standard controller | incorrect signature | extending classes

Question

I have:

public virtual classA{
    public classA(ApexPages.StandardController controller){}
}

 public virtual classA_Test extends classA{
     classA_Test(){}
 }

 Error in classA_Test: Method does not exist or incorrect signature: [classA].<Constructor>()

 IDE: Force.com

What is the problem here?

Answer 1

When you define a constructor that takes parameters, the default 0-argument constructor is lost.

When you instantiate classA_Test, it implicitly calls the super() constructor, which no longer exists. If you want to avoid this behavior, you need to call a different constructor that is defined, e.g.:

virtual class Vehicle
{
    Vehicle(ApexPages.StandardController controller) { /*do stuff*/ }
}
class MagicCarpet extends Vehicle
{
    MagicCarpet() { super(new ApexPages.StandardController()); }
}

Side note, you cannot inherit constructors. See: Inheriting non-implicit constructors on Apex classes.