Question

对于一个学校项目，我一直在进行扫雷游戏。它本质上是游戏的克隆，但是现在，当我尝试为JButtons添加动作侦听器时，我得到了nullpointerexception。有帮助吗？这是我的代码：

    import javax.swing.JFrame;
    import javax.swing.JButton;
    import javax.swing.JOptionPane;

    import java.awt.event.ActionListener;
    import java.awt.event.ActionEvent;
    import java.awt.event.MouseAdapter;
    import java.awt.event.MouseEvent;
    import java.awt.GridLayout;
    import java.awt.Dimension;
    import java.util.Random;

    public class Grid {

    public static int c, d; //Necessary for the allowance of usage within the listeners from lines 47 - 68.

    JFrame frame = new JFrame();
    public static boolean[][] isBomb;
    public static int bombProbability;

    public static JButton[][] grid;

    Random Bomb = new Random();

    public Grid(int width, int length){

        bombProbability = (int) Double.parseDouble(JOptionPane.showInputDialog("Input the likeliness of a bomb:"));

        frame.setLayout(new GridLayout(width, length));
        grid = new JButton[width][length];

        isBomb = new boolean[width + 2][length + 2];

        for(int a = 1; a <= length; a++){
            for(int b = 1; b <= width; b++){

                grid[a][b] = new JButton();             
                frame.add(grid[a][b]);

                if((Bomb.nextInt(99) + 1) <= bombProbability){
                    isBomb[a][b] = true;
                    grid[a][b].setText(String.valueOf(isBomb[a][b])); //Delete this before final product
                }
            }
        }
        frame.setTitle("Minesweeper!");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setMinimumSize(new Dimension(500, 500));
        frame.pack();
        frame.setVisible(true);

        for(c = 0; c < length; c++){
            for(d = 0; d < width; d++){
                grid[c][d].addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent arg0) {
                        if(isBomb[c][d] == true){
                            JOptionPane.showMessageDialog(null, "BOOM! You're DEAD!");
                            System.exit(0);
                        }
                        else{
                            indexCells(c,d);
                        }
                    }
                });
            }
        }
    }

    public static void indexCells(int c,int d){
        int[][] nearbyBombs = new int[c+2][d+2];

        for (int i = 1; i <= c; i++){
            for (int j = 1; j <= d; j++){
                // (ii, jj) indexes neighboring cells
                for (int ii = i - 1; ii <= i + 1; ii++){
                    for (int jj = j - 1; jj <= j + 1; jj++){
                        if (isBomb[ii][jj]){
                            nearbyBombs[i][j]++;
                        }
                    }
                }
                grid[i][j].setText(String.valueOf(nearbyBombs[i][j]));
                if(nearbyBombs[i][j] == 0){
                    for(int iii = i - 1; iii <= i + 1; iii ++){
                        for(int jjj = j - 1; jjj <= j + 1; jjj ++){
                            indexCells(iii,jjj);
                        }
                    }                   
                }
            }
        }
    }

    public static void main(String []args){
        //int columns = (int) Double.parseDouble(JOptionPane.showInputDialog(null, "Input the number of columns:"));
        //int rows = (int) Double.parseDouble(JOptionPane.showInputDialog(null, "Input the number of rows:"));

        new Grid(10, 10);
    }
}

问题在于第54行（grid[c][d].addActionListener(new ActionListener() {）。任何帮助将不胜感激。

Answer 1

首先你这样做......

for(int a = 1; a <= length; a++){
    for(int b = 1; b <= width; b++){
        grid[a][b] = new JButton();

然后你这样做......

for(c = 0; c < length; c++){
    for(d = 0; d < width; d++){
        grid[c][d].addActionListener(new ActionListener() {

但是grid[0][0]从未初始化，而且是null ...

你应该做更像......的事情。

for(int a = 0; a < length; a++){
    for(int b = 0; b < width; b++){
        grid[a][b] = new JButton();

添加ActionListener时，数组中的空指针异常

1 个答案: