java - 当我按下按钮时，为什么小程序中的球不移动？

Question

我对 Java 和编程都很陌生，所以我尝试编写一个简单的程序，其唯一的工作就是让一个球用箭头键移动并用空格键跳跃。程序编译，但球没有移动。

我可能没有完全理解Applet的原理，你能给我解释一下我犯的错误吗？

小程序:

package test_game;

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class Starting_Point extends Applet implements Runnable, KeyListener {

    private static final long serialVersionUID = 1L;
    private static final int WIDTH = 700;
    private static final int HEIGHT = 300;
    Character Phil;
    Thread thread;

    @Override
    public void init() {
        setSize(WIDTH,HEIGHT);
        Phil = new Character(50, 200);
    }

    @Override
    public void start() {
        thread = new Thread(this);
        thread.start();
    }

    public void run() {
        while (true) {
            repaint();  
        }
    }

    @Override
    public void paint(Graphics arg0) {
        Phil.paint(arg0);
    }

    @Override
    public void keyPressed(KeyEvent arg0) {
        switch (arg0.getKeyCode()) {
            case (KeyEvent.VK_LEFT): Phil.setX(Phil.getX() - Phil.getDx());
                break;
            case (KeyEvent.VK_RIGHT): Phil.setX(Phil.getX() + Phil.getDx());
                break;
            case (KeyEvent.VK_SPACE): Phil.setDy(Character.gravity * Character.dt);
                Phil.setY(Phil.getY() + .5*Character.gravity*Character.dt*Character.dt + Phil.getDy()*Character.dt + Character.jump);
                break;
        }
    }

    @Override
    public void keyReleased(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }
}

角色类别:

package test_game;

import java.awt.Color;
import java.awt.Graphics;

public class Character {

    private int x;
    private int y;
    private int radius = 10;
    Graphics g;
    public static final int gravity = 15;
    private static final double dx = 4;
    public double dy;
    public static final double dt = .2;
    public static final int jump = 30;

    public Character(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public void setX(double d) {
        this.x = (int) d;
    }

    public void setY(double d) {
        this.y = (int) d;
    }

    public double getDx() {
        return dx;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    public void setDy(double dy) {
        this.dy = dy;
    }

    public double getDy() {
        return dy;
    }

    public void paint(Graphics g) {
        g.setColor(Color.black);
        g.fillOval(x, y, radius, radius);   
    }
}

Answer 1

您已在代码中定义了一个KeyListener。但是，您忘记将此事件监听器注册到组件，因此它从未被调用。

如何注册您的 KeyListener:

将以下代码放入 start() 中:

this.addKeyListener(this);

这解决了角色向左或向右移动的问题，但是跳跃并未修复，修复跳跃需要更多代码来计算您需要的正确 y+，当前代码总是添加 0(四舍五入到当您按空格键时，0 使用您使用的 (int)) 到 y 坐标。