What differentiates Beans from typical Java classes is introspection. Tools that recognize predefined patterns in method signatures and class definitions can "look inside" a Bean to determine its properties and behavior. A Bean's state can be manipulated at the time it is being assembled as a part within a larger application. The application assembly is referred to as design time in contrast to run time. In order for this scheme to work, method signatures within Beans must follow a certain pattern in order for introspection tools to recognize how Beans can be manipulated, both at design time, and run time.
In effect, Beans publish their attributes and behaviors through special method signature patterns that are recognized by beans-aware application construction tools. However, you need not have one of these construction tools in order to build or test your beans. The pattern signatures are designed to be easily recognized by human readers as well as builder tools. One of the first things you'll learn when building beans is how to recognize and construct methods that adhere to these patterns.