title: Subclass in dart forces me to call superclass constructor
body: <p>I am using the dart programming language where I have an abstract class <em>Vehicle</em> and a subclass <em>car</em></p>
  
  <pre><code>
  abstract class Vehicle {
  
    int _tires;
    String _type;
  
  
    Vehicle(int tires,String type) {
      this._tires=tires;
      this._type=type;
  
    }
  }
  </code></pre>
  
  <pre><code>class car extends Vehicle {
  
  car (int tires, String type)  {
     this._type=type;
     this._tires=tires;
    }
  
  }
  </code></pre>
  
  <p>Both Vehicle and car are in the same library yet I keep getting the error</p>
  
  <p><em>The superclass 'Vehicle' doesn't have a zero argument constructor.  Try declaring a zero argument constructor in 'Vehicle', or explicitly invoking a different constructor in 'Vehicle'.</em></p>
  
  <p>Why can I not declare a separate constructor in the car subclass? Thanks in advance!</p>