The following code throws a "ClassNotFoundException: int"  exception:

import java.io.*;
public class Primtest extends Object {

  /** Creates new Primtest */
  public Primtest() {
  }
  
  /**
  * @param args the command line arguments
  */
  public static void main (String args[]) {
      try {
        ByteArrayOutputStream o = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(o);
        Class c = int.class;
        oos.writeObject(c);
        oos.close();
        o.close();
        ByteArrayInputStream i = new ByteArrayInputStream(o.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(i);
        c = (Class)ois.readObject();
      } catch (Exception e){
        e.printStackTrace();
      }
  }

}