Dealing with HashMap in Reflection

Got a school-project in java, using Reflection, I managed to handle this topic except for dealing with a HashMap.

Say we have a Shape class, and polygons that extend Shape.
Every polygon inherits an ID and a name. Here's a short example for implementation with Triangle:

Class Shape{
  private static int id_counter;
  protected ID;
  protected Shape(String name){
    ID = id_counter;
    id_counter++;
    this.name = name;
  }
}

Class Triangle {
{
  public Triangle(Sting name, Point[] vertices)
  {
    super(name);
    /* some operations to define Triangle vertices*/
  }
  public int getID()
  {
    return this.ID;
  }

It's required to perform actions on the polygons by their ID only, therefore I used a HashMap called shapesHash:

HashMap <Integer, Shape> shapesHash = new HashMap <Integer, Shape>;

Things started to get tricky when I tried to create new shapes using Reflection. In Main void, I declared as follows (skipping the required try-catch wrap):

Class<? extends Shape> myClass = Class.forName("polygonName").asSubclass(Shape.class);
// String "polygonName" is given
Constructor<?> myConstructor = myClass.getDeclaredConstructor();
Object myObject = myConstructor.newInstance(name, points);
// String "name" and Points 'points' are given
Method myMethod = myClass.getMethod("getID");
Object result = myMethod.invoke(null);
shapesHash.put( (Integer) result, (Class<? extends Shape>) myClass);   

The problem is that I tried to figure out what to put as a second argument,
instead of (Class<? extends Shape>)myClass
I tried many varieties of casting, and no casting at all - but didn't succeed (I get a compilation error).

What can I do in this situation?