矩形绕(x,y)旋转

import javax.swing.*;
import java.awt.*;
import java.util.Vector;
import java.util.logging.Logger;


public class Panel extends JPanel implements Runnable
{
    int angle=0;
    final int STEP=5;
    final int INTERVAL=100;


    public Panel()
    {
    }


    @Override
    public void run()
    {
        while (true)
        {
            try
            {
                Thread.sleep(INTERVAL);
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }


            this.repaint();


        }
    }


    public void paint(Graphics g)
    {
        super.paint(g);
        g.fillRect(0, 0, 400, 300);


        int r=20;


        Vector<Point> points=new Vector<>();
        points.add(new Point(-r,-r));
        points.add(new Point(r,-r));
        points.add(new Point(r,-2*r));
        points.add(new Point(-r,-2*r));


        Point center=new Point(100,100);


        this.drawTankAngle(points, center, g, angle);


        angle+=STEP;
    }


    private double getAngleByPoint(float x, float y)
    {
        return y>0 ? Math.acos( x / Math.sqrt(x * x + y * y)) : 2 * Math.PI - Math.acos(x / Math.sqrt(x * x + y * y));
    }


    public void drawTankAngle(Vector<Point> points, Point center, Graphics g, int angle)
    {
        int iCenterX = (int)center.getX();
        int iCenterY = (int)center.getY();


        int[] xPoints = new int[points.size()];
        int[] yPoints = new int[points.size()];


        for(int i = 0; i < points.size(); i++)
        {
            xPoints[i] = (int)(points.get(i).getX());
            yPoints[i] = (int)(points.get(i).getY());
            float x = xPoints[i];
            float y = yPoints[i];
            double d = getAngleByPoint(x, y) + angle / 360.0f * 2 * Math.PI;
            xPoints[i] = (int)(Math.abs(Math.sqrt(x * x + y * y)) * Math.cos(d)) + iCenterX;
            yPoints[i] = (int)(Math.abs(Math.sqrt(x * x + y * y)) * Math.sin(d)) + iCenterY;
        }


        g.setColor(Color.yellow);
        g.drawString("0", iCenterX, iCenterY);


        g.drawPolygon(xPoints, yPoints, xPoints.length);
    }
}