// Lang_30 [abstract methods].nova


// The application class.
class AbstractMethodsApp
{
   // Application class's "main" function.
   public static void main( String[] args )
   {
      // Create a new object using a concrete class and assign to an absract base class reference.
      AbstractClass abstractClassRef = new ConcreteClass( );

      // Call an instance method using the abstract class reference.
      // NOTE: Because the method is not virtual, the abstract class's method will be called.
      abstractClassRef.method0( );

      // Call a virtual method using the abstract class reference.
      // NOTE: Because the method is virtual, the concrete class's method will be called.
      abstractClassRef.method1( );

      // It is not possible to instantiate a new object using an abstract class.
      // Uncomment this line to enable the error.
//      AbstractClass abstractClass = new AbstractClass( );
   }
}


// Base abstract class.
class AbstractClass
{
   // Declare an instance method (not virtual).
   public void method0( )
   {
      Stream.writeLine( "AbstractClass.method0( ) - called" );
   }

   // Declare an abstract method.
   public abstract void method1( );
}


// Concrete class that inherits from and implements an abstract class.
class ConcreteClass : AbstractClass
{
   // Declare an instance method.
   public void method0( )
   {
      Stream.writeLine( "ConcreteClass.method0( ) - called" );
   }

   // Declare an instance method (becomes virtual via inheritance).
   public void method1( )
   {
      Stream.writeLine( "ConcreteClass.method1( ) - called" );
   }
}