Inheritance problems with constructor

[Julius Fuchs]

Hi,

if I create a Person, a Vehicle is created; that's fine.
The problem is that if I create a Child the constuctor of Person is called
before and a Vehicle is created then a Bike is created and the variable is
overwritten. How can I prevent this?
class Person
{
protected Vehicle fVehicle;

public Person()
{
fVehicle = new Vehicle();
}
}

class Child : Person
{
public Child()
{
fVehicle = new Bike();
}
}

class Vehicle
{}

class Bike : Vehicle
{}

[Bruce Wood]

Julius Fuchs wrote:

Hi,

if I create a Person, a Vehicle is created; that's fine.
The problem is that if I create a Child the constuctor of Person is called
before and a Vehicle is created then a Bike is created and the variable is
overwritten. How can I prevent this?
class Person
{
protected Vehicle fVehicle;

public Person()
{
fVehicle = new Vehicle();
}
}

class Child : Person
{
public Child()
{
fVehicle = new Bike();
}
}

class Vehicle
{}

class Bike : Vehicle
{}

Perhaps the problem is that you don't want to create a (generic)
vehicle for a Person. What you want, I think, this:

class Person
class Adult : Person
class Child : Person
class Vehicle
class Car : Vehicle
class Bike : Vehicle

Person does not allocate a vehicle, whereas Adult creates a Car and
Child creates a Bike.

Another possibility is to supply an alternate constructor:

public Person() : this(new Vehicle)
{ }

protected Person(Vehicle v)
{
fVehicle = v;
}

then

public Child() : base(new Bike())
{
...
}

[Julius Fuchs]

Hi,

Another possibility is to supply an alternate constructor:[...]

Thank you very much! That's what I was looking for, very elegant!

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

With your current struct you cannot avoid the creation of the Vehicle in the
parent class. Note that usually this has not further effect than just
another instance to be GCed.

Now, a more elegant solution could be achieve by changing a little the
constructors.

Person:
protected Person( Vehicle v){ fVehicle = v;}
public Person():this( new Vehicle){}

Child:
public Child(): base( new Bycicle() ){}

Note that if this would have been in any other case except in the
constructors a virtual method will solve the situation.
--
--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation
"Julius Fuchs" <ju**********@yahoo.dewrote in message
news:1a*****************************@40tude.net...

Hi,

if I create a Person, a Vehicle is created; that's fine.
The problem is that if I create a Child the constuctor of Person is called
before and a Vehicle is created then a Bike is created and the variable is
overwritten. How can I prevent this?
class Person
{
protected Vehicle fVehicle;

public Person()
{
fVehicle = new Vehicle();
}
}

class Child : Person
{
public Child()
{
fVehicle = new Bike();
}
}

class Vehicle
{}

class Bike : Vehicle
{}