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.
You're not widening, you are narrowing. You would normally require a cast for the b = i; assignment. I can only presume that the compiler can tell that final int i = 2; implies the value of i will always be within the range of a byte. Try changing i to 128, and see whether it still works; 128 is outwith the possible range for bytes.