I always read some questions about which classes are the subclass of one class? for example:Frame, Container, Canvas and Applet are all subclasses of Component (with Canvas and Container being direct or immediate subclasses, while Frame and Applet are further down the hierarchy).
CheckboxGroup is a direct subclass of java.lang.Object.
How can I remember so many classes of Java?
By the way, who know something about CA(certification Authority) and digital signature? Could you dicuss with me?