Inheritance in OO programming (AS3)

Question

Hi there,
I've been reading a book on AS3 and am getting to the point where the code that I copy from the book doesn't work on machine for some reason.  The error message is
No default constructor found in base class Vehicle
Below the code for the classes I've got and added some comments in there.
Vehicle class extends MovieClip..
package  {
    import flash.display.MovieClip;
    import flash.display.Sprite;
    import flash.events.*;
    public class Vehicle extends MovieClip{
        public var gasMileage:Number;
        public var milesTraveled:Number = 0;
        public var availableFuel:Number;
        public var _go:Boolean;
        public function Vehicle(mpg:Number, fuel:Number) {
            gasMileage = mpg;
            availableFuel = fuel;
            trace("available fuel: ", availableFuel, "... Gas Mileage:", gasMileage);
            this.addEventListener(Event.ENTER_FRAME,onLoop,false,0,true);
        public function onLoop(evt:Event):void{
            if(_go){
                this.availableFuel -= 1;
                this.milesTraveled += gasMileage;
                if( this.availableFuel < 1){
                    this.removeEventListener(Event.ENTER_FRAME, onLoop);
            trace(this, "miles traveled: " + milesTraveled, "available fuel: " +availableFuel);
        public function go():void{
            _go = true;
Car extends Vehicle which should be able to use all its functions without the Vehicle constructor. The error message is
package  {
    import  flash.display.MovieClip;
    import flash.events.Event;
    public class Car extends Vehicle{
        public function Car(mpg:Number, fuel:Number){
          trace("hello car");
               This  seems to fix the problem becuase apparently the Vehicle constructor gets called and needs the parameters passed to it.
               The book I read doesn't call the super function on Vehicle??
               and this function throws my program in an infinite loop.
          //super(5,65);              
Thanks..

Answer 1

When you run super() on a class that extends another, you are actually running their constructor, in addition to yours.
Your Vehicle has an ENTER_FRAME loop you're performing if its constructor is run. When you super, you call that and context goes insane. Simply remove that loop from Vehicle's constructor and add it into your "Car" class if you need it there. Otherwise be careful what you place inside a constructor you plan on running a super on.
In this case your Vehicle and Car both do exactly the same thing (so far). There's no reason not to just call super(). Just set the "Car" class's mpg and fuel using super because those variables were absorbed from the base class.
Base classes shared properties and methods come along for the ride. You really should just focus on what makes "Car" different from vehicle.
You can set them explicitly without declaring them in Car.
package {
// ... etc
public class Car extends Vehicle
// absorbed properties
public function Car(mpg:Number, fuel:Number)
    super(mpg,fuel);
    // these aren't declared here, they're absorbed via the extended class
    trace(gasMileage + ", " + availableFuel);