Java双重循环和条件使用stdDraw绘制图片，找不到错误。

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英文:

Java double for-loop and condition usng stdDraw to draw a picture, can not find the failure

问题

  1. 我因为大学关闭了，所以在家学习Java。最近，我试图使用StdDraw绘制图片，如您在下面的图片中所见，但我不明白为什么中间的红色圆圈丢失了。希望您能帮助我，谢谢！
  3. import java.awt.*;
  5. public class draw1 {
  7.     public static void main(String[] args) {
  8.         int n = 8;
  9.         int width = 300;
  10.         int height = 300;
  11.         int circle_x = width / n / 2;
  12.         int circle_y = height / n / 2;
  13.         int radius = 300 / n / 2;
  15.         StdDraw.setCanvasSize(width, height);
  16.         StdDraw.setXscale(0, 300);
  17.         StdDraw.setYscale(0, 300);
  18.         StdDraw.setPenRadius(0.002);
  19.         StdDraw.setPenColor(Color.blue);
  21.         for (int i = 1; i <= n; i++) {
  22.             for (int j = 1; j <= n; j++) {
  23.                 if (i == 1 || i == n) {
  24.                     if (j == 1 || j == n) {
  25.                         StdDraw.setPenColor(Color.blue);
  26.                         StdDraw.setPenRadius(0.002);
  27.                         StdDraw.circle(circle_x, circle_y, radius);
  28.                     } else if (j >= 2 && j < n) {
  29.                         StdDraw.setPenColor(Color.red);
  30.                         StdDraw.setPenRadius(0.006);
  31.                         StdDraw.circle(circle_x, circle_y, radius);
  32.                     }
  33.                 } else  {
  34.                     if (j == 1 || j == n) {
  35.                         StdDraw.setPenColor(Color.blue);
  36.                         StdDraw.setPenRadius(0.002);
  37.                         StdDraw.circle(circle_x, circle_y, radius);
  38.                     } else if (j >= 2 ) {
  39.                         if (n % 2 == 0) {
  40.                             if (j == n / 2) {
  41.                                 StdDraw.setPenColor(Color.orange);
  42.                                 StdDraw.setPenRadius(0.006);
  43.                                 StdDraw.circle(circle_x + radius, circle_y, radius);
  44.                             } else if ( (i == n / 2 )  ){
  45.                                 StdDraw.setPenColor(Color.red);
  46.                                 StdDraw.setPenRadius(0.006);
  47.                                 StdDraw.circle(circle_x, circle_y + radius, radius);
  48.                                 System.out.println(i + "=i");
  49.                             }
  50.                         } else if (n % 2 != 0) {
  51.                             if (j == n / 2 + 1) {
  52.                                 StdDraw.setPenColor(Color.orange);
  53.                                 StdDraw.setPenRadius(0.006);
  54.                                 StdDraw.circle(circle_x, circle_y, radius);
  55.                             } else if (i == n / 2 + 1) {
  56.                                 StdDraw.setPenColor(Color.orange);
  57.                                 StdDraw.setPenRadius(0.006);
  58.                                 StdDraw.circle(circle_x, circle_y, radius);
  59.                             }
  60.                         }
  61.                     }
  62.                 }
  63.                 System.out.println(j);
  64.                 circle_x = circle_x + (radius * 2);
  65.             }
  66.             circle_x = width / n / 2;
  67.             circle_y = circle_y + width / n;
  68.         }
  69.     }
  70. }
英文:

I am learning java at home since university has been closed. recently I am trying to draw a picture using StdDraw as you see in the picture below, but I don't understand, why the red circle in the middle is missing, I hope you could help me, thank you!

one red circle in the middle is missing

import java.awt.*;

public class draw1 {

  1. public static void main(String[] args) {
  2. int n = 8;
  3. int width = 300;
  4. int height = 300;
  5. int circle_x = width / n / 2;
  6. int circle_y = height / n / 2;
  7. int radius = 300 / n / 2;
  8. StdDraw.setCanvasSize(width, height);
  9. StdDraw.setXscale(0, 300);
  10. StdDraw.setYscale(0, 300);
  11. StdDraw.setPenRadius(0.002);
  12. StdDraw.setPenColor(Color.blue);
  13. for (int i = 1; i &lt;= n; i++) {
  14. for (int j = 1; j &lt;= n; j++) {
  15. if (i == 1 || i == n) {
  16. if (j == 1 || j == n) {
  17. StdDraw.setPenColor(Color.blue);
  18. StdDraw.setPenRadius(0.002);
  19. StdDraw.circle(circle_x, circle_y, radius);
  20. } else if (j &gt;= 2 &amp;&amp; j &lt; n) {
  21. StdDraw.setPenColor(Color.red);
  22. StdDraw.setPenRadius(0.006);
  23. StdDraw.circle(circle_x, circle_y, radius);
  24. }
  25. } else  {
  26. if (j == 1 || j == n) {
  27. StdDraw.setPenColor(Color.blue);
  28. StdDraw.setPenRadius(0.002);
  29. StdDraw.circle(circle_x, circle_y, radius);
  30. } else if (j &gt;= 2 ) {
  31. if (n % 2 == 0) {
  32. if (j == n / 2) {
  33. StdDraw.setPenColor(Color.orange);
  34. StdDraw.setPenRadius(0.006);
  35. StdDraw.circle(circle_x + radius, circle_y, radius);
  36. } else if ( (i == n / 2 )  ){
  37. StdDraw.setPenColor(Color.red);
  38. StdDraw.setPenRadius(0.006);
  39. StdDraw.circle(circle_x, circle_y + radius, radius);
  40. System.out.println(i + &quot;=i&quot;);
  41. }
  42. } else if (n % 2 != 0) {
  43. if (j == n / 2 + 1) {
  44. StdDraw.setPenColor(Color.orange);
  45. StdDraw.setPenRadius(0.006);
  46. StdDraw.circle(circle_x, circle_y, radius);
  47. } else if (i == n / 2 + 1) {
  48. StdDraw.setPenColor(Color.orange);
  49. StdDraw.setPenRadius(0.006);
  50. StdDraw.circle(circle_x, circle_y, radius);
  51. }
  52. }
  53. }
  54. }
  55. System.out.println(j);
  56. circle_x = circle_x + (radius * 2);
  57. }
  58. circle_x = width / n / 2;
  59. circle_y = circle_y + width / n;
  60. }
  61. }
  62. }

答案1

得分: 0

  1. 我认为这可能是你的问题。
  3. if (n % 2 == 0) {
  4.     if (j == n / 2) {
  5.         StdDraw.setPenColor(Color.orange);
  6.         StdDraw.setPenRadius(0.006);
  7.         StdDraw.circle(circle_x + radius, circle_y, radius);
  8.     } else if ( (i == n / 2 )  ){    &lt;---- 可能是你的问题处
  9.         StdDraw.setPenColor(Color.red);
  10.         StdDraw.setPenRadius(0.006);
  11.         StdDraw.circle(circle_x, circle_y + radius, radius);
  12.         System.out.println(i + "=i");
  13.     }
  14. }
  16. 在某种情况下，i和j的值相同。在你的情况下，它是4。
  17. 如果i和j都等于4，则代码将始终进入第一个 `if (j == n/2)`，而不会执行 `else if...`。所以基本上你要求的红色圆将不会被绘制。
  19. 顺便说一下：`n%2==0` 的检查实际上是无用的，因为你没有改变n的值（它始终为8）。因此，你的最后一段代码永远不会被执行：
  21. } else if (n % 2 != 0) {
  22.     if (j == n / 2 + 1) {
  23.         StdDraw.setPenColor(Color.orange);
  24.         StdDraw.setPenRadius(0.006);
  25.         StdDraw.circle(circle_x, circle_y, radius);
  26.     } else if (i == n / 2 + 1) {
  27.         StdDraw.setPenColor(Color.orange);
  28.         StdDraw.setPenRadius(0.006);
  29.         StdDraw.circle(circle_x, circle_y, radius);
  30.     }
  31. }
  33. 虽然不保证，但根据你的代码，这可能是原因。
英文:

I think this might be your problem.

  1.                 if (n % 2 == 0) {
  2. if (j == n / 2) {
  3. StdDraw.setPenColor(Color.orange);
  4. StdDraw.setPenRadius(0.006);
  5. StdDraw.circle(circle_x + radius, circle_y, radius);
  6. } else if ( (i == n / 2 )  ){    &lt;---- HERE MIGHT BE YOUR PROBLEM
  7. StdDraw.setPenColor(Color.red);
  8. StdDraw.setPenRadius(0.006);
  9. StdDraw.circle(circle_x, circle_y + radius, radius);
  10. System.out.println(i + &quot;=i&quot;);
  11. }

There is one case in which i and j are the same value. In your case it is 4.
If i and j both equals to 4 the code will always go into the first if (j == n/2) and will not execute the else if... So basically the red circle you asked for will not be drawn.

Btw: The n%2==0 check is practically useless because you are not changing the value of n (it is always 8). So your last code will never be executed:

  1.                 } else if (n % 2 != 0) {
  2. if (j == n / 2 + 1) {
  3. StdDraw.setPenColor(Color.orange);
  4. StdDraw.setPenRadius(0.006);
  5. StdDraw.circle(circle_x, circle_y, radius);
  6. } else if (i == n / 2 + 1) {
  7. StdDraw.setPenColor(Color.orange);
  8. StdDraw.setPenRadius(0.006);
  9. StdDraw.circle(circle_x, circle_y, radius);
  10. }
  11. }

No guarantee though but based on your code that might be the reason.

huangapple
  • 本文由 发表于 2020年4月6日 22:04:48
  • 转载请务必保留本文链接：https://go.coder-hub.com/61061656.html
  • conditional-statements
  • for-loop
  • java
  • stddraw
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