尝试使用java队列解决8个难题

我试图通过首先将电路板添加到队列中，然后以最小汉明距离将一个状态退出队列来解决8字谜问题。我有相应的函数，但我无法找到它们是否工作，因为我在第26行得到了一个空指针异常

package ai8puzzle;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.PriorityQueue;

/**
 *
 * @author Dell Inspiron
 */
public class My8Puzzle  {
    static int[] board={0,1,3,4,2,5,7,8,6};
        static int[] goal={1,2,3,4,5,6,7,8,0};
    public static void main(String[] args){

        int h;
        h = CalcHamming(board, goal);
        int prev_h = getHole();
        PriorityQueue<int[]> q = null;
        int[] b= {0,1,3,4,2,5,7,8,6};
        q.add(b);    //null pointer exception here

        while(h!=0){
            ArrayList<int[]> g;
            g = genSuccessors();
           for (int i=0; i<g.size(); i++){
               if(!q.contains(g.get(i)))
               q.offer(g.get(i));
           }
           System.out.println("board: "+Arrays.toString(q.poll()));

        }


    }

    public static ArrayList<int[]> genSuccessors()
    {
        ArrayList<int[]> successors = new ArrayList<>();
        int hole = getHole();

        // try to generate a state by sliding a tile leftwise into the hole
        // if we CAN slide into the hole
        if (hole != 0 && hole != 3 && hole != 6)
        {
            /*
             * we can slide leftwise into the hole, so generate a new state for
             * this condition and throw it into successors
             */
            swapAndStore(hole - 1, hole, successors);
        }

        // try to generate a state by sliding a tile topwise into the hole
        if (hole != 6 && hole != 7 && hole != 8)
        {
            swapAndStore(hole + 3, hole, successors);
        }

        // try to generate a state by sliding a tile bottomwise into the hole
        if (hole != 0 && hole != 1 && hole != 2)
        {
            swapAndStore(hole - 3, hole, successors);
        }
        // try to generate a state by sliding a tile rightwise into the hole
        if (hole != 2 && hole != 5 && hole != 8)
        {
            swapAndStore(hole + 1, hole, successors);
        }

        return successors;
    }

    /*
     * Switches the data at indices d1 and d2, in a copy of the current board
     * creates a new state based on this new board and pushes into s.
     */
    public static void swapAndStore(int d1, int d2, ArrayList<int[]> s)
    {
        int[] cpy = copyBoard(board);
        int temp = cpy[d1];
        cpy[d1] = board[d2];
        cpy[d2] = temp;
        s.add(cpy);

    }
        public static  int[] copyBoard(int[] state)
    {
        int[] ret = new int[9];
        System.arraycopy(state, 0, ret, 0, 9);
        return ret;
    }
    private static int CalcHamming(int[] b, int[] g) {
        int h=0;

            for(int j=0; j<9; j++){
                if(b[j]!=g[j]){
                    h++;
                }
            }

        return h; //To change body of generated methods, choose Tools | Templates.
    }

    private static int getHole() {
         int h=0;
            for(int j=0; j<3; j++){
                if(board[j]==0){
                    h=j;
                }
            }

        return h;
    }


}

封装ai8puzzle；
导入java.util.ArrayList；
导入java.util.array；
导入java.util.PriorityQueue；
/**
*
*@作者戴尔·斯皮隆
*/
公共类My8Puzzle{
静态int[]板={0,1,3,4,2,5,7,8,6}；
静态int[]目标={1,2,3,4,5,6,7,8,0}；
公共静态void main（字符串[]args）{
int-h；
h=校准（板、目标）；
int prev_h=getHole（）；
优先级队列q=null；
int[]b={0,1,3,4,2,5,7,8,6}；
q、 在此处添加（b）；//空指针异常
while（h！=0）{
ArrayList g；
g=发电机接受器（）；
对于（int i=0；i您必须在向其添加元素之前初始化
PriorityQueue q
：

    PriorityQueue<int[]> q = new PriorityQueue<int[]>();
    int[] b= {0,1,3,4,2,5,7,8,6};
    q.add(b);

PriorityQueue q=new PriorityQueue（）；
int[]b={0,1,3,4,2,5,7,8,6}；
q、 添加（b）；

如果
PriorityQueue
是一个接口，则必须使用兼容的实现进行初始化