public static void main (String [] args) {
	Display display = new Display ();
	final Shell shell = new Shell (display);
	Button button1 = new Button (shell, SWT.PUSH);
	button1.setText ("Button 1");
	final Sash sash = new Sash (shell, SWT.VERTICAL);
	Button button2 = new Button (shell, SWT.PUSH);
	button2.setText ("Button 2");
	
	final FormLayout form = new FormLayout ();
	shell.setLayout (form);
	
	FormData button1Data = new FormData ();
	button1Data.left = new FormAttachment (0, 0);
	button1Data.right = new FormAttachment (sash, 0);
	button1Data.top = new FormAttachment (0, 0);
	button1Data.bottom = new FormAttachment (100, 0);
	button1.setLayoutData (button1Data);

	final int limit = 20, percent = 50;
	final FormData sashData = new FormData ();
	sashData.left = new FormAttachment (percent, 0);
	sashData.top = new FormAttachment (0, 0);
	sashData.bottom = new FormAttachment (100, 0);
	sash.setLayoutData (sashData);
	sash.addListener (SWT.Selection, new Listener () {
		@Override
		public void handleEvent (Event e) {
			Rectangle sashRect = sash.getBounds ();
			Rectangle shellRect = shell.getClientArea ();
			int right = shellRect.width - sashRect.width - limit;
			e.x = Math.max (Math.min (e.x, right), limit);
			if (e.x != sashRect.x)  {
				sashData.left = new FormAttachment (0, e.x);
				shell.layout ();
			}
		}
	});
	
	FormData button2Data = new FormData ();
	button2Data.left = new FormAttachment (sash, 0);
	button2Data.right = new FormAttachment (100, 0);
	button2Data.top = new FormAttachment (0, 0);
	button2Data.bottom = new FormAttachment (100, 0);
	button2.setLayoutData (button2Data);
	
	shell.pack ();
	shell.open ();
	while (!shell.isDisposed ()) {
		if (!display.readAndDispatch ()) display.sleep ();
	}
	display.dispose ();
}