Locating button by resolution

I would like to know how to locate my button location by resolution.

I got a resolution using Toolkit. like

Dimension screenSize = getDefaultToolkit().getScreenSize();

Also, I divided resolution to make a button size like

int button_width = screenSize.width / 10;

But, I want to locate my button at the lower part of a screen. 
Also, I want to make unchangeable location when I change my screen size like UI.
What should I do?