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语句将永远不会起作用，因为keyCodewill仅等于触发事件的最后一个键。
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);
}
}
}
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