Java, A Beginner's Guide, 5th Edition, 5th Edition

Raw Types and Legacy Code

Because support for generics did not exist prior to JDK 5, it was necessary for Java to provide some transition path from old, pre-generics code. Simply put, pre-generics legacy code had to remain both functional and compatible with generics. This meant that pre-generics code must be able to work with generics, and generic code must be able to work with pre-generics code.

To handle the transition to generics, Java allows a generic class to be used without any type arguments. This creates a raw type for the class. This raw type is compatible with legacy code, which has no knowledge of generics. The main drawback to using the raw type is that the type safety of generics is lost.

Here is an example that shows a raw type ...