Category : Pascal Source Code
Archive   : PASTUT.ZIP
Filename : VIRTUAL3.PAS

(* Chapter 16 - Program 3 *)
program Virtual_3;

{ ******************** class definitions **********************}

type
Vehicle = object
Wheels : integer;
Weight : real;
constructor Init(In_Wheels : integer; In_Weight : real);
procedure Message; virtual;
end;

Vehicle_Pointer = ^Vehicle;


Car = object(Vehicle)
Passenger_Load : integer;
constructor Init(In_Wheels : integer;
In_Weight : real;
People : integer);
procedure Message; virtual;
end;

Car_Pointer = ^Car;


Truck = Object(Vehicle)
Passenger_Load : integer;
Payload : real;
constructor Init(People : integer;
Max_Load : real;
In_Wheels : integer;
In_Weight : real);
procedure Message; virtual;
end;

Truck_Pointer = ^Truck;


{ ********************* class implementations ******************** }

constructor Vehicle.Init(In_Wheels : integer; In_Weight : real);
begin
Wheels := In_Wheels;
Weight := In_Weight;
end;

procedure Vehicle.Message;
begin
WriteLn('This message is from the vehicle.');
end;



constructor Car.Init(In_Wheels : integer;
In_Weight : real;
People : integer);
begin
Wheels := In_Wheels;
Weight := In_Weight;
Passenger_Load := People;
end;

procedure Car.Message;
begin
WriteLn('This message is from the car.');
end;



constructor Truck.Init(People : integer;
Max_Load : real;
In_Wheels : integer;
In_Weight : real);
begin
Passenger_Load := People;
Payload := Max_Load;
Wheels := In_Wheels;
Weight := In_Weight;
end;

procedure Truck.Message;
begin
WriteLn('This message is from the truck.');
end;



procedure Output_A_Message(VAR Machine : Vehicle_Pointer);
begin
Write('This is from Output_A_message; ');
Machine^.Message;
end;


{ ************************ main program ************************** }

var Unicycle : Vehicle_Pointer;
Sedan : Car_Pointer;
Semi : Truck_Pointer;

begin
New(Unicycle);
New(Sedan);
New(Semi);

Unicycle^.Init(1, 12.0);
Sedan^.Init(4, 2100.0, 5);
Semi^.Init(1, 25000.0, 18, 5000.0);

WriteLn;
Unicycle^.Message;
Sedan^.Message;
Semi^.Message;

WriteLn;
Output_A_Message(Unicycle);
Dispose(Unicycle);
Unicycle := Sedan;
Output_A_Message(Unicycle);
Unicycle := Semi;
Output_A_Message(Unicycle);
Dispose(Sedan);
Dispose(Semi);

end.




{ Result of execution

This message is from the vehicle.
This message is from the car.
This message is from the truck.

This is from Output_A_Message; This message is from the vehicle.
This is from Output_A_Message; This message is from the car.
This is from Output_A_Message; This message is from the truck.

}