This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
msg is declared in the init() method. That means its scope is limited to the init() method, and you can't refer to it anywhere else. If you want to be able to refer to it in the other methods you need to declare it at the class level.
By the way, remember Java is case-sensitive and you need to be careful about case. Your Start() method won't work because it's supposed to be start().