大米之谜-为什么“ If else”语句不能正确循环？

Question

I am sure you all know that "rice riddle" where you put a single grain of rice on the first field of a chess board and then double the amount for every subsequent field. My teacher has added a twist: every time the amount hits a certain threshold, we are to convert the amount into a different unit (eg 10 grains are 1 gram, 1000 grams are 1 kilo,...).

Here's my code:

public class Test_korn
{

    public static void main(String[] args)
    {   

     double grain ,gram, kilo, ton, container, ship;    
     int i; 

     grain = 1; 
            i = 1; 


    System.out.println( i  + ". field:  " + (int) grain + " grains" );            

     while(i <= 63)  // 2^0 = 1  bis  2^63!
        {   
        grain *=  2 ; 

        if (grain/100 <= 1)  
            {
            System.out.println( (i+1)  + ". field:  " + (int) grain + " grains" );  
            }

        else if( grain/100 > 1 && grain/10_000 <= 1 )   
            {
            gram = grain/10;    
            System.out.println( (i+1) + ". field:  " + gram + " grams" );   
            }

        else if( grain/10_000 > 1 && grain/(10_000 * 1000) <= 1)  
            {
            kilo = grain/(10 * 1000);   
            System.out.println( (i+1)  + ". field:  " + kilo + " kilogram" );       
            }

        else if( grain/(10_000 * 1000) > 1  &&  grain/(10_000 * 1000 * 1000)  <= 1 )  
            {
            ton = grain/( 10 * 1000 * 1000);    
            System.out.println( (i+1)  + ". field:  " + ton + " tons" ); 
            }

        else if(   grain/(10_000 * 1000 * 1000)  > 1   &&  grain/(10_000 * 1000 * 1000 * 1000)  <= 1  )    
            {
            container = grain/(10 * 1000 * 1000 *1000);     
            System.out.println( (i+1)  + ". field:  " + container + " container" );     
            }

        else if(  grain/(10_000 * 1000 * 1000 * 1000)  > 1 )   
            {
            ship = grain/(10000 * 1000 * 1000 * 1000 * 1000);   
            System.out.println( (i+1)  + ". field:  " + ship + "container ship" );                  
            }   

        i++;    
        }       
    }
} 

And here is the output:

1. field:  1 grains
2. field:  2 grains
3. field:  4 grains
4. field:  8 grains
5. field:  16 grains
6. field:  32 grains
7. field:  64 grains
8. field:  12.8 gram
9. field:  25.6 gram
10. field:  51.2 gram
11. field:  102.4 gram
12. field:  204.8 gram
13. field:  409.6 gram
14. field:  819.2 gram
15. field:  1.6384 kilos
16. field:  3.2768 kilos
17. field:  6.5536 kilos
18. field:  13.1072 kilos
19. field:  26.2144 kilos
20. field:  52.4288 kilos
21. field:  104.8576 kilos
22. field:  209.7152 kilos
23. field:  419.4304 kilos
24. field:  838.8608 kilos
25. field:  1.6777216 tons
26. field:  3.3554432 tons
27. field:  6.7108864 tons
28. field:  13.4217728 tons
29. field:  26.8435456 tons
30. field:  53.6870912 tons
31. field:  107.3741824 tons
32. field:  1.145373833409067 container ships
33. field:  2.290747666818134 container ships
34. field:  4.581495333636268 container ships
35. field:  9.162990667272537 container ships
36. field:  18.325981334545073 container ships
37. field:  36.651962669090146 container ships
38. field:  73.30392533818029 container ships
39. field:  146.60785067636058 container ships
40. field:  293.21570135272117 container ships
41. field:  586.4314027054423 container ships
42. field:  1172.8628054108847 container ships
43. field:  2345.7256108217694 container ships
44. field:  4691.451221643539 container ships
45. field:  9382.902443287077 container ships
46. field:  18765.804886574155 container ships
47. field:  37531.60977314831 container ships
48. field:  75063.21954629662 container ships
49. field:  150126.43909259324 container ships
50. field:  300252.8781851865 container ships
51. field:  600505.756370373 container ships
52. field:  1201011.512740746 container ships
53. field:  2402023.025481492 container ships
54. field:  4804046.050962984 container ships
55. field:  9608092.101925967 container ships
56. field:  1.9216184203851935E7 container ships
57. field:  3.843236840770387E7 container ships
58. field:  7.686473681540774E7 container ships
59. field:  1.5372947363081548E8 container ships
60. field:  3.0745894726163095E8 container ships
61. field:  6.149178945232619E8 container ships
62. field:  1.2298357890465238E9 container ships
63. field:  2.4596715780930476E9 container ships
64. field:  4.919343156186095E9 container ships

As you can see, it works as intented until the loop hits the 32nd iteration and than it goes all wrong. After looking at the code for 1 hour all I've found is that the loop runs through all iterations, but the compiler seems to have trouble with both else if s for tonnage and container. It seems that it cannot deal with the logical expression behind the && --but why? After all, it works great the other times.

It would be great if anyone could point me into the right direction, as I am currently completely lost.

Answer 1

Although you declared grain as a double which can go well beyond 2^63, your calculations like 10_000 * 1000 * 1000 will be registered as int which only range to 2,147,483,647 leading to an overflow and these high unrecognizable values. They have to be calculated as double so just add a .0 to all your multipliers, eg 10_000.0, 1000.0 and so on).