Problem extending a class

[Ramandeep]

Hi I have coded the following class which is ment to extend the registeredList class (shown in my previous post) but I get an error when trying to run the program, it says

Error (7) constructor RegisteredList() not found in class AirTrafficControl.RegisteredList.

Any ideas any one?

public class CirclingList extends RegisteredList
{
    //--------------------------------------------------------------------------

    public CirclingList(int maxPlanes)
    {
        list = new Airplane[maxPlanes];

        // initialise list
        for (int i = 0; i < list.length; i++)
        {
            list[i] = new Airplane("", 0);
        }
    }

    //--------------------------------------------------------------------------
}

[VirtuallyVB]

Without an explicit call within the subclass to a particular baseclass constructor, OO languages tend to call the default constructor of the baseclass implicitly. If this default constructor does not exist, you get the error.

A default constructor YourClass() is automatically (by default) supplied when no constructor is given, but once you supply a non default constructor, you don't get the default one supplied, so you must explicitly supply it.

class BaseClass{
public BaseClass(int i){}//public BaseClass(){} does not exist!
}

class SubClass extends BaseClass{
public SubClass(float f){}//will fail compilation BY CALLING BaseClass()
public SubClass(float f){super((int)f;}//will pass compilation because it explicitly calls the constructor requiring an int
}

Either add public BaseClass(){} to BaseClass or explicitly call another BaseClass constructor to allow it to be "found".

[Dillinger4]

Yes, always remember. "Super is often used to invoke a superclass constructor from within a subclass constructor"

Note~* If super() appears in a constructor it must appear as the first statement in the constructor.


example:

import java.awt.Color;
public class MyBox extends Box{

Color outerColor;
Color innerColor;

public MyBox(double x, double y, double width, double height, Color outer, Color inner){
super(x,y,width,height);

outer = outerColor;
inner = innerColor;
}
}

public MyBox(Color outer Color inner){
super(10,10,100,100);
outerColor = outer;
innerColor = inner;
}