Definition
Dependency injection involves at least three elements:
- a dependent consumer,
- a declaration of a component's dependencies, defined as interface contracts,
- an injector (sometimes referred to as a provider or container) that creates instances of classes that implement a given dependency interface on request.
The dependent object describes what software component it depends on to do its work. The injector decides what concrete classes satisfy the requirements of the dependent object, and provides them to the dependent.
In conventional software development, the dependent object decides for itself what concrete classes it will use. In the dependency injection pattern, this decision is delegated to the "injector" which can choose to substitute different concrete class implementations of a dependency contract interface at run-time rather than at compile time.
Being able to make this decision at run-time rather than compile time is the key advantage of dependency injection. Multiple, different implementations of a single software component can be created at run-time and passed (injected) into the same test code. The test code can then test each different software component without being aware that what has been injected is implemented differently.
Read more about this topic: Dependency Injection
Famous quotes containing the word definition:
“It’s a rare parent who can see his or her child clearly and objectively. At a school board meeting I attended . . . the only definition of a gifted child on which everyone in the audience could agree was “mine.””
—Jane Adams (20th century)
“According to our social pyramid, all men who feel displaced racially, culturally, and/or because of economic hardships will turn on those whom they feel they can order and humiliate, usually women, children, and animals—just as they have been ordered and humiliated by those privileged few who are in power. However, this definition does not explain why there are privileged men who behave this way toward women.”
—Ana Castillo (b. 1953)
“... if, as women, we accept a philosophy of history that asserts that women are by definition assimilated into the male universal, that we can understand our past through a male lens—if we are unaware that women even have a history—we live our lives similarly unanchored, drifting in response to a veering wind of myth and bias.”
—Adrienne Rich (b. 1929)