小程序中的按键故障

Question

下面是我一直在制作的小程序，它允许用户使用箭头键在屏幕上移动一个矩形。除向下键外，所有键都起作用，它使矩形沿对角线向右下方移动。答案可能很明显；希望不会！请帮忙！谢谢！

import javax.swing.*;

import java.applet.Applet;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.net.URL;
import java.util.ArrayList;

import javax.imageio.ImageIO;

public class Move extends Applet implements KeyListener {
    private Rectangle rect;
    private ArrayList<Integer> keysDown;

public void init() {
    this.addKeyListener(this);
    keysDown = new ArrayList<Integer>();
    rect = new Rectangle(0, 0, 50, 50);
}

public void paint(Graphics g) {
    setSize(600, 400);
    Graphics2D g2 = (Graphics2D)g;
    g2.fill(rect);
}

@Override
public void keyPressed(KeyEvent e) {
    if (!keysDown.contains(e.getKeyCode()))
        keysDown.add(new Integer(e.getKeyCode()));
moveRect();
}

@Override
public void keyReleased(KeyEvent e) {
    keysDown.remove(new Integer(e.getKeyCode()));
}

public void moveRect() {
    int x = rect.x;
    int y = rect.y;
    if (keysDown.contains(KeyEvent.VK_UP)) {
        y -= 2;
    }
    if (keysDown.contains(KeyEvent.VK_DOWN)) {
        y += 2;
    }
    if (keysDown.contains(KeyEvent.VK_LEFT)) {
        x -= 2;
    }
    if (keysDown.contains(KeyEvent.VK_DOWN)) {
        x += 2;
    }
    rect.setLocation(x, y);
    repaint();
}

@Override
public void keyTyped(KeyEvent e) {

}
}

Answer 1

您在处理按键的moveRect 的if 语句中是否缺少VK_RIGHT？

我看到你有两个VK_DOWN - 当你按下向下键时，这将沿着 X 和 Y 移动矩形。

查看moveRect 方法中的这些行，注意VK_DOWN 是如何被处理两次的（而VK_RIGHT 根本没有被处理）：

if (keysDown.contains(KeyEvent.VK_UP)) {
    y -= 2;
}
if (keysDown.contains(KeyEvent.VK_DOWN)) {
    y += 2;
}
if (keysDown.contains(KeyEvent.VK_LEFT)) {
    x -= 2;
}
if (keysDown.contains(KeyEvent.VK_DOWN)) {
    x += 2;
}