First use the vaadin and have no idea about the AbstractComponentContainer

I am studying the Events with Listeners

public class TheButtons extends CustomComponent implements Button.ClickListener {
Button thebutton;
Button secondbutton;
/** Creates two buttons in given container. */
public TheButtons(AbstractComponentContainer container) {
thebutton = new Button ("Do not push this button");
thebutton.addListener(this);
container.addComponent(thebutton);
secondbutton = new Button ("I am a button too");
secondbutton.addListener(this);
container.addComponent (secondbutton);
}
/** Handle button click events from the two buttons. */
public void buttonClick (Button.ClickEvent event) {
if (event.getButton() == thebutton)
thebutton.setCaption("Do not push this button again");
else if (event.getButton() == secondbutton)
secondbutton.setCaption("I am not a number");
}
}
The next is my application

public class TheButtonsApplication extends Application {
private static final long serialVersionUID = 2255770134219573908L;
@Override
public void init(){
/** Do not know where this is used correctly */
AbstractComponentContainer ac=new CustomComponent();
Window mainWindow=new Window("WindowOpener Application");
mainWindow.addComponent(new TheButtons(ac));
setMainWindow(mainWindow);
}
}

I really do not understand how to use the AbstractComponentContainer