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.
synchronized method doesnt allow another thread enter to the method through the same object. In your case t1 and t2 enters the method meth() through different objects mt1 and mt2. So the lock doesnt prevent t2 entering meth() while t1 executing meth() or vice versa.