// Copyright 1997, <a href=http://www.MageLang.com>MageLang Institute</a>.

import java.io.*;
import java.util.Date;
import java.util.Vector;
import java.util.Enumeration;

class TreeNode implements Serializable, ObjectInputValidation {
  Vector children;
  TreeNode parent;
  String name;
  /* the timeStamp will mark when this object is 
     instantiated or read from a stream */
  transient Date timeStamp;

  /* the magic number will keep track of how often this
     object is read in from a stream */
  transient int magicNumber = 0; 
 
  public TreeNode(String s) {
     children = new Vector(5);
     name = s;
     timeStamp = new Date();
  }

  public void addChild(TreeNode n) {
     children.addElement(n);
     n.parent = this;
  }

  private void writeObject(ObjectOutputStream stream)
          throws IOException {
     try {
       stream.defaultWriteObject();
       stream.writeInt(magicNumber);
     } catch(Exception e) { System.out.println(e); }
  }

  private void readObject(ObjectInputStream stream)
          throws IOException {
     try {
       stream.registerValidation(this,0);
       stream.defaultReadObject();
       magicNumber = stream.readInt() + 1;
       timeStamp = new Date();
     } catch(Exception e) { System.out.println(e); }

  }

  /** check that each child has this object as it's parent */
  public void validateObject() 
         throws InvalidObjectException {
     Enumeration e = children.elements();
     while(e.hasMoreElements()) {
        if(((TreeNode)e.nextElement()).parent != this)
           throw new InvalidObjectException(getClass().getName());
     }
  }

  public String toString() {
     Enumeration e = children.elements();
     StringBuffer buff = new StringBuffer(100);
     buff.append("[ " +  name + "(magicNum:" + 
                 magicNumber + ")(tStamp:" + timeStamp + ") : ");
     while(e.hasMoreElements()) {
         buff.append(e.nextElement().toString());
     }
     buff.append(" ] ");
     return buff.toString();
  }

}

public class ValidateTest {

  public static void main(String[] args) {

  // first build a tree
  TreeNode top = new TreeNode("top");
  top.addChild(new TreeNode("left"));
  top.addChild(new TreeNode("right"));

  // print it out to see how it looks
  System.out.println("source tree:  \n" + top.toString());

   // now write the tree to a file, and read it back in again
   try {
     FileOutputStream fOut = new FileOutputStream("test.out");
     ObjectOutput out = new ObjectOutputStream(fOut);
     out.writeObject(top);
     out.flush();
     out.close();

     FileInputStream fIn = new FileInputStream("test.out");
     ObjectInputStream in = new ObjectInputStream(fIn);
     TreeNode n = (TreeNode)in.readObject();
     in.close();
     System.out.println("read tree: \n" + n.toString());
   } catch (Exception e) { System.out.println("exception: " + e); }
  }

}