使用键盘在Java中以一定角度移动圆

因为键事件将仅报告触发事件的最后一个键，所以您的最后一条

if

keyCode

相反，您应该维护每个键的“状态”并针对该状态进行处理。

import java.awt.BorderLayout;import java.awt.Color;import java.awt.Dimension;import java.awt.EventQueue;import java.awt.FontMetrics;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.event.KeyAdapter;import java.awt.event.KeyEvent;import javax.swing.Jframe;import javax.swing.JPanel;import javax.swing.UIManager;import javax.swing.UnsupportedLookAndFeelException;public class TestKeyListener01 {    public static void main(String[] args) {        new TestKeyListener01();    }    public TestKeyListener01() {        EventQueue.invokeLater(new Runnable() { @Override public void run() {     try {         UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());     } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {     }     Jframe frame = new Jframe("Testing");     frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);     frame.setLayout(new BorderLayout());     frame.add(new TestPane());     frame.pack();     frame.setLocationRelativeTo(null);     frame.setVisible(true); }        });    }    public class TestPane extends JPanel {        private boolean arrowUp = false;        private boolean arrowDown = false;        private boolean arrowLeft = false;        private boolean arrowRight = false;        public TestPane() { setFocusable(true); addKeyListener(new KeyAdapter() {     @Override     public void keyReleased(KeyEvent e) {         switch (e.getKeyCode()) {  case KeyEvent.VK_DOWN:      arrowDown = false;      break;  case KeyEvent.VK_UP:      arrowUp = false;      break;  case KeyEvent.VK_LEFT:      arrowLeft = false;      break;  case KeyEvent.VK_RIGHT:      arrowRight = false;      break;         }         repaint();     }     @Override     public void keyPressed(KeyEvent e) {         switch (e.getKeyCode()) {  case KeyEvent.VK_DOWN:      arrowDown = true;      break;  case KeyEvent.VK_UP:      arrowUp = true;      break;  case KeyEvent.VK_LEFT:      arrowLeft = true;      break;  case KeyEvent.VK_RIGHT:      arrowRight = true;      break;         }         repaint();     } });        }        @Override        public Dimension getPreferredSize() { return new Dimension(200, 200);        }        @Override        protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g.create(); FontMetrics fm = g2d.getFontMetrics(); String text = "Up"; int x = (getWidth() - fm.stringWidth(text)) / 2; int y = ((getHeight() / 2) - fm.getHeight()); draw(g2d, text, x, y, arrowUp); text = "Down"; x = (getWidth() - fm.stringWidth(text)) / 2; y = ((getHeight() / 2) + fm.getHeight()) + fm.getAscent(); draw(g2d, text, x, y, arrowDown); text = "Left"; x = (getWidth() / 2) - fm.stringWidth(text) - 4; y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent(); draw(g2d, text, x, y, arrowLeft); text = "Right"; x = (getWidth() / 2) + 4; y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent(); draw(g2d, text, x, y, arrowRight); g2d.dispose();        }        protected void draw(Graphics2D g2d, String text, int x, int y, boolean pressed) { g2d.setColor(pressed ? Color.BLACK : Color.GRAY); g2d.drawString(text, x, y);        }    }}

我还建议

KeyListener

KeyListener