I’m comfortable programming in Java, but am fairly new to Spring. I’ve been reading about dependency-injection/inversion of control (and using it with Spring for the past few months), but I can’t figure out the need for a separate language (xml/spring) to accomplish it.
What is wrong with creating a singleton in Java called DependencyHandler, and keeping everything in the same language? What are the advantages I get by using xml/Spring?
Dependency Injection does not require a separate language.
Spring is a framework for Java that historically required configuration in xml. Now you can configure it using xml, or java annotations.
Google’s Guice is a simple dependency injection framework that has all configuration in Java.