What is introspection ?

Introspection is the ability to look at the attributes of a Java Class (including a bean) at run time.

Using introspection, I can write a method that will take any Object (of any Class), and list all of its fields and methods.

Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine. This is a relatively advanced feature and should be used only by developers who have a strong grasp of the fundamentals of the language. With that caveat in mind, reflection is a powerful technique and can enable applications to perform operations which would otherwise be impossible.