掷骰子 - ArrayIndexOutOfBounds

Question

我刚开始使用 Java 编程并编写了一个程序来滚动 x 次骰子。边数和卷数由用户输入定义。该程序以JTable 格式给出每个数字的绝对频率和相对频率。在您为边数和卷数选择大数字之前，一切正常。我收到了ArrayIndexOutOfBoundsException，但在代码中找不到任何相应的错误。

package rolling;

import java.awt.*;
import java.util.*;
import javax.swing.*;
import javax.swing.table.TableCellRenderer;
import javax.swing.JOptionPane;

public class RollDice extends JPanel {

    private static final long serialVersionUID = -6332129624300946462L;
    JTable jt;
    int i, k, j; //Counter for loops

    /*========== CONSTRUCTOR CREATES TABLE OBJECT ==========*/  
    public RollDice(int[] trial, int[] outcomes, int[] dice_numbers,
    int[] count, float[] Rel_frequencies){

        String[] columnNames = {"Number of trial", "Outcome", "Dice Numbers",
                                "Absolute Frequencies", "Relative Frequencies"};

        Object[][] input = new Object[trial.length][columnNames.length];

        for (i=0; i<trial.length; i++){
            input[i][0] = trial[i];
        }
        for (i=0; i<outcomes.length; i++){
            input[i][1] = outcomes[i];
        }
        for (i=0; i<dice_numbers.length; i++){
            input[i][2] = dice_numbers[i];
        }
        for (i=0; i<count.length; i++){
            input[i][3] = count[i];
        }
        for (i=0; i<Rel_frequencies.length; i++){
            input[i][4] = Rel_frequencies[i];
        }

        /*Checking the outcome!
        for (i=0; i<trial.length; i++){
            System.out.println();
            for (k=0; k<columnNames.length; k++){
            System.out.printf("%d\t", input[i][k]);
            }
        }*/
        jt = new JTable(input,columnNames)
        {
            /**
             * 
             */
            private static final long serialVersionUID = 1L;

            public boolean isCellEditable(int input, int columns)
            {
                return false;
            }
            public Component prepareRenderer(TableCellRenderer r, int input,
            int columns){
                Component c = super.prepareRenderer(r, input, columns);

                if (input %2 == 0){
                    c.setBackground(Color.WHITE);
                }
                else{
                    c.setBackground(Color.LIGHT_GRAY);
                }
                if (isCellSelected(input, columns)){
                    c.setBackground(Color.YELLOW);
                }
                return c;
                }
        };

        jt.setPreferredScrollableViewportSize(new Dimension(450, 600));
        jt.setFillsViewportHeight(true);

        JScrollPane jps = new JScrollPane(jt);
        add(jps);
    }

    public static int[] roll_dice(int sides, int rolls){
        int[] outcomes = new int[rolls];
        int i; //Counter for accessing array position (element)
        for (i=0; i<rolls; i++){
            outcomes[i] = (int)(1 + Math.random() * sides);
        }
        return outcomes;
    }

    public static int[] Frequency_count(int[] outcomes, int sides){
        int[] count = new int[sides];
        int i;
        int j, k = 0;
        for(i=1; i<=sides; i++){
            for(j=0; j<outcomes.length; j++){
                if (outcomes[j] == i){
                    count[k]++;
                }
            }
            //System.out.printf("%d \t %d\n",i, count[k]);
            k++;
        }
        return count;
    }

    public static float[] Relative_frequencies(int[] count, int sides, 
    int rolls){
        int i;
        float[] Array = new float [sides];
        for(i=0; i<sides; i++){
            Array[i] = (float)count[i] / rolls * 100;
            //String.format("%.3f", (float)Array[i]);
            //System.out.printf("%d \t %.2f\n",i+1, Array[i]);
        }
        return Array;
    }

    public static void main(String[] args) {
        /*=========USER INPUT via GUI: DECISION ON HOW MANY TIMES
           THE DICE IS ROLLED===*
         *=========     AND HOW MANY SIDES THE DICE HAS  ===*/

        String fn = JOptionPane.showInputDialog("Enter the number of sides
        of the dice");
        String sn = JOptionPane.showInputDialog("Enter the number of rolls");

        int sides = Integer.parseInt(fn); // number of sides
        int rolls = Integer.parseInt(sn); // number of rolls

        JOptionPane.showMessageDialog(null, "You rolled a " + sides + "
        sided dice " + rolls + " times!", "User Input",
        JOptionPane.INFORMATION_MESSAGE );

        /*=========GENERATING RANDOM NUMBERS (ROLLING THE DICE) WITH 
         "roll_dice" method==========
         *=========  AND COUNTING THE NO. OF TRIALS     ==========*/
        int[] outcomes = roll_dice(sides, rolls);
        int[] trial = new int[rolls];
        int[] dice_numbers = new int[sides];

        int i, k;
        k = 1;
        for(i=0; i<rolls; i++){
            trial[i] = k;
            //System.out.println(i + " " + k);
            k++;
        }
        k = 1;
        for(i=0; i<sides; i++){
            dice_numbers[i] = k;
            //System.out.println(i + " " + k);
            k++;
        }
        /*=========COUNTING THE FREQUENCIES OF EACH NUMBER==========*/
        //System.out.println("ABSOLUTE Frequencies plotted in FUNCTION:");
        int[] count = Frequency_count(outcomes, sides);
        //System.out.println("RELATIVE Frequencies plotted in FUNCTION:");
        float[] Rel_frequencies = Relative_frequencies(count, sides, rolls);


        /*=========CREATING A TABLE FORMAT WITH A JAVA 
        LIBRARY (JTABLE)==========*/
        JFrame jf = new JFrame();
        RollDice table1 = new RollDice(trial, outcomes, dice_numbers, 
        count, Rel_frequencies);
        jf.setTitle("Absolute and Relative Frequencies of numbers for
        an arbitrary Dice");
        jf.setSize(500, 700);
        jf.setVisible(true);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.add(table1);
        }
    }

Answer 1

看这里的这段代码：

Object[][] input = new Object[trial.length][columnNames.length];

for (i=0; i<trial.length; i++){
    input[i][0] = trial[i];
}
for (i=0; i<outcomes.length; i++){
    input[i][1] = outcomes[i];
}
for (i=0; i<dice_numbers.length; i++){
    input[i][2] = dice_numbers[i];
}
for (i=0; i<count.length; i++){
    input[i][3] = count[i];
}
for (i=0; i<Rel_frequencies.length; i++){
    input[i][4] = Rel_frequencies[i];
}

您已将input 2D 数组设置为特定大小，但随后您不假思索地访问它。

例如，看看这个：

int[] trial = new int[rolls];
int[] dice_numbers = new int[sides];

假设用户掷出 2 个骰子，得到一个 6 面骰子（传统骰子）。然后在第三个循环中，例如，您访问 input[i][2]，其中 i 从 0 运行到 5，但是由于 trial.length = 2，您访问的是不存在的索引。

您应该检查您的代码，以便仅在初始化期间根据给定的界限访问您的数组（我对您的任务了解不够多，无法尝试提出更好的建议）。

Answer 2

如果您的面数多于卷数，您似乎总是会面临这个问题。

您将 dice_numbers 和 Relative_Frequencies 数组初始化为长度等于边数，但您的 input 数组的第一个维度仅调整为滚动数。

然后，由于您试图将值存储在input 数组维度之外的位置，因此出现以下代码错误：

for (i=0; i<dice_numbers.length; i++){
    input[i][2] = dice_numbers[i];
}
// ...
for (i=0; i<Rel_frequencies.length; i++){
    input[i][4] = Rel_frequencies[i];
}

如果我理解您要正确实现的目标，为了快速解决问题，请将您的 input 数组的维度设置为较高者：边数或滚动数。

但是，您的程序的概念问题似乎是您试图将两个不同的数据集存储在同一个数组中，即一组关于实际滚动及其结果的数据，以及一组关于两侧的频率分布。

将这两个集合拆分为两个数组和两个数据表可能会大大有助于解决您面临的问题。