Inversion of Control (IoC) is a design principle where the control flow of a program is inverted: instead of the application controlling the flow of execution, it delegates control to an external framework or container. This helps in achieving loose coupling and better modularization of code. In this tutorial, we’ll explore the concept of IoC in Java without relying on the Spring Framework.
The fundamental idea behind IoC is to invert the flow of control regarding the creation and management of objects. In a traditional approach, a class is responsible for creating instances of its dependencies. With IoC, the responsibility for creating and managing objects is shifted to an external container.
Example Implementation in Java:
Let’s consider a simple example where we have a Car class that depends on an Engine:
In a non-IoC scenario, the Car class would be responsible for creating an instance of Engine. However, with IoC, we’ll delegate this responsibility to an external entity.
Implementing IoC Container:
Let’s create a simple IoC container that will be responsible for managing the objects and their dependencies.
Putting it all together:
Now, let’s use our IoC container to manage the Car and Engine instances:
In this example, the Main class acts as the composition root. It creates an instance of the IoCContainer, registers the Engine and Car instances, and resolves the Car instance from the container. The IoC container is responsible for managing the dependencies, and the Car class no longer needs to be concerned with creating its own dependencies.
This is a basic example to illustrate IoC without relying on a specific framework like Spring. In real-world applications, more sophisticated IoC containers or dependency injection frameworks are often used to handle the complexities of object creation and management.
