为什么在我的输出中出现了 “null”? – Java

huangapple
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英文:

Why is null appearing in my output? - Java

问题

以下是您提供的代码的翻译部分：

  1. 我正在编写这个程序，突然在输出中出现了 null：
  3.      1-10 |null**********
  4.     
  5.     11-20 |null**********
  6.     
  7.     21-30 |null
  8.     
  9.     31-40 |null
  10.     
  11.     41-50 |null
  12.     
  13. 应该是这样的：
  14.     
  15.      1-10 |**********
  16.     
  17.     11-20 |**********
  18.     
  19.     21-30 |
  20.     
  21.     31-40 |
  22.     
  23.     41-50 |
  25. 这是我的代码：
  27.     import java.util.Arrays;
  28.     
  29.     public class Ex4Method {
  30.     
  31.         public void Average(int[] a) {
  32.     
  33.             int total = 0;
  34.     
  35.             for (int i = 0; i < a.length; i++) {
  36.                 total = total + a[i];
  37.             }
  38.     
  39.             int average = total / a.length;
  40.     
  41.             System.out.println(" ");
  42.             System.out.println("平均值：" + average);
  43.         }
  44.     
  45.         public void MaxAndRange(int[] b) {
  46.     
  47.             int min = b[0];
  48.             int max = b[0];
  49.     
  50.             for (int i = 0; i <= 19; i++) {
  51.                 //System.out.println(i);
  52.                 if (b[i] < min) {
  53.                     min = b[i];
  54.                 }
  55.                 if (b[i] > max) {
  56.                     max = b[i];
  57.                 }
  58.             }
  59.             int range = max - min;
  60.             System.out.println("最大数：" + max);
  61.             System.out.println("范围：" + range);
  62.     
  63.         }
  64.     
  65.         public void Median(int[] c) {
  66.             Arrays.sort(c);
  67.             double median = 0;
  68.             System.out.println("中位数：" + median);
  69.         }
  70.     
  71.         public void findMedian(int a[]) {
  72.             // 首先对数组进行排序
  73.             Arrays.sort(a);
  74.             double median;
  75.             if (a.length % 2 == 0) {
  76.                 median = ((double) a[a.length / 2] + (double) a[a.length / 2 - 1]) / 2;
  77.             } else {
  78.                 median = (double) a[a.length / 2];
  79.             }
  80.     
  81.             System.out.println("中位数：" + median);
  82.         }
  83.     
  84.         public void Mode(int[] d) {
  85.     
  86.             int maxValue = 0, maxCount = 0;
  87.     
  88.             for (int i = 0; i < d.length; i++) {
  89.                 int count = 0;
  90.                 for (int j = 0; j < d.length; j++) {
  91.                     if (d[j] == d[i]) {
  92.                         count++;
  93.                     }
  94.                 }
  95.                 if (count > maxCount) {
  96.                     maxCount = count;
  97.                     maxValue = d[i];
  98.                 }
  99.             }
  100.             System.out.println("众数：" + maxValue);
  101.     
  102.     
  103.         }
  104.     
  105.         public void Histogram(int[] f) {
  106.     
  107.             String[] asterisk = new String[6];
  108.     
  109.             System.out.println("直方图：");
  110.             System.out.println(" ");
  111.             for (int i = 0; i <= f.length - 1; i++) {
  112.     
  113.                 if (f[i] >= 1 && f[i] <= 10) {
  114.                     asterisk[1] += "*";
  115.                 }
  116.                 if (f[i] >= 11 && f[i] <= 20) {
  117.                     asterisk[2] += "*";
  118.                 }
  119.                 if (f[i] >= 21 && f[i] <= 30) {
  120.                     asterisk[3] += "*";
  121.                 }
  122.                 if (f[i] >= 31 && f[i] <= 40) {
  123.                     asterisk[4] += "*";
  124.                 }
  125.                 if (f[i] >= 41 && f[i] <= 50) {
  126.                     asterisk[5] += "*";
  127.                 }
  128.             }
  129.     
  130.             System.out.println(" 1-10 |" + asterisk[1]);
  131.             System.out.println("11-20 |" + asterisk[2]);
  132.             System.out.println("21-30 |" + asterisk[3]);
  133.             System.out.println("31-40 |" + asterisk[4]);
  134.             System.out.println("41-50 |" + asterisk[5]);
  135.         }
  136.     }
  140. 主类-
  142.     
  143.     import TurtleGraphics.KeyboardReader;
  144.     
  145.     public class ArrayEx4 {
  146.     
  147.         public static void main(String[] args) {
  148.     
  149.             KeyboardReader reader = new KeyboardReader();
  150.             Ex4Method object = new Ex4Method();
  151.     
  152.             int[] nums = new int[20];
  153.             int i = 0;
  154.             System.out.print("输入一个数字 (1-50): ");
  155.             nums[i] = reader.readInt();
  156.             while (nums[i] >= 1 && nums[i] <= 50 && i < 19) {
  157.     
  158.                 i++;
  159.                 System.out.print("输入一个数字 (1-50): ");
  160.                 nums[i] = reader.readInt();
  161.                 //occurences[nums[i]]++;
  162.     
  163.             }
  164.             //for(int x=0;x<=4;x++) {
  165.             //System.out.println(occurences[x]);
  166.             //}
  167.     
  168.             object.Average(nums);
  169.             object.MaxAndRange(nums);
  170.             object.findMedian(nums);
  171.             object.Mode(nums);
  172.             object.Histogram(nums);
  173.     
  174.         }
  175.     }
  176.     
  178. 有什么建议吗？谢谢
英文:

I am writing this program and all of a sudden null appears in the output:

  1.  1-10 |null**********
  2. 11-20 |null**********
  3. 21-30 |null
  4. 31-40 |null
  5. 41-50 |null

it should be like this:

  1.  1-10 |**********
  2. 11-20 |**********
  3. 21-30 |
  4. 31-40 |
  5. 41-50 |

This is my code:

  1. import java.util.Arrays;
  2. public class Ex4Method {
  3. public void Average(int[] a) {
  4. int total = 0;
  5. for (int i = 0; i &lt; a.length; i++) {
  6. total = total + a[i];
  7. }
  8. int average = total / a.length;
  9. System.out.println(&quot; &quot;);
  10. System.out.println(&quot;Average: &quot; + average);
  11. }
  12. public void MaxAndRange(int[] b) {
  13. int min = b[0];
  14. int max = b[0];
  15. for (int i = 0; i &lt;= 19; i++) {
  16. //System.out.println(i);
  17. if (b[i] &lt; min) {
  18. min = b[i];
  19. }
  20. if (b[i] &gt; max) {
  21. max = b[i];
  22. }
  23. }
  24. int range = max - min;
  25. System.out.println(&quot;Maximum Number: &quot; + max);
  26. System.out.println(&quot;Range: &quot; + range);
  27. }
  28. public void Median(int[] c) {
  29. Arrays.sort(c);
  30. double median = 0;
  31. System.out.println(&quot;Median: &quot; + median);
  32. }
  33. public void findMedian(int a[]) {
  34. // First we sort the array 
  35. Arrays.sort(a);
  36. double median;
  37. if (a.length % 2 == 0) {
  38. median = ((double) a[a.length / 2] + (double) a[a.length / 2 - 1]) / 2;
  39. } else {
  40. median = (double) a[a.length / 2];
  41. }
  42. System.out.println(&quot;Median: &quot; + median);
  43. }
  44. public void Mode(int[] d) {
  45. int maxValue = 0, maxCount = 0;
  46. for (int i = 0; i &lt; d.length; i++) {
  47. int count = 0;
  48. for (int j = 0; j &lt; d.length; j++) {
  49. if (d[j] == d[i]) {
  50. count++;
  51. }
  52. }
  53. if (count &gt; maxCount) {
  54. maxCount = count;
  55. maxValue = d[i];
  56. }
  57. }
  58. System.out.println(&quot;Mode: &quot; + maxValue);
  59. }
  60. public void Histogram(int[] f) {
  61. String[] asterisk = new String[6];
  62. System.out.println(&quot;Histogram: &quot;);
  63. System.out.println(&quot; &quot;);
  64. for (int i = 0; i &lt;= f.length - 1; i++) {
  65. if (f[i] &gt;= 1 &amp;&amp; f[i] &lt;= 10) {
  66. asterisk[1] += &quot;*&quot;;
  67. }
  68. if (f[i] &gt;= 11 &amp;&amp; f[i] &lt;= 20) {
  69. asterisk[2] += &quot;*&quot;;
  70. }
  71. if (f[i] &gt;= 21 &amp;&amp; f[i] &lt;= 30) {
  72. asterisk[3] += &quot;*&quot;;
  73. }
  74. if (f[i] &gt;= 31 &amp;&amp; f[i] &lt;= 40) {
  75. asterisk[4] += &quot;*&quot;;
  76. }
  77. if (f[i] &gt;= 41 &amp;&amp; f[i] &lt;= 50) {
  78. asterisk[5] += &quot;*&quot;;
  79. }
  80. }
  81. System.out.println(&quot; 1-10 |&quot; + asterisk[1]);
  82. System.out.println(&quot;11-20 |&quot; + asterisk[2]);
  83. System.out.println(&quot;21-30 |&quot; + asterisk[3]);
  84. System.out.println(&quot;31-40 |&quot; + asterisk[4]);
  85. System.out.println(&quot;41-50 |&quot; + asterisk[5]);
  86. }
  87. }

MAIN CLASS-

  1. import TurtleGraphics.KeyboardReader;
  2. public class ArrayEx4 {
  3. public static void main(String[] args) {
  4. KeyboardReader reader = new KeyboardReader();
  5. Ex4Method object = new Ex4Method();
  6. int[] nums = new int[20];
  7. int i = 0;
  8. System.out.print(&quot;Enter a number (1-50): &quot;);
  9. nums[i] = reader.readInt();
  10. while (nums[i] &gt;= 1 &amp;&amp; nums[i] &lt;= 50 &amp;&amp; i &lt; 19) {
  11. i++;
  12. System.out.print(&quot;Enter a number (1-50): &quot;);
  13. nums[i] = reader.readInt();
  14. //occurences[nums[i]]++;
  15. }
  16. //for(int x=0;x&lt;=4;x++) {
  17. //System.out.println(occurences[x]);
  18. //}
  19. object.Average(nums);
  20. object.MaxAndRange(nums);
  21. object.findMedian(nums);
  22. object.Mode(nums);
  23. object.Histogram(nums);
  24. }
  25. }

Any suggestions? Thanks

答案1

得分: 2

这就是代码：

  1. public void Histogram(int[] f) {
  3.     String[] asterisk = new String[6];
  5.     System.out.println("直方图：");
  6.     System.out.println(" ");
  7.     for (int i = 0; i <= f.length - 1; i++) {
  9.         if (f[i] >= 1 && f[i] <= 10) {
  10.             asterisk[1] += "*";
  11.         }
  12.         if (f[i] >= 11 && f[i] <= 20) {
  13.             asterisk[2] += "*";
  14.         }
  15.         if (f[i] >= 21 && f[i] <= 30) {
  16.             asterisk[3] += "*";
  17.         }
  18.         if (f[i] >= 31 && f[i] <= 40) {
  19.             asterisk[4] += "*";
  20.         }
  21.         if (f[i] >= 41 && f[i] <= 50) {
  22.             asterisk[5] += "*";
  23.         }
  24.     }
  26.     System.out.println(" 1-10 |" + asterisk[1]);
  27.     System.out.println("11-20 |" + asterisk[2]);
  28.     System.out.println("21-30 |" + asterisk[3]);
  29.     System.out.println("31-40 |" + asterisk[4]);
  30.     System.out.println("41-50 |" + asterisk[5]);
  31. }
  33. 更具体地说，是这部分：
  35.     asterisk[i] += "*";
  37. 在Java中，字符串的`+`操作符表示连接，两个操作数在进行连接之前会被转换为字符串。
  39. 在最开始，`new String[6]` 填充了 `String` 类型的默认值，对于任何从 `java.lang.Object` 继承的类型来说，默认值是 `null`。当你使用操作符进行连接时，数组中的任何一个位置在第一次处理时都会遇到 `null` 值。
  41. 而且
  43.     String.valueOf(null) + "*";
  45. 会输出 `"null*"`。
  47. <details>
  48. <summary>英文:</summary>
  50. This is the code right here:
  52.     public void Histogram(int[] f) {
  54.         String[] asterisk = new String[6];
  56.         System.out.println(&quot;Histogram: &quot;);
  57.         System.out.println(&quot; &quot;);
  58.         for (int i = 0; i &lt;= f.length - 1; i++) {
  60.             if (f[i] &gt;= 1 &amp;&amp; f[i] &lt;= 10) {
  61.                 asterisk[1] += &quot;*&quot;;
  62.             }
  63.             if (f[i] &gt;= 11 &amp;&amp; f[i] &lt;= 20) {
  64.                 asterisk[2] += &quot;*&quot;;
  65.             }
  66.             if (f[i] &gt;= 21 &amp;&amp; f[i] &lt;= 30) {
  67.                 asterisk[3] += &quot;*&quot;;
  68.             }
  69.             if (f[i] &gt;= 31 &amp;&amp; f[i] &lt;= 40) {
  70.                 asterisk[4] += &quot;*&quot;;
  71.             }
  72.             if (f[i] &gt;= 41 &amp;&amp; f[i] &lt;= 50) {
  73.                 asterisk[5] += &quot;*&quot;;
  74.             }
  75.         }
  77.         System.out.println(&quot; 1-10 |&quot; + asterisk[1]);
  78.         System.out.println(&quot;11-20 |&quot; + asterisk[2]);
  79.         System.out.println(&quot;21-30 |&quot; + asterisk[3]);
  80.         System.out.println(&quot;31-40 |&quot; + asterisk[4]);
  81.         System.out.println(&quot;41-50 |&quot; + asterisk[5]);
  82.     }
  84. More specifically, this part:
  86.     asterisk[i] += &quot;*&quot;;
  88. In Java, `+` operator for strings means concatenation, and both operands are converted to strings beforehand.
  90. At the very beginning, `new String[6]` is filled with default values for `String` type, which, for any type inherited from `java.lang.Object` is a `null` value. When you concatenate using operators, the very first pass over any slot in the array will always encounter a `null` value.
  92. And
  94.     String.valueOf(null) + &quot;*&quot;
  96. will output `&quot;null*&quot;`
  99. </details>

huangapple
  • 本文由 发表于 2020年10月6日 01:51:23
  • 转载请务必保留本文链接：https://go.coder-hub.com/64213745.html
  • arrays
  • java
  • null
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