8 幅拼图图片 java 帧

Question

我的 UI 代码中出现 nullreferenceexception。

idk 昨天的问题是什么，它的作品改变了一些东西，现在它不再起作用了我认为它是我创建按钮的地方

谁能看看我错在哪里

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.List;
import java.awt.MediaTracker;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.awt.image.CropImageFilter;
import java.awt.image.FilteredImageSource;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Random;
import static javafx.scene.input.KeyCode.T;

import javax.imageio.ImageIO;
import javax.swing.*;

public class Puzzle extends JFrame implements ActionListener
{
        /** JPanel variable */
        private JPanel centerPanel = new JPanel();
        private JPanel northPanel = new JPanel();
        private JPanel southPanel = new JPanel();

        /** JButton variable */
        private JButton newGame = new JButton("New Game"); 
        private JButton[] btArray = new JButton[15];
            List Collections = new List(15);



        /** JLabel variable */
        private JLabel moves = new JLabel("Moves : ");
        private JLabel label;

        private Container mainPanel = this.getContentPane();
        private int[][] pos;
        private int count;
        private String str;
            private Image source, image;

                   int width, height;



     public static <T> void shuffle(T[] array) {
    Random random = new Random();

    for (int i = array.length - 1 ; i >= 1; --i) {
        int j = random.nextInt(i);
        T temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
}

        public Puzzle()
    {
            super("Puzzle Game");
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            initUI();






        }


        public void initUI()
        {

       /*     pos = new int[][]{
                    {0, 1, 2},
                    {3, 4, 5},
                    {6, 7, 8}

          *///      };
                pos = new int[][]{
                    {0, 1, 2, 3},
                    {4, 5, 6, 7},
                        {8, 9, 10, 11},
                        {12, 13, 14, 15},

                };


         ImageIcon sid = new ImageIcon(Puzzle.class.getResource("bloem.jpg"));
        source = sid.getImage();

        width = sid.getIconWidth();
        height = sid.getIconHeight();



            /** Initialize button array */
            for (int i = 0; i < 15; i++)
            {
                image = createImage(new FilteredImageSource(source.getSource(),
                        new CropImageFilter(i*width/3, i*height/4, 
                            (width/3)+1, height/4)));

           // btArray[i] = new JButton("B" + i);
            btArray[i].setIcon(new ImageIcon(image));

         }








            /** North Panel */
            newGame.setFocusable(false);
            newGame.addActionListener(this);
            northPanel.setBackground(Color.red);
            northPanel.add(newGame);
            mainPanel.add(northPanel, BorderLayout.NORTH);

            /** South Panel */
            southPanel.add(moves);
            southPanel.setBackground(Color.LIGHT_GRAY);
            mainPanel.add(southPanel, BorderLayout.SOUTH);

            /** Game Panel */
        centerPanel.setLayout(new GridLayout(4, 4, 0, 0));
            centerPanel.setBackground(Color.BLACK);




            /** Add actionListeners to buttons */
            for (int i = 0; i < 15; i++)
        {
                btArray[i].addActionListener(this);
        }

            newGame();
        mainPanel.revalidate();
        label = new JLabel("");
            label.setBackground(Color.BLACK);
            centerPanel.add(label);
        mainPanel.add(centerPanel);
        }

        public void newGame()
        {

           count = 0;
               shuffle(btArray);

            for (int j = 14; j >= 0; j--)
            {
                centerPanel.remove(btArray[j]);

                       //   JOptionPane.showMessageDialog(null, "pfff");
            }


            for (int j = 14; j >= 0; j--)
            {
                centerPanel.add(btArray[j]);

            }
            centerPanel.revalidate();

        }



        public boolean isFinished()
            {
    {
            if ((btArray[0].getY() == btArray[1].getY() && btArray[1].getY() == btArray[2].getY()) && (btArray[3].getY() == btArray[4].getY() && btArray[4].getY() == btArray[5].getY())
                    && (btArray[6].getY() == btArray[7].getY()))
            {
                if (btArray[0].getX() == btArray[3].getX() && btArray[3].getX() == btArray[6].getX()
                        && btArray[1].getX() == btArray[4].getX() && btArray[4].getX() == btArray[7].getX()
                    && btArray[2].getX() == btArray[5].getX())
                {
                    return true;
                }
        }

            return false;
        }
            }


        public static void main(String[] args)
        {
        Puzzle puz = new Puzzle();
            puz.setBounds(20, 20, 300, 325);
            puz.setVisible(true);
        }




        public void actionPerformed(ActionEvent ae)
        {


            JButton button = (JButton) ae.getSource();
            Dimension size = button.getSize();

                if (isFinished())
            {
            JOptionPane.showMessageDialog(null, "You have Won the game");
            }

            if (ae.getSource() == newGame)
            {
                newGame();

            }



            int labelX = label.getX();
            int labelY = label.getY();
            int buttonX = button.getX();
       int buttonY = button.getY();
            int buttonPosX = buttonX / size.width;
            int buttonPosY = buttonY / size.height;
       int buttonIndex = pos[buttonPosY][buttonPosX];

       if (labelX == buttonX && (labelY - buttonY) == size.height) {

                int labelIndex = buttonIndex + 4;

                centerPanel.remove(buttonIndex);
                centerPanel.add(label, buttonIndex);
                centerPanel.add(button, labelIndex);
                centerPanel.validate();
                count++;

            }

            if (labelX == buttonX && (labelY - buttonY) == -size.height) {

                int labelIndex = buttonIndex - 4;
                centerPanel.remove(labelIndex);
                centerPanel.add(button, labelIndex);
                centerPanel.add(label, buttonIndex);
                centerPanel.validate();
                count++;

            }

        if (labelY == buttonY && (labelX - buttonX) == size.width) {

                int labelIndex = buttonIndex + 1;

                centerPanel.remove(buttonIndex);
            centerPanel.add(label, buttonIndex);
                centerPanel.add(button, labelIndex);
           centerPanel.validate();
           count++;

            }

            if (labelY == buttonY && (labelX - buttonX) == -size.width) {

                int labelIndex = buttonIndex - 1;

                centerPanel.remove(buttonIndex);
                centerPanel.add(label, labelIndex);
                centerPanel.add(button, labelIndex);
                centerPanel.validate();
                count++;

            }

        str = String.valueOf(count);
            moves.setText("Moves : " + str);


        }
    }

Answer 1

您的Null Pointer Exception可能有两个原因：

您的图片未与您的 class

或更有可能

你没有用 JButton 的实例填充你的 btArray 数组，所以它填充了默认值 (nulls) 但你试图调用 btArray[i].setIcon(imageIcon); 这意味着此代码将与 null.setIcon(imageIcon) 相同（但 null 没有任何方法或字段）。

要解决第一个问题，请确保您的文件与 Puzzle.class 位于同一目录中。

要解决第二个问题，请添加

for (int i=0; i<btArray.length;i++){
    btArray[i]=new JButton();
}

在您的 initUI 方法中实际用 JButton 个实例填充 btArray。

在 Java 8 中，您可以在声明时完成所有操作（更多信息请参见 Java 8 fill array with supplier）

private JButton[] btArray = Stream.generate(JButton::new).limit(15)
        .toArray(JButton[]::new);

8 幅拼图图片 java 帧

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