旋转图像java GUI

Question

我想围绕这个椭圆形轨道旋转图像：

这是我的代码：

if(xloc >= 637 && yloc >= 275) //bottom-right quadrant image rotation statement
        {
            angle = Math.atan((double)(yloc-275)/(900-xloc));
            //radians = Math.toRadians(angle);
            //radians += Math.PI;
            radians = Math.round(radians*10000000.0)/10000000.0;
        }
        else if(xloc >= 637 && yloc <= 275) //top-right quadrant image rotation statement
        {
            angle = Math.PI - Math.atan(yloc/(900-xloc));
            //radians = Math.toRadians(angle);
            radians = Math.round(radians*10000000.0)/10000000.0;
        }
        else if(xloc <= 263 && yloc <= 275) //top-left quadrant image rotation statement
        {
            angle = Math.PI + Math.atan(yloc/xloc);
            //radians = Math.toRadians(angle);
            radians = Math.round(radians*10000000.0)/10000000.0;
        }
        else if(xloc <= 264 && yloc >= 275) //bottom-left quadrant image rotation statement
        {
            angle = (2*Math.PI) - Math.atan((yloc-275)/xloc);
            //radians = Math.toRadians(angle);
            radians = Math.round(radians*10000000.0)/10000000.0;
        }
//casting the graphics object to Graphics2D
        Graphics2D g2d = (Graphics2D)g;
        //AffineTransform object image rotation
        AffineTransform a = AffineTransform.getRotateInstance(radians,xloc,yloc);
        //moving the image at x and y locations
        a.translate(xloc,yloc);
        //drawing the user's horse chariot image and applying all transformations to the image when it is drawn
        g2d.drawImage(horse,a,null);

为什么图像不会被旋转？我应该改变什么呢？