Java Swing cardlayout when card loaded

Java Swing cardlayout when card loaded

I am using Java cardlayout to switch between cards and JPanel. When
activity starts in android I can use onLoad, or similar to check if the
activity is now open. What is the equivalent to this in swing? How can I
know if the Jpanel (Card) is now in front?
public class FirstScreen extends JPanel
{
//am I visible now?
}