PropertyResourceBundle public class PropertyResourceBundle extends ResourceBundle PropertyResourceBundle is an abstract subclass of ResourceBundle that manages resources for a locale using a set of static strings from a property file. See ResourceBundle for more information about resource bundles in general. The property file contains the keys that you use in your source code in calls to ResourceBundle.getString and similar methods, and their corresponding values, etc. The name of the property file indicates the resource bundle's family and locale. The actual keys are entirely up to your choice, so long as they are the same as the keys you use in your program to retrieve the objects from the bundle.
Keys are case-sensitive.