This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Well, according to the Javadoc for StringBuffer, it doesn't have the constructor that you are using. So this should not compile.
However, assuming you have a typo... according to the same javadoc, the method is an insertion of a string at an offset. In this case, the beginning of the string buffer. In your example, you are inserting a bunch of "0" into the beginning of the string buffer.