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.
Normally not, but classes like String and the primitive wrappers (Integer, Boolean, etc) are immutable. That means that once created they can never change. It is therefore safe to share them among multiple objects, methods and threads without any problems.