[Biojava-l] codon position

[=?GB2312?B?zau54sC8?=]

Hi, everyone

I will do a program to calculate the cg skew for each codon position (first
base, second base and third base) as well as for the whole gene. For each
codon position, I found the method to get the codons:

SymbolList codons = SymbolListViews.windowedSymbolList (dna, 3);

Are there any method or package can get the first, second or third letter
from each codon?

Thanks a lot!
Lan