title: What is dependency injection?
body: <p>There have been several questions already posted with specific questions about <a href="http://en.wikipedia.org/wiki/Dependency_injection" rel="noreferrer">dependency injection</a>, such as when to use it and what frameworks are there for it. However,</p>
  
  <p><strong>What is dependency injection and when/why should or shouldn't it be used?</strong></p>