
  public static void main(String[] args) throws IOException, 
      ClassNotFoundException { 
    String file = "d://1.txt"; 
    Point p = new Point(1, 2); 
    System.out.println(p); 
    FileOutputStream fos = new FileOutputStream(file); 
    ObjectOutputStream oos = new ObjectOutputStream(fos); 
    oos.writeObject(p); 
    FileInputStream fis = new FileInputStream(file); 
    ObjectInputStream ois = new ObjectInputStream(fis); 
    Point pp = (Point) ois.readObject(); 
    System.out.println(pp); 
  } 
} 
 

public class StringList implements Serializable { 
  private transient int size = 0; 
  private transient Entity head = null; 
  public final void add(String str) { 
    // ... 
  } 
  private static class Entity { 
    String data; 
    Entity next; 
    Entity previous; 
  } 
  private void writeObject(ObjectOutputStream s) throws IOException { 
    s.defaultWriteObject(); 
    s.write(size); 
    for (Entity e = head; e != null; e = e.next) { 
      s.writeObject(e.data); 
    } 
  } 
  private void readObject(ObjectInputStream s) throws IOException, 
      ClassNotFoundException { 
    s.defaultReadObject(); 
    int num = s.read(); 
    for (int i = 0; i < num; i++) { 
      this.add((String) s.readObject()); 
    } 
  } 
} 
 

import java.io.InvalidObjectException; 
import java.io.ObjectInputStream; 
import java.io.Serializable; 
import java.util.Date; 
public final class Period implements Serializable { 
  private static final long serialVersionUID = 100L; 
  private final Date start; 
  private final Date end; 
  public Period(Date start, Date end) { 
    this.start = new Date(start.getTime()); 
    this.end = new Date(end.getTime()); 
    if (this.start.compareTo(this.end) > 0) { 
      throw new IllegalArgumentException(start + " after " + end); 
    } 
  } 
  public Date start() { 
    return new Date(start.getTime()); 
  } 
  public Date end() { 
    return new Date(end.getTime()); 
  } 
  public String toString() { 
    return start + " - " + end; 
  } 
  // 不给 
  private Object writeReplace() { 
    return new SerializationProxy(this); 
  } 
  private void readObject(ObjectInputStream stream) 
      throws InvalidObjectException { 
    throw new InvalidObjectException("proxy request"); 
  } 
  private static class SerializationProxy implements Serializable { 
    private final Date start; 
    private final Date end; 
    SerializationProxy(Period p) { 
      this.start = p.start; 
      this.end = p.end; 
    } 
    private Object readResolve() { 
      return new Period(start, end); 
    } 
    private static final long serialVersionUID = 1000L; 
  } 
}