java - 掷骰子 - ArrayIndexOutOfBounds

Question

我刚刚开始学习 Java 编程，并编写了一个程序来掷 x 面骰子 x 次。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。一切都很顺利，直到您为侧面和卷数选择较大的数字。我收到 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

看看这部分代码:

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 2 个骰子，得到 6 面骰子(传统骰子)。然后，例如，在第三个循环中，您访问 input[i][2]，其中 i 从 0 运行到 5，但是由于 Trial.length = 2，您正在访问不存在的索引。

您应该检查您的代码，以便仅根据初始化期间给定的边界访问您的数组(我对您的任务了解不够，无法尝试提出更好的建议)。