assert(INT_1 == 1);

Gotcha.

What? You are going to use a global state for this? No, no, no! You ought to put that in a class ...

    class MyBetterrrrInteger(MyCustomNumberClass) implements ICalculatable {
      public static MyBetterrrrInteger(OtherIntegerClass num) {
        ...
        // oh did I forget to add generics to the mix? damn.
      }
    
      ...
    }