ActionListeners 的 Stackoverflow 错误

Question

当我尝试用箭头键控制我的角色时，一切正常，但过了一会儿我得到了这个错误：

线程“AWT-EventQueue-0”java.lang.StackOverflowError 中的异常

然后

在 java.awt.AWTEventMulticaster.keyPressed(AWTEventMulticaster.java:249)

多次。我所拥有的课程甚至没有 249 行代码长，所以我不知道在哪里寻找问题。我的代码现在很乱，但如果它可以帮助任何人想出答案，我会发布它。

import javax.swing.JButton;
import javax.swing.JComponent;
import java.awt.Graphics;
import javax.swing.JFrame;
import java.awt.image.*;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;

public class mainFrame extends JPanel implements Runnable, KeyListener {
    static boolean gameIsRunning = false;
    static final int TARGET_FPS = 1;
    static int x = 100;
    static int y = 100;
    static long startTime = 0;
    static long elapsedTime = 0;
    static long waitTime = 0;
    JFrame window = new JFrame("Out from Eden");
    JPanel panel = new JPanel();
    getResources get = new getResources();
    BufferedImage player = get.getImg("player");
    static int playerVal = 0;
    static int i = 0;
    static String currentState = "";
    static int lastFacing = 0;

    public void createFrame() {
        gameIsRunning = true;
        gameStart();
    }

    public void setGame(boolean game) {
        gameIsRunning = game;
    }

    public void gameStart() {
        (new Thread(new mainFrame())).start();
    }

    public void run() {
        while (gameIsRunning == true) {
            startTime = System.nanoTime();
            updateGame();
            renderGame();
            elapsedTime = System.nanoTime() - startTime;
            waitTime = (TARGET_FPS * 10) - (elapsedTime / 1000000);

            if (waitTime < 0) {
                waitTime = 5;
            }
            try {
                Thread.sleep(waitTime);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public void updateGame() {
        if (x > 800) {
            x = 0;
        }

        if (currentState == "left") {
            x--;
        }
        if (currentState == "right") {
            x++;
        }
        player = royImage();

    }

    public BufferedImage royImage() {
        if (currentState == "right") {
            lastFacing = 2;
            i++;
            if (playerVal == 0) {
                playerVal = 1;
                i = 0;
                player = get.getImg("royWalk1");
            }
            if (playerVal == 1 && i > 20) {
                playerVal = 2;
                i = 0;
                return get.getImg("royWalk2");
            }
            if (playerVal == 2 && i > 20) {
                playerVal = 3;
                i = 0;
                player = get.getImg("royWalk3");
            }
            if (playerVal == 3 && i > 20) {
                playerVal = 4;
                i = 0;
                player = get.getImg("royWalk4");
            }
            if (playerVal == 4 && i > 20) {
                playerVal = 0;
                i = 0;
                player = get.getImg("royWalk1");
            }
        }

        if (currentState == "left") {
            lastFacing = 1;
            i++;
            if (playerVal == 0) {
                playerVal = 1;
                i = 0;
                player = get.getImg("royWalkL1");
            }
            if (playerVal == 1 && i > 20) {
                playerVal = 2;
                i = 0;
                player = get.getImg("royWalkL2");
            }
            if (playerVal == 2 && i > 20) {
                playerVal = 3;
                i = 0;
                player = get.getImg("royWalkL3");
            }
            if (playerVal == 3 && i > 20) {
                playerVal = 4;
                i = 0;
                player = get.getImg("royWalkL4");
            }
            if (playerVal == 4 && i > 20) {
                playerVal = 0;
                i = 0;
                player = get.getImg("royWalkL1");
            }
        }

        if (currentState == "null") {
            i = 0;
            playerVal = 0;
            if (lastFacing == 1) {
                player = get.getImg("playerL");
            }
            if (lastFacing == 2) {
                player = get.getImg("player");
            }
        }
        return player;
    }

    public void renderGame() {
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setBounds(30, 30, 700, 500);
        panel.setLayout(new BorderLayout());
        window.getContentPane().add(panel);
        panel.add(this);
        window.setFocusable(true);
        window.setFocusTraversalKeysEnabled(false);
        window.setVisible(true);
        window.addKeyListener(this);
        repaint();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.drawString("Hello", x, y);
        g2.drawLine(0, 63, 700, 63);
        g2.drawImage(player, x - 100, y - 100, null);
    }

    public void keyTyped(KeyEvent e) {

    }

    public void keyPressed(KeyEvent e) {
        int code = e.getKeyCode();
        if (code == KeyEvent.VK_UP) {
            currentState = "up";
        }
        if (code == KeyEvent.VK_DOWN) {
            currentState = "down";
        }
        if (code == KeyEvent.VK_LEFT) {
            currentState = "left";
        }
        if (code == KeyEvent.VK_RIGHT) {
            currentState = "right";
        }
    }

    public void keyReleased(KeyEvent e) {
        currentState = "null";
    }
}

谁能帮我弄清楚为什么会出现堆栈溢出错误以及如何避免它？

Answer 1

当您在该循环中添加一个 KeyListener 无数次时，您的 while true 循环正在让您措手不及。不要那样做，尤其是你的renderGame() 方法。你为什么还要调用一个用于多次设置 GUI 的方法？调用该方法一次会更有意义。

另外，使用 Swing Timer（Google 教程）代替您的 while 循环，避免使用 KeyListeners 来支持 Key Binding（Google 教程，并查看 this example）并执行您的设置代码只有一次。

此外，当您在非后台线程中调用 Thread.sleep(...) 和 while (true) 时，您的代码可能会导致 Swing 线程错误。为了安全起见，请改用 Swing Timer。

另外，您比较错误的字符串。不要使用== 或!= 比较字符串。请改用equals(...) 或equalsIgnoreCase(...) 方法。了解== 检查两个 对象引用 是否相同，这不是您感兴趣的。另一方面，这些方法检查两个字符串是否具有相同顺序的相同字符，这就是这里的重点。所以不是

if (fu == "bar") {
  // do something
}

做，

if ("bar".equals(fu)) {
  // do something
}

或者，

if ("bar".equalsIgnoreCase(fu)) {
  // do something
}