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.
When there are multiple possibilities, Java will choose the most specific method. Since String is a subclass of Object, String is more specific, so the String version will be called. The version without any arguments isn't applicable when you call the method with one argument, even when the argument is null.