The original tutorial that you follows may have the package named java4s, and then you change to your liking stringdemoo and that's fine. But you've to change more thoroughly: more particularly, in the application context (and that's what the class attribute means if you don't get it).
And now, they did it quite rightly following basic convention of having upper case in the first letter of the java class (W) and then the B for reading more easily. You better follow that convention just not to make the letter jumping out of the paper for other readers. In any case, though it is a convention only you have to make it at least consistent everywhere as the name is case sensitive.
And then, you follow an old article which still use spring-bean v2.0, but since v2.5 or about, the context xml no longer uses DOCTYPE for its validation, but instead uses the w3c schema language. So you better update that part as well.