What Is IoC (Inversion of Control) Principle? A Basic Guide In 2021


This article will find out about what is IoC and how to execute it. This is the initial move towards accomplishing a loosely coupled design, as shown by the accompanying figure:

Tightly Coupled Classes

Implement IoC Using Factory Pattern

Implement DIP by Creating Abstraction

Implement DI

User IoC Container

Loosely Coupled Classes

  1. What is IoC?
  2. What is IoC in spring? 
  3. What is IoC container? 
  4. What is a spring IoC container? 
  5. Implementation Techniques
  6. Difference between Dependency Injection and Service Locator

1. What is IoC?

IoC is a design principle (albeit a few groups related to it as an IoC design pattern). As the name recommends, it is utilized to modify various types of controls in object-oriented design to accomplish the loose coupling. Here, controls attribute to any extra responsibilities a class has, other than its fundamental responsibilities. 

IoC incorporates control over the progression of an application and control over the progression of item creation or dependent object binding and creation.

2. What is IoC in spring? 

Spring IoC is the mechanism to accomplish loose coupling between Objects conditions. To accomplish loose coupling and dynamic restricting of the items at runtime, objects conditions are infused by other assembler objects.

3. What is IoC container? 

The IoC container is dependable to assemble, configure and instantiate the objects. The IoC container gets information from the extensible mark-up language file and works in a like manner.

4. What is a spring IoC container? 

The Spring container is at the centre of the Spring Framework. The spring container will make the objects, wire them together, configure them, and deal with their total life cycle from creation till destruction.

 Business Objects POJOs

                                      Configuration Metadata →     The Spring Container

                  ↓       Final Result

 Fully Configured System

   Ready for Use

5. Implementation Techniques

IoC can be executed in different programs. A few fundamental design patterns are utilized to execute IoC in object-oriented programming.

  1. Utilizing the methodology design pattern.
  2. Utilizing the template technique design pattern.
  3. Utilizing a contextualized lookup.
  4. Utilizing the dependency injection pattern.
  5. Utilizing a service locator pattern.


  • Inversion of Control Example:

To comprehend the IoC and its implementation by utilizing the service locator pattern and dependency injection, we take an example, a basic one. One illustration of such a situation and such a dependency is the point at which a class, shown as A below, utilizes another class, B.

A → B

The purchaser, A, needs the consumed class, B, to achieve something. That is all acceptable and characteristic, yet does A need to realize that it utilizes B? 

Isn’t it enough that A realizes that it utilizes something that has the behaviour, the strategies, properties and so on of B without realizing who actualizes the behaviour? 

By removing a theoretical meaning of the behaviour utilized by A in B, represented as Z below, and letting customer A utilize an occasion of that rather than B, it can keep on doing what it manages without knowing the particulars about B.

A → Interface (Z)


In the diagram above, B implements Z, and A uses an occurrence of Z. While it’s very conceivable that A actually utilizes B’s fascinating that A doesn’t realize that. It simply realizes that it utilizes something that implements Z.

  • Dependency Injection (aka D. I.)

DI is a design pattern utilised to actualize Inversion of Control. It permits the formation of dependent objects outside of a class and gives those objects to a class unexpectedly. Utilizing Dependency Injection, we move the creation and restricting of the dependent objects outside of the class that relies upon them.

The DI pattern includes three sorts of classes. 

  1. Client Class
  2. Service Class
  3. Injector Class


Client → Service

                                                  ↑     ↑


                                                                                        (Dependency Injection)

  • Service Locator (aka SL)

The SL pattern is a design pattern utilized in software improvement to embody the cycles engaged with getting assistance with a powerful reflection layer. This pattern utilizes a central registry known as the “Service Locator or SL”, which on-demand restores the data important to play out a specific task.

6. Difference between Dependency Injection and Service Locator

The Dependency Injection or DI is given to the target object without the object doing anything. In other words, the Dependency Injection or DI is injected into the target object, while Service Locator or SL the target object, access its services from a locator (register, container, and so on), which assists with looking for the Dependency Injection or DI request and give them to the target object. It isn’t injected, however, located, all things considered.

The difference between Inversion of Control and Dependency Injection is that in Inversion of Control in a design worldview to give more control to the focused-on segments of your application, the ones completing the work. At the same time, Dependency injection is a pattern utilised to make cases of objects that different objects depend on upon without knowing at an incorporate time which class will be utilized to give that usefulness.

The difference between IoC and Dependency Injection is that the two ideas cooperate in this manner to consider significantly more reusable, flexible, and embodied code to be composed.


IoC conventional programming, the progression of the business rationale is dictated by objects that are statically appointed to each other.

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