Explicit Dependencies Principle

Have you ever wanted to try to cook a recipe only to find out that it left off an ingredient in the shopping list? Steve ran into that with a spaghetti Bolognese recipe, where an ingredient was left off. When all of the ingredients are called out explicitly, it's easier to follow the recipe.

Much like ingredients to a recipe, it's important to understand dependencies of classes/packages/libraries/frameworks before working with them. Implicit dependencies and transitive dependencies can make it harder to work with classes/packages/libraries/frameworks. This is why there is the Explicit Dependencies Principle.

Methods and classes should explicitly require (typically through method parameters or constructor parameters) any collaborating objects they need in order to function correctly.

If your classes require other classes to perform their operations, these other classes are dependencies.  These dependencies are implicit if they exist only in the code within your class, and not in its public interface.  Explicit dependencies appear most often in an object's constructor, for class-level dependencies, or in a particular method's parameter list, for more local dependencies.

Leave a Comment