Question

我收到的错误看起来像这样，

运行：

Exception in thread "main" java.lang.ExceptionInInitializerError
    at ao.Game.main(Game.java:11)
Caused by: java.lang.RuntimeException: Uncompilable source code - 
   ao.Panel is not abstract and does not override abstract method     
   keyReleased(java.awt.event.KeyEvent) in java.awt.event.KeyListener
    at ao.Panel.<clinit>(Panel.java:15)
    ... 1 more
Java Result: 1
BUILD SUCCESSFUL (total time: 3 seconds)

我无法弄清楚公共类的问题是什么。

下面有2个单独的文件。 Game.java Panel.java

第一档：

package ao;

import ao.Panel;
import javax.swing.JFrame;

public class Game {

    public static void main(String[] args) {
        JFrame frame = new JFrame("2D Shooter Pre-Alpha");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(new Panel());
        frame.pack();
        frame.setResizable(false);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

下一个文件：

package ao;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import java.awt.image.BufferedImage;
import javax.swing.JPanel;

/**
 *
 * @author andyoppenheimer
 */
public class Panel extends JPanel implements Runnable, KeyListener {

    // panel dimensions
    public static final int WIDTH = 320;
    public static final int HEIGHT = 240;
    public static final int SCALE = 2;
    // main loop
    private Thread thread;
    private boolean running = false;
    private int fps = 60;
    private long targetTime = 1000 / fps;
    // drawing
    private Graphics2D g;
    private BufferedImage image;

    public Panel() {
        setPreferredSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
        setFocusable(true);
        requestFocus();
    }

    public void addNotify() {
        super.addNotify();
        if (thread == null) {
            running = true;
            addKeyListener(this);
            thread = new Thread(this);
            thread.start();
        }
    }

    public void init() {

        image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        g = (Graphics2D) image.getGraphics();

    }

    public void update() {
    }

    public void draw() {
        g.clearRect(0, 0, WIDTH, HEIGHT);
    }

    public void drawToScreen() {
        Graphics g2 = getGraphics();
        g2.drawImage(image, 0, 0, WIDTH * SCALE, HEIGHT * SCALE, null);
        g2.dispose();
    }

    public void run() {

        init();

        long start;
        long elapsed;
        long wait;

        while (running == true) {
            start = System.nanoTime();

            update();
            draw();
            drawToScreen();

            elapsed = System.nanoTime() - start;
            wait = targetTime - elapsed / 1000000;

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

        }

    }

    public void KeyPressed(KeyEvent k) {
    }

    public void KeyReleased(KeyEvent k) {
    }

    public void KeyTyped(KeyEvent k) {
    }
}

Answer 1

在java方法中，从小写keyTyped keyReleased和keyPressed开始，因此您不会覆盖KeyListener方法。

您可以使用@Override注释方法如果它实际上没有覆盖，这会导致编译错误。 Section 9.6.1.4 of the JLS说：

注释类型覆盖支持早期检测此类问题。如果使用注释@Override注释方法声明，但该方法实际上不会覆盖超类中声明的任何方法，则会发生编译时错误。

您的课程定义会导致潜在错误导致

public class Panel extends JPanel implements Runnable, KeyListener

调用Panel这是令人困惑的原因已经存在java.awt.Panel所以称之为不同。实现多个类似于Single Responsability Principle的界面。一种可能的解决方案是创建内部类或匿名类。当然，如果不覆盖方法，则无需扩展JPanel。请注意，如果您使用KeyListener组件必须处于焦点并且可以聚焦并将其绑定到所有键，您可以使用KeyBindings。不要使用requestFocus代替使用requestFocusInWindow()，如果你读了api，它说不鼓励。

Answer 2

该类实现KeyListener接口，但不提供接口上指定的keyReleased，keyPressed和keyTyped方法的实现。相反，它提供了以下内容的实现：KeyReleased，KeyPressed和KeyTyped未正确套装。

公共类扩展了JPanel

2 个答案: