初始化类的数组成员时出现NullPointerException

Question

我几乎无法理解代码中的异常。

package botclean;

import java.util.Scanner;
import java.lang.Math;

public class BotClean {

    private static int nodeX[], nodeY[];
    private static char[][] matrix;
    private static int dirt[], botX, botY;
    private static int number_of_dirt=0;
    private static int number_of_paths=0;
    private static Path firstpath;
    private static Path paths[];
    private static int path_counter = 0;


    public static void main(String ab[])
    {
    String s;
    matrix = new char[5][5];
    Scanner sc = new Scanner(System.in);
    botX = sc.nextInt();
    botY = sc.nextInt();


    s = sc.nextLine();
    for(int i=0; i<5; i++)
    {
    s = sc.nextLine();
    for(int j=0; j<5; j++)
    {
        matrix[i][j] = s.charAt(j);
    }
    }

    searchDirt();


    make_Paths(firstpath);


    final_Path();
    }

    private static void searchDirt()
    {

        firstpath = new Path();
        firstpath.dirtX = new int[25];
        firstpath.dirtY = new int[25];

        for(int i=0; i<5; i++)
        {
        for(int j=0; j<5; j++)
        {
        if(matrix[i][j]=='d')
            {
            firstpath.dirtX[number_of_dirt] = i;
            firstpath.dirtY[number_of_dirt] = j;
            ++number_of_dirt;
            }
        }
    }


    number_of_paths = 1;

    for(int i=2; i<number_of_dirt; i++)
    number_of_paths *= i;

    System.out.println("number_of_paths = " + number_of_paths);
    System.out.println("number_of_dirt = " + number_of_dirt);


    paths = new Path[number_of_paths];

    for(int i=0; i<number_of_paths; i++)
    {

        paths[i].dirtX = new int[number_of_dirt];
        paths[i].dirtY = new int[number_of_dirt];

    }

    }

    private static void make_Paths(Path pth)
    {
    int counter=0;

    for(int i=1; i<=number_of_dirt; i++)
    {
    for(int j=1; j<=number_of_dirt; j++)
    {
    if(i==j)
    counter = (i/j)-1;

    else if(i<j)
    counter = (i/j)+(j-1);

    else
    counter = (j/i)+j;


    paths[i-1].dirtX[counter] = pth.dirtX[j-1];
    paths[i-1].dirtY[counter] = pth.dirtY[j-1];
    }

    }
}

private static void final_Path()
{
    int steps1=0,steps2=0;

    for(int i=0; i<number_of_dirt; i++)
    {
        firstpath.dirtX[i] = paths[0].dirtX[i];
        firstpath.dirtY[i] = paths[0].dirtY[i];
    }

    for(int i=1; i<number_of_paths; i++)
    {
    for(int j=0; j<number_of_dirt; j++)
        {

        steps1 += Math.abs(botX-firstpath.dirtX[j]);
        steps1 += Math.abs(botY-firstpath.dirtY[j]);

        steps2 += Math.abs(botX-paths[i].dirtX[j]);
        steps2 += Math.abs(botY-paths[i].dirtY[j]);

        }
    if(steps1>steps2)
        {

        for(int j=0; j<number_of_dirt; j++)
            {
            firstpath.dirtX[j] = paths[i].dirtX[j];
            firstpath.dirtY[j] = paths[i].dirtY[j];
            }
        }

    steps1=0; steps2=0;
    }
}



private static class Path{
    int dirtX[];
    int dirtY[];
}

}

如果您复制粘贴代码，您将在第93行遇到NullPointerException。 声明 - ＆gt;     paths [i] .dirtX = new int [number_of_dirt];