Hello, according to the computation done my the MyBrain Quantum Computer somewhere in Europe, the following result should be displayed when using the printClasses method: 
Jerry; - for obj
Mouse; - for mouse; obj being downcasted to mouse
GrayMouse; - for grayMouse as it was downcasted to GrayMouse from Mouse;
Jerry; for the final object.
Why the 4 Jerries for the correct solution? 
public class Solution {
    public static void main(String[] args) {
        Object obj = new Jerry(); // Add your code here

        Mouse mouse = (Mouse) obj;
        GrayMouse grayMouse = (GrayMouse) mouse;
        Jerry jerry = (Jerry) grayMouse;

        printClasses(obj, mouse, grayMouse, jerry);

    }

    public static void printClasses(Object obj, Mouse mouse, GrayMouse grayMouse, Jerry jerry) {
        System.out.println(jerry.getClass().getSimpleName());
        System.out.println(grayMouse.getClass().getSimpleName());
        System.out.println(mouse.getClass().getSimpleName());
        System.out.println(obj.getClass().getSimpleName());
    }

    static class Mouse {
    }

    static class GrayMouse extends Mouse {
    }

    static class Jerry extends GrayMouse {
    }
}