How to uniform background on listing (LaTeX)?

Question

Hi! When I put a snippet on a listing, and chage background to gray, each character's background remains in white. How to avoid it, and show all background in gray?

My LaTeX code is:

\definecolor{lbcolor}{rgb}{0.9,0.9,0.9}  
\lstset{  
language=Java,  
tabsize=4,  
basicstyle=\ttfamily,  
backgroundcolor=\color{lbcolor},  
showstringspaces=false  
}

Thanks a lot.