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这是我的第一个 Java GUI 程序，实际上只是我的第二个 Java 程序，所以请放轻松 :) 我的程序是大量谷歌搜索和阅读 Java 文档的结果。我的问题是我有一张包含 52 张卡片的精灵表，并且正在尝试使用 subImage 将这些卡片单独保存到缓冲图像数组中，并且仅出于测试目的，在窗口中显示所有 52 张卡片。该文件位于我确定的正确目录中。我相信我的问题在于我对 Jlabels 的使用，或者只是一个愚蠢的错误。无论如何，这是我的类进行精灵表拆分

 package gui;

import java.awt.GridLayout;
import java.awt.image.BufferedImage;
import java.io.File;


import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class crdimgs extends JPanel {/**
 *
 */
    static final long serialVersionUID = 1L;
    public final int width = 10;
    public final int height = 20;
    public int rows = 13;
    public int cols = 5;

    public BufferedImage image;
    File cardimg = new File("Cards.jpg");
    BufferedImage cards[];

    public void loadsplit(File loadimage){

        try{
            image = ImageIO.read(loadimage);

            } catch(Exception error){
                System.out.print("error");
              }


        cards = new BufferedImage[cols*rows];

    }

    public crdimgs() {
        loadsplit(cardimg);
        setLayout(new GridLayout(rows, cols, 1, 1));

        int x = 0;
        int y = 0;
        int subimg = 0;

        for( int i = 0; i < rows; i++)
        {
            JPanel panel = new JPanel();
            cards[subimg] = new BufferedImage(width, height, 5);
            cards[subimg] = image.getSubimage(x, y, width, height);
            panel.add(new JLabel(new ImageIcon(cards[subimg])));
            add(panel);
            x+=width;
            subimg++;
        }
        y+=height;
        x=0;
        }
    }
}

还有我的主班

package gui;
import javax.swing.JFrame;
import java.awt.Color;


public class cards extends JFrame {

    private static final long serialVersionUID = 1L;

    public cards(){

        setTitle("Poker");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(1000, 700);
        setLocationRelativeTo(null);
        this.getContentPane().setBackground(Color.GREEN);
        setVisible(true);
        setResizable(false);
        add(new crdimgs());

    }

public static void main(String[] args){
    new cards();
}
}

我目前收到的错误是：

errorException in thread "main" java.lang.NullPointerException
at gui.crdimgs.<init>(crdimgs.java:53)
at gui.cards.<init>(cards.java:22)
at gui.cards.main(cards.java:28)
4

1 回答 1

4

可能您的图像为空，可能是因为您在错误的位置寻找它，但要找出答案，请查看哪一行是 53。

建议：

  • 从小处着手，然后继续发展。在您第一次成功读取并显示单个图像之前，不要尝试进行复杂的图像处理。
  • 检查 Java 在哪里寻找图像，因为它可能不在您认为的位置。输入System.out.println(System.getProperty("user.dir"));您的代码以找出答案。
  • 将所有组件添加到 JFramesetVisible(true) 后调用。
  • 通过打印堆栈跟踪改进您的异常显示代码：（error.printStackTrace()感谢 Mad！）。

例如：

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

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

public class PlayingCardTest {


   public static void main(String[] args) {
      String pathToDeck = "http://www.jfitz.com/cards/classic-playing-cards.png";
      try {
         final List<ImageIcon> cardImgList = CreateCards.createCardIconList(pathToDeck);
         SwingUtilities.invokeLater(new Runnable() {
            public void run() {
               JFrame frame = new JFrame("Moving Cards");
               frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
               frame.add(new CardGameTable(cardImgList, frame));
               frame.pack();
               frame.setLocationRelativeTo(null);
               frame.setVisible(true);
            }
         });
      } catch (MalformedURLException e) {
         e.printStackTrace();
         System.exit(-1);
      } catch (IOException e) {
         e.printStackTrace();
         System.exit(-1);
      }
   }
}

@SuppressWarnings("serial")
class CardGameTable extends JLayeredPane {

   private static final int PREF_W = 600;
   private static final int PREF_H = 400;
   private static final Color BASE_COLOR = new Color(0, 80, 0);
   private static final int CARD_COUNT = 20;
   private static final int WIDTH_SHOWING = 20;

   private JPanel basePane = new JPanel(null);

   public CardGameTable(List<ImageIcon> cardImgList, final JFrame frame) {
      basePane.setSize(getPreferredSize());
      basePane.setBackground(BASE_COLOR);
      add(basePane, JLayeredPane.DEFAULT_LAYER);

      final MyMouseAdapter myMouseAdapter = new MyMouseAdapter(this, basePane);
      addMouseListener(myMouseAdapter);
      addMouseMotionListener(myMouseAdapter);

      for (int i = 0; i < CARD_COUNT; i++) {
         JLabel card = new JLabel(cardImgList.remove(0));
         card.setSize(card.getPreferredSize());
         int x = (PREF_W / 2) + WIDTH_SHOWING * (CARD_COUNT - 2 * i) / 2 - 
               card.getPreferredSize().width / 2;
         int y = PREF_H - card.getPreferredSize().height - WIDTH_SHOWING * 2;
         card.setLocation(x, y);
         basePane.add(card);
      }
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

}

class MyMouseAdapter extends MouseAdapter {
   private JLabel selectedCard = null;
   private JLayeredPane cardGameTable = null;
   private JPanel basePane = null;
   private int deltaX = 0;
   private int deltaY = 0;

   public MyMouseAdapter(JLayeredPane gameTable, JPanel basePane) {
      this.cardGameTable = gameTable;
      this.basePane = basePane;
   }

   @Override
   public void mousePressed(MouseEvent mEvt) {
      Component comp = basePane.getComponentAt(mEvt.getPoint());
      if (comp != null && comp instanceof JLabel) {
         selectedCard = (JLabel) comp;
         basePane.remove(selectedCard);
         basePane.revalidate();
         basePane.repaint();

         cardGameTable.add(selectedCard, JLayeredPane.DRAG_LAYER);
         cardGameTable.revalidate();
         cardGameTable.repaint();
         deltaX = mEvt.getX() - selectedCard.getX();
         deltaY = mEvt.getY() - selectedCard.getY();
      }
   }

   @Override
   public void mouseReleased(MouseEvent mEvt) {
      if (selectedCard != null) {
         cardGameTable.remove(selectedCard);
         cardGameTable.revalidate();
         cardGameTable.repaint();

         basePane.add(selectedCard, 0);
         basePane.revalidate();
         basePane.repaint();
         selectedCard = null;
      }
   }

   @Override
   public void mouseDragged(MouseEvent mEvt) {
      if (selectedCard != null) {
         int x = mEvt.getX() - deltaX;
         int y = mEvt.getY() - deltaY;
         selectedCard.setLocation(x, y);
         cardGameTable.revalidate();
         cardGameTable.repaint();
      }
   }
}

class CreateCards {
   private static final int SUIT_COUNT = 4;
   private static final int RANK_COUNT = 13;

   public static List<ImageIcon> createCardIconList(String pathToDeck)
         throws MalformedURLException, IOException {
      BufferedImage fullDeckImg = ImageIO.read(new URL(pathToDeck));
      int width = fullDeckImg.getWidth();
      int height = fullDeckImg.getHeight();
      List<ImageIcon> iconList = new ArrayList<ImageIcon>();

      for (int suit = 0; suit < SUIT_COUNT; suit++) {
         for (int rank = 0; rank < RANK_COUNT; rank++) {
            int x = (rank * width) / RANK_COUNT;
            int y = (suit * height) / SUIT_COUNT;
            int w = width / RANK_COUNT;
            int h = height / SUIT_COUNT;
            BufferedImage cardImg = fullDeckImg.getSubimage(x, y, w, h);
            iconList.add(new ImageIcon(cardImg));
         }
      }
      Collections.shuffle(iconList);
      return iconList;
   }
}

这表明：
在此处输入图像描述

于 2013-09-25T03:00:58.133 回答