为什么当我按下UP键时面板消失了？

问题和建议：

1. 您正在危险地，不需要地将AWT（例如Applet，Button，Label）和Swing（例如JPanel，JLabel）混合在一起。坚持使用Swing，摆脱AWT的所有痕迹。
2. 您直接在顶层窗口（这里是Applet）中绘画，这是一件危险的事情。别。遵循Swing图形教程，并使用JPanel的paintComponent方法绘制图形。
3. 您不会在绘画方法重写中调用super方法，这是另一件事要做的危险，并且是在没有阅读重要的相关教程的情况下试图执行此操作的另一种指示。
4. 不要使用==或比较字符串!=。改用equals(...)或equalsIgnoreCase(...)方法。理解==检查两个对象引用是否相同，这不是您感兴趣的对象。另一方面，方法检查两个Strings是否具有相同顺序的相同字符，这就是这里的要点。
5. 您试图直接设置诸如JPanel之类的组件的位置，而不考虑布局管理器。不要这样 而是移动逻辑（非组件）实体并在图形中显示移动。

您可以在此处找到Swing教程和其他Swing资源的链接：Swing信息

稍后我们可以讨论为什么您应该避免使用各种口味的小程序。

我本人会在JLabel的网格周围移动ImageIcons，而根本不直接使用绘画方法。例如，

要查看，请运行以下代码：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

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

@SuppressWarnings("serial")
public class Game2 extends JPanel {
    private static final String CPU_PATH = "https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/"
            + "Gorilla-thinclient.svg/50px-Gorilla-thinclient.svg.png";
    private static final String PERSON_PATH = "https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/"
            + "Emblem-person-blue.svg/50px-Emblem-person-blue.svg.png";
    private static final int SQR_WIDTH = 50;
    private static final int SIDES = 10;
    private static final Dimension SQR_SIZE = new Dimension(SQR_WIDTH, SQR_WIDTH);
    private static final Color DARK = new Color(149, 69, 53);
    private static final Color LIGHT = new Color(240, 220, 130);
    private JLabel[][] labelGrid = new JLabel[SIDES][SIDES];
    private Icon playerIcon;
    private Icon computerIcon;

    public Game2() throws IOException {
        // would use images instead
        playerIcon = createIcon(PERSON_PATH);
        computerIcon = createIcon(CPU_PATH);

        JPanel buttonPanel = new JPanel();
        buttonPanel.add(new JButton(new StartAction("Start", KeyEvent.VK_S)));
        buttonPanel.add(new JButton(new UpAction("Up", KeyEvent.VK_U)));
        buttonPanel.add(new JButton(new LeftAction("Left", KeyEvent.VK_L)));

        JPanel gameBrd = new JPanel(new GridLayout(SIDES, SIDES));
        gameBrd.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        for (int i = 0; i < labelGrid.length; i++) {
            for (int j = 0; j < labelGrid[i].length; j++) {
                JLabel label = new JLabel();
                label.setPreferredSize(SQR_SIZE);
                label.setOpaque(true);
                Color c = i % 2 == j % 2 ? DARK : LIGHT;
                label.setBackground(c);
                gameBrd.add(label);
                labelGrid[i][j] = label;
            }
        }

        setLayout(new BorderLayout());
        add(buttonPanel, BorderLayout.PAGE_START);
        add(gameBrd);

        // random placement, just for example
        labelGrid[4][4].setIcon(computerIcon);
        labelGrid[5][5].setIcon(playerIcon);
    }

    private Icon createIcon(String path) throws IOException {
        URL url = new URL(path);
        BufferedImage img = ImageIO.read(url);
        return new ImageIcon(img);        
    }

    private abstract class MyAction extends AbstractAction {
        public MyAction(String name, int mnemonic) {
            super(name);
            putValue(MNEMONIC_KEY, mnemonic);
        }
    }

    private class StartAction extends MyAction {
        public StartAction(String name, int mnemonic) {
            super(name, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO start game code

        }
    }

    // move all icons up
    private class UpAction extends MyAction {
        public UpAction(String name, int mnemonic) {
            super(name, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            // collection to hold label that needs to be moved
            Map<JLabel, Icon> labelMap = new HashMap<>();
            for (int i = 0; i < labelGrid.length; i++) {
                for (int j = 0; j < labelGrid[i].length; j++) {
                    Icon icon = labelGrid[i][j].getIcon();
                    if (icon != null) {
                        int newI = i == 0 ? labelGrid.length - 1 : i - 1;
                        labelGrid[i][j].setIcon(null);
                        labelMap.put(labelGrid[newI][j], icon);
                    }
                }
            }

            // move the icon after the iteration complete so as not to move it twice
            for (JLabel label : labelMap.keySet()) {
                label.setIcon(labelMap.get(label));
            }
        }
    }

    // move all icons left
    private class LeftAction extends MyAction {
        public LeftAction(String name, int mnemonic) {
            super(name, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            Map<JLabel, Icon> labelMap = new HashMap<>();
            for (int i = 0; i < labelGrid.length; i++) {
                for (int j = 0; j < labelGrid[i].length; j++) {
                    Icon icon = labelGrid[i][j].getIcon();
                    if (icon != null) {
                        int newJ = j == 0 ? labelGrid[i].length - 1 : j - 1;
                        labelGrid[i][j].setIcon(null);
                        labelMap.put(labelGrid[i][newJ], icon);
                    }
                }
            }
            for (JLabel label : labelMap.keySet()) {
                label.setIcon(labelMap.get(label));
            }
        }

    }

    private static void createAndShowGui() {
        Game2 mainPanel = null;
        try {
            mainPanel = new Game2();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(-1);
        }

        JFrame frame = new JFrame("Game2");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            createAndShowGui();
        });
    }
}