Dependency injection is a technique for implementing the dependency inversion principle in software design. The dependency inversion principle states that the design of a software system should be such that high-level components (such as business logic) depend on abstractions, rather than on low-level details (such as specific implementations of data access logic). In practice, dependency injection means that when designing a class or module, instead of creating its dependencies directly, it receives them through its constructor or methods as parameters. This allows the dependencies to be easily swapped out for different implementations in different scenarios, such as when unit testing the class, or when running the application in different environments. For example, consider a class that represents a shopping cart in an online store. The shopping cart class might have a dependency on a database connection, which it uses to store information about the items in the cart. Instead o...