帮我看一个swt的问题

Question

我想在 composite 上画一个框，根据composite 大小来动态变动。代码如下，大神们帮忙看看是怎么回事~
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;public class Test {
    public static void main( String[] args ) throws Exception
    {
     Display display = new Display();
        Shell shell = new Shell(display);
        shell.setText("Hello World");
        shell.setBounds(100,100,800,600);
        shell.setLayout(new FillLayout());
        
        Composite comp = new Composite(shell, SWT.NONE);
        Rectangle rect = comp.getClientArea();
final int x = rect.x;
final int y = rect.y;
final int width = rect.width;
final int height = rect.height;
        comp.addPaintListener(new PaintListener(){
         public void paintControl(PaintEvent e){
     e.gc.drawString("a",10,10);
     //这里想要画一个根据comp 大小调整的框，但是并没有按照我想的画出来
     e.gc.drawRectangle(x+5, y+5, width-10, height-10);
     }
        
        });
        shell.open();
        while(!shell.isDisposed()){
         if(!display.readAndDispatch())
         display.sleep();
        }
    }
}