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.
It depends on what you have in ApplicationResources.properties. The key is used to look up a value in ApplicationResources.properties so you would use whichever key you need to display the desired error message.