ViewPortManager.java

public class ViewPortManager {

    private HandlerRegistration windowResizeHandler;
    private List<ViewPortHelper.ViewPort> viewPorts;

    public ViewPortManager when(ViewPortHelper.ViewPort... viewPorts) {
        this.viewPorts = Arrays.asList(viewPorts);
        return this;
    }
    
    public void then(Functions.Func callback) {
        final boolean[] matches = {false};
        viewPorts.forEach(viewPort -> {
            if (ViewPortHelper.matchMedia(viewPort)) {
                matches[0] = true;
            }
        });

        if (matches[0]) {
            callback.call();
        }
        windowResizeHandler = Window.addResizeHandler(resizeEvent -> {
            if (matches[0]) {
                callback.call();
            }
        });
        
    }
}