Java Generics and Collections

Chapter 7. Reflection

Reflection is the term for a set of features that allows a program to examine its own definition. Reflection in Java plays a role in class browsers, object inspectors, debuggers, interpreters, services such as JavaBeans™ and object serialization, and any tool that creates, inspects, or manipulates arbitrary Java objects on the fly.

Reflection has been present in Java since the beginning, but the advent of generics changes reflection in two important ways, introducing both generics for reflection and reflection for generics.

By generics for reflection we mean that some of the types used for reflection are now generic types. In particular, the class Class becomes the generic class Class<T>. This may seem confusing at first, but once understood it can make programs using reflection much clearer. Class literals and the method Object.getClass use special tricks to return more-precise type information. Generics are used to especially good effect in the reflection of annotations. We observe that the type parameter T in Class<T> should always be bound to a reifiable type, and we present a short library that can help you avoid many common cases of unchecked casts.

By reflection for generics we mean that reflection now returns information about generic types. There are new interfaces to represent generic types, including type variables, parameterized types, and wildcard types, and there are new methods that get the generic types of fields, constructors, and methods.

We explain ...