CDI caters to a very fundamental design idea, as that of dependency injection. When writing any application, you would typically define multiple classes and some relationship between them. Thus, to work with one object you would need to hand it its dependencies during its creation. When using CDI, these dependencies are provided to the object, rather than the owning object fetching them for itself. Dependency Injection (DI) leads to the owning object becoming independent of the dependency creation and lookup code, which makes it loosely coupled, and the code is testable. Both qualities, while difficult to pull off, are worth striving for.
Now, before we get into the nuts and bolts of CDI and how it helps to structure the code, let's explore what dependency injection is and what problems it helps solve with an example. Consider...