// file:    Vehicle.java
// author:  Robert Keller
// purpose: Illustrating abstract classes

import java.io.*;

// The base class, Vehicle, which is abstract.

abstract class Vehicle
{
abstract String type();


public static void main(String arg[])
  {
  Vehicle a, b;
  
  a = new Automobile();		// ok, since Automobile is a kind of Vehicle
  b = new Boat();		// ok, since Boat is a kind of Vehicle

  System.out.println(a.type());
  System.out.println(b.type());

  System.out.println("a " + analysis(a));
  System.out.println("b " + analysis(b));
  }

// create a more complete analysis of this object
// Traces Object o's class up the hierarchy until the root Object is reached,
// as signified by the class having no parent (superClass)

static String analysis(Object o)
  {
  StringBuffer b = new StringBuffer();

  Class c = o.getClass();
  Class parent = c.getSuperclass();
  while( parent != null )
    {
    b.append("is a " + c.getName() + ", ");
    c = parent;
    parent = c.getSuperclass();    
    }
  b.append("is an Object.");
  return b.toString();
  }

} // Vehicle


// The class Automobile, a special case of Vehicle

class Automobile extends Vehicle
{

String type()
  {
  return "Automobile";
  }
} // Automobile


// The class Boat, a special case of Vehicle

class Boat extends Vehicle
{
String type()
  {
  return "Boat";
  }
} // Boat