在您的评论中,您写道:
我正在使用一本使用 Java 6 的书
您指的是《Beginning Java SE 6 Game Programming, Third Edition 》一书吗?
java applet是一个容器, JPanel也是一个,因此您可以通过扩展类JPanel
而不是扩展来获得相同的结果Applet
。这意味着您可以编写常规的 java 应用程序,而无需 HTML 或 Web 浏览器。
您需要覆盖类paint()
中的方法,而不是覆盖其中的方法。Applet
paintComponent()
JPanel
下面的代码演示了通过移动鼠标来旋转一个正方形。它围绕正方形的中心点旋转正方形。当您将鼠标放在里面JPanel
并向左移动时,正方形会逆时针旋转。当您向右移动鼠标时,正方形顺时针旋转。如果您上下移动鼠标,即平行于y 轴,正方形不会旋转。
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;
public class Rotating extends JPanel implements Runnable, MouseMotionListener {
private int theta;
private int lastX = Integer.MIN_VALUE;
private BasicStroke stroke;
private JFrame frame;
/**
* Creates and returns instance of this class.
*/
public Rotating() {
stroke = new BasicStroke(2.0f);
addMouseMotionListener(this);
setPreferredSize(new Dimension(600, 600));
}
/* Start 'MouseMotionListener' interface methods. */
@Override // javax.swing.event.MouseInputListener
public void mouseDragged(MouseEvent mousEvnt) {
// Do nothing.
}
@Override // javax.swing.event.MouseInputListener
public void mouseMoved(MouseEvent mousEvnt) {
int newX = mousEvnt.getX();
if (lastX == Integer.MIN_VALUE) {
lastX = newX;
}
if (newX < lastX) {
theta--;
if (theta < 0) {
theta = 359;
}
}
else if (newX > lastX) {
theta++;
if (theta > 360) {
theta = 0;
}
}
lastX = newX;
repaint();
}
/* End 'MouseMotionListener' interface methods. */
/* Start 'Runnable' interface methods. */
@Override
public void run() {
showGui();
}
/* End 'Runnable' interface methods. */
@Override // javax.swing.JComponent
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (g instanceof Graphics2D) {
Graphics2D g2d = (Graphics2D) g;
g2d.rotate(Math.toRadians(theta), 300, 300);
g2d.setStroke(stroke);
g2d.drawRect(200, 200, 200, 200);
}
}
private void showGui() {
frame = new JFrame("Rotating");
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.add(this, BorderLayout.CENTER);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Rotating());
}
}
请注意,在覆盖方法时,paintComponent()
您几乎总是需要首先调用paintComponent()
超类中的方法。