Affine Transform如何在此代码中运行？

Question

以下代码正常运行，但我无法理解某些细节。有人可以帮我理解AffineTransform如何旋转图像吗？

package pks;

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class rotate {

    public static void main(String[] args) {
        new rotate();
    }

    public rotate() {
        EventQueue.invokeLater(new Runnable() {

           public void run() {

                final RotationPane rotationPane = new RotationPane(); // initilize object of RotationPane class
                JFrame frame = new JFrame("Test");

                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(rotationPane);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class RotationPane extends JPanel {

        private BufferedImage img;
        private BufferedImage rotated;

        private double angle;

        public RotationPane() {

            try {
                img = ImageIO.read(new File("C:\\Users\\pardeep\\Desktop\\tomb1.jpg")); // path of the image to be rotated
                setAngle(45);
            } 
            catch (IOException ex) {
            }

        }

        public void setAngle(double angle) {
            this.angle = angle;

            // Using Affine transform we will calculate the new values
            //x=vcos (theta)+wsin(theta)
            //y=vcos(theta)+ wsin(theta)

            double rads = Math.toRadians(angle);  // calculating angle in radian
            double sin = Math.abs(Math.sin(rads)),  //calculating sin theta
                   cos = Math.abs(Math.cos(rads)); // calculating cos theta

            int w = img.getWidth();
            int h = img.getHeight();

            int newWidth = (int) Math.floor(w * cos + h * sin);  //using affine transform
            int newHeight = (int) Math.floor(h * cos + w * sin);

            rotated = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_ARGB);

            Graphics2D g2d = rotated.createGraphics(); //rotating planes.....

            AffineTransform plane = new AffineTransform();

            plane.translate((newWidth - w) / 2, (newHeight - h) / 2);

            int x=w/2;
            int y=h/2;

            plane.rotate(Math.toRadians(45), x, y);

            g2d.setTransform(plane);
            g2d.drawImage(img, 0, 0, this);
        }


        public Dimension getPreferredSize() {
            return  new Dimension(800,   // setting the window size
                              800);
        }

        protected void paintComponent(Graphics g) {
            // super.paintComponent(g); no need for it

            if (rotated != null) {   // drawing image on 2 dimentional size surface
                Graphics2D g2d = (Graphics2D) g.create(); 

                int x = (getWidth() - rotated.getWidth()) / 2;
                int y = (getHeight() - rotated.getHeight()) / 2;

                g2d.drawImage(rotated, x, y, this); // overriding the method......
            }
        }        
    }    
}