Something

		// nbody forces
		SpinButton spGravitationalConstant = (SpinButton) glade.getWidget("spGravitationalConstant");
		
		// ok button
		Button okButton = (Button) glade.getWidget("okbuttonLayoutProperties");
		
		okButton.addListener(new ButtonListener() {
			public void buttonEvent(ButtonEvent event) {
				if (event.isOfType(ButtonEvent.Type.CLICK)) {
					spGravitationalConstant.getValue();
				}
			}
		});