Why do I get a 'constructor is undefined` error?

Why would the following code yield a compilation error (The constructor AA() is undefined)? Shouldn't it call a default constructor?

public class A{
    public A(){ }
}

public class AA extends A{
    public AA(int aa){ }
}

public class C{
    public static void main(String[] args){
        A a= new AA();
    }
}