java - Why does setBackground to JButton does not work?

Question

I have the following simple code:

btn = new JButton();
btn.setBackground(backgroundColor)

I worked when I used:

UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsClassicLookAndFeel");

But it stopped to work after I have commented the above line. Does anybody know why it can happen and how I can set a background color to a button without the usage of an explicit Look and Feel?

ADDED

It seems to me that I need to use getBackground. But I do not know how.

Answer 1

it is necessary to set Opaque of the element to true for color to be filled

     btn = new JButton();
     btn.setOpaque(true);
     btn.setBackground(backgroundColor);