inner class in AS

for example:

 package{
    public class A {
       var test:String;
       public function A()
       }
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}
 class B{

}

the code is in the same file, we call B is inner class, then how to call the constructor of class B

package
{
    public class A 
    {
       var test:String;

       public function A()
       {
          var b:B = new B();
       }
    }
}
class B
{
   public function B()
   {
       trace('class B');
   }
}