// file:    Version4.java
// author:  keller
// purpose: demonstrating use of abstract methods
//
// description:
// There is a base class and two derived classes.  
// Each overloads a method 'op'.
//
// In this version, virtual is not used at all.  Consequently, the version
// of op that gets called is determined strictly by the parameter type 
// (based or derived) through which the object is referred.

abstract class Base
{
abstract String op();
};


class Derived_1 extends Base
{
String op()
  {
  return "op() of Derived_1";
  }
};


class Derived_2 extends Base
{
String op()
  {
  return "op() of Derived_2";
  }
};


class Version4
{
static void testAsBase(Base object)
  {
  System.out.println("testAsBase: " + object.op());
  }

static void testAsDerived_1(Derived_1 object)
  {
  System.out.println("testAsDerived_1: " + object.op());
  }

static void testAsDerived_2(Derived_2 object)
  {
  System.out.println("testAsDerived_2: " + object.op());
  }


public static void main(String arg[])
  {
  Derived_1 ob_1 = new Derived_1();
  Derived_2 ob_2 = new Derived_2();

  testAsBase(ob_1);
  testAsBase(ob_2);

  testAsDerived_1(ob_1);
  testAsDerived_2(ob_2);
  }
}

/* output of Version 1:

testAsBase: op() of Base
testAsBase: op() of Derived_1
testAsBase: op() of Derived_2
testAsDerived_1: op() of Derived_1
testAsDerived_2: op() of Derived_2

*/