Java Reflection is a technology that looks inside a Java object at runtime and sees what variables it contains, what methods it supports, what interfaces it implements, what classes it extends—basically everything about the object that you would know at compile time.
The Reflection API is located in the java.lang.reflect package and is included in any J2SE installation. Primarily it is intended for very generic programs such as database browsers or visual code editors, but it can be used in any other applications. Reflection is for dealing with class files you know very little about ahead of time. Reflection has a very high overhead, so before using it, you should make sure that you can’t solve your problem with a simple interface, Class.forName(), and a delegate object instead.