我在初始化一个对象数组网格时遇到了空指针错误。

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英文:

I am getting a null point error when initializing an array grid of objects

问题

我试图初始化一个对象数组网格，并在这样做时出现了空指针错误。应该在每次循环中调用Cell中的对象构造函数。而实际上我却得到了错误。请帮忙。

  1. public class Spread extends JPanel {
  2. 	private JPanel outputArea;
  3. 	private JTextArea numberDead;
  4. 	private JTextArea totalInfected;
  5. 	private JTextArea newInfections;
  6. 	private Integer totalDead;
  7. 	private Integer total;
  8. 	private Integer newInfected;
  9. 	private Integer length = 60;
  10. 	private Integer width = 100;
  11. 	private Cell[][] label;
  12. 	
  13. 	public void makeOutputArea() {
  14. 		int a;
  15. 		int b;
  16. 		outputArea = new JPanel(new GridLayout(length, width, -1, -1));
  17. 		outputArea.setBorder(BorderFactory.createEmptyBorder(2,2,2,2));
  19. 		for (a = 0; a < (length - 1); a++){
  20. 			for (b = 0; b < (width - 1); b++) {
  21. 				label[a][b] = new Cell(); // 空指针错误在这里。
  22. 				label[a][b].setPreferredSize(new Dimension(10, 10));
  23. 				label[a][b].setOpaque(true);
  24. 				outputArea.add(label[a][b]);
  25. 				outputArea.setVisible(true);
  26. 				if (label[a][b].getInfected() == true) ++total;
  27. 			}
  28. 		}
  29. 	}
  30. 	
  31. 	public JPanel getOutputArea() {
  32. 		return outputArea;
  33. 	}
  34. 	...其他代码继续。
  35. }

这是Cell类，它应该在数组中初始化。正如您所看到的，它有一个构造函数，应该在每次循环中调用。但实际上它给出了一个空指针错误，从未初始化每个单元格对象。

  1. import java.awt.Color;
  2. import java.util.Random;
  3. import javax.swing.JLabel;
  5. @SuppressWarnings("serial")
  6. public class Cell extends JLabel{
  7. 	private int iteration;
  8. 	private boolean infected;
  9. 	private boolean dead;
  10. 	private boolean immune;
  11. 	private Random generator = new Random(); // 随机数生成器
  12. 	private static int infectionRate = 5;
  13. 	private static int deathRate = 3;
  14. 	
  15. 	
  16. 	public void setIteration(int i) {
  17. 		iteration = i;
  18. 	}
  19. 	
  20. 	public int getIteration() {
  21. 		return iteration;
  22. 	}
  23. 	
  24. 	public void setInfected(boolean b) {
  25. 		infected = b;
  26. 	}
  27. 	
  28. 	public boolean getInfected() {
  29. 		return infected;
  30. 	}
  31. 	
  32. 	public void setDead(boolean a) {
  33. 		dead = a;
  34. 	}
  35. 	
  36. 	public boolean getDead() {
  37. 		return dead;
  38. 	}
  39. 	
  40. 	public void setImmune(boolean i) {
  41. 		immune = i;
  42. 	}
  43. 	
  44. 	public boolean getImmune() {
  45. 		return immune;
  46. 	}
  47. 	
  48. 	public Cell() {
  49. 		setImmune(false);
  50. 		setDead(false);
  51. 		setIteration(0);
  52. 		if (generator.nextInt(100) < infectionRate) {
  53. 			setInfected(true);
  54. 			setIteration(++iteration);
  55. 		}
  56. 		else setInfected(false);
  57. 		color();
  58. 	}
  59. 	
  60. 	public void color() {
  61. 		if (getInfected() == true) setBackground(Color.RED);
  62. 		else if (getDead() == true) setBackground(Color.BLACK);
  63. 		else setBackground(Color.GREEN);
  64. 	}
  65. 	
  66. 	public void updateInfection(boolean b) {
  67. 		try {
  68. 			if (getImmune() == true) return;
  69. 			else if (getDead() == true) return;
  70. 			else if (getInfected() == true) {
  71. 				setIteration(++iteration);
  72. 				if (iteration >= 4) {
  73. 					if (generator.nextInt(100) < deathRate) {
  74. 						setInfected(false);
  75. 						setDead(true);
  76. 						return;
  77. 					}
  78. 					else {
  79. 						setInfected(false);
  80. 						setImmune(true);
  81. 						return;
  82. 					}
  83. 				}
  84. 				return;
  85. 			}
  86. 			else {
  87. 				if (generator.nextInt(100) <= 75) {
  88. 					setInfected(true);
  89. 					setIteration(++iteration);
  90. 					return;
  91. 				}
  92. 				else return;
  93. 			}
  94. 		}
  95. 		finally {
  96. 			this.color();
  97. 		}
  98. 	}
  99. }
英文:

I am trying to initialize an array grid of objects and get a null point error when I do so. It should be calling the object Constructor in Cell each iteration of the loop. Instead I am getting the error. Please help.

  1. public class Spread extends JPanel {
  2. private JPanel outputArea;
  3. private JTextArea numberDead;
  4. private JTextArea totalInfected;
  5. private JTextArea newInfections;
  6. private Integer totalDead;
  7. private Integer total;
  8. private Integer newInfected;
  9. private Integer length = 60;
  10. private Integer width = 100;
  11. private Cell[][] label;
  12. public void makeOutputArea() {
  13. int a;
  14. int b;
  15. outputArea = new JPanel(new GridLayout(length, width, -1, -1));
  16. outputArea.setBorder(BorderFactory.createEmptyBorder(2,2,2,2));
  17. for (a = 0; a &lt; (length - 1); a++){
  18. for (b = 0; b &lt; (width - 1); b++)
  19. label[a][b] = new Cell(); //nullpointerror is located here.
  20. label[a][b].setPreferredSize(new Dimension(10, 10));
  21. label[a][b].setOpaque(true);
  22. outputArea.add(label[a][b]);
  23. outputArea.setVisible(true);
  24. if (label[a][b].getInfected() == true) ++total;
  25. }
  26. }
  27. public JPanel getOutputArea() {
  28. return outputArea;
  29. }
  30. ...Additional code follows.

This is the Cell class it should be initializing in the array. As you can see it has a constructor, which should be called for each loop. Instead it is giving a null pointer and never initializing each cell object.

  1. import java.awt.Color;
  2. import java.util.Random;
  3. import javax.swing.JLabel;
  4. @SuppressWarnings(&quot;serial&quot;)
  5. public class Cell extends JLabel{
  6. private int iteration;
  7. private boolean infected;
  8. private boolean dead;
  9. private boolean immune;
  10. private Random generator = new Random(); //Random number Generator
  11. private static int infectionRate = 5;
  12. private static int deathRate = 3;
  13. public void setIteration(int i) {
  14. iteration = i;
  15. }
  16. public int getIteration() {
  17. return iteration;
  18. }
  19. public void setInfected(boolean b) {
  20. infected = b;
  21. }
  22. public boolean getInfected() {
  23. return infected;
  24. }
  25. public void setDead(boolean a) {
  26. dead = a;
  27. }
  28. public boolean getDead() {
  29. return dead;
  30. }
  31. public void setImmune(boolean i) {
  32. immune = i;
  33. }
  34. public boolean getImmune() {
  35. return immune;
  36. }
  37. public Cell() {
  38. setImmune(false);
  39. setDead(false);
  40. setIteration(0);
  41. if (generator.nextInt(100) &lt; infectionRate) {
  42. setInfected(true);
  43. setIteration(++iteration);
  44. }
  45. else setInfected(false);
  46. color();
  47. }
  48. public void color() {
  49. if (getInfected() == true) setBackground(Color.RED);
  50. else if (getDead() == true) setBackground(Color.BLACK);
  51. else setBackground(Color.GREEN);
  52. }
  53. public void updateInfection(boolean b) {
  54. try {
  55. if (getImmune() == true) return;
  56. else if (getDead() == true) return;
  57. else if (getInfected() == true) {
  58. setIteration(++iteration);
  59. if (iteration &gt;=4) {
  60. if (generator.nextInt(100) &lt; deathRate) {
  61. setInfected(false);
  62. setDead(true);
  63. return;
  64. }
  65. else {
  66. setInfected(false);
  67. setImmune(true);
  68. return;
  69. }
  70. }
  71. return;
  72. }
  73. else {
  74. if (generator.nextInt(100) &lt;= 75) {
  75. setInfected(true);
  76. setIteration(++iteration);
  77. return;
  78. }
  79. else return;
  80. }
  81. }
  82. finally {
  83. this.color();
  84. }
  85. }
  86. }

答案1

得分: 0

Cell [][] label 是 Java 中的一个二维数组。
所以你首先需要为它分配内存空间。

只有在这之后，你才能执行如下代码：

  1. label[a][b] = new Cell();

这是关于如何正确为 Java 中的二维数组分配内存的大量信息，快速搜索会显示这个教程。

英文:

Cell [][] label is a two-dimentional array in java.
So you have to allocate the memory for it first.

Only then you can execute code like:

  1. label[a][b] = new Cell();

This is a lot of information about how to correctly allocate memory to 2-dimensional arrays in java, quick googling reveals this tutorial

huangapple
  • 本文由 发表于 2020年8月1日 06:26:48
  • 转载请务必保留本文链接：https://go.coder-hub.com/63199847.html
  • arrays
  • grid-layout
  • java
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