About the basic understanding of UI component

[Michael Zhou]

Hi all experts,
I have been with JSF for several weeks and so far the fundamental concept regarding the UI component still confuses me a lot!
Through my study I have learned that a UI component usually consists of three building blocks: the component class, the render, and the custom action that binds the render to the component class. Also, the render is merely responsible for visually exhibiting the component class to the client.
My question is:　is the component class merely defining the state and behavior of the UI component and not concerned about its visual presentation at all? In other words, for instance, does the component class worry about its shape, color, etc.?

Thank you very much!