// Lang_31 [interfaces].nova



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

      // Call a virtual method using the abstract class reference.
      a.method0( );

      // Call a virtual method using the abstract class reference.
      a.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( );
   }
}



// Declare an interface.
interface IAbstract
{
   // Declare an implicit abstract method.
   public IAbstract method0( );

   // The "abstract" keyword is optional in an interface definition.
   public abstract void method1( );
}



// Declare an interface.
interface IAbstract2 : IAbstract
{
   // Redefine "method0" with a covariant return type.
   public IAbstract2 method0( );
}



// Concrete class that implements the defined interface.
class ConcreteClass : IAbstract, IAbstract2
{
   // Declare an instance method.
   public ConcreteClass method0( )
   {
      Stream.writeLine( "ConcreteClass.method0( ) - called" );

      return this;
   }

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