Guice

Guice is a lightweight, open source, dependency injection framework for Java 6 and higher. It was made to alleviate the need for factories and using new in your Java code. You would still need to write factories in some cases as you normally would, but with Guice your code will no longer directly depend on these factories. In most cases, they will also be easier to change, unit test and reuse.

Guice fills in a lot of the missing features in core Java, and helps to design better APIs. It also aims to make development and debugging faster and easier, enabling you to understand the code with or without tools.