Definition for Docker and Dependence Injection.

Simply saying, docker is a tool that lets you package your application along with everything needed to run it. (Can't say it's a perfect analogy but let me try to explain the concept with this example).

 

Suppose you're going to your friend and taking your cell phone with you. Yet your phone's battery is dead and you don't know if your friend would have the same charger as yours so  you pack your phone and charger in a bag to take it so you can use it there as well. The same is the case with docker. Phone is your application, the charger is the dependency for your application to run, the bag is the container and you yourself is docker packagaing the application along with its requiremnts in a container and now you'll be able to use it as you like. Now let me restate the formal definition of docker. It is a tool that allows you to pack your application with all its dependencies in a container and then you can create, deploy or run your application at any platform seamlessly. (hope it makes sense now).

 

Now let's talk about Dependency Injection. Sometimes an object needs other objects for itself. Dependency injection means that the main object does not need to worry about creating those objects at compile time instead say as if you're directly providing the needed objects to main object.

 

Example again. consider a Car object. A Car depends on wheels, engine, fuel, battery, etc. to run. Now each time we're creating a car we need to create instances of all these objects (wheel, battery etc.) as well. Something like. 

 But with dependency injection, we can inject the declaration of these objects into car. as: 

Now car object does not depend on wheel and battery objects to be created before neither does it need to worry about creating them but each time car is created it will be provided with the needed objects. 

Hope this helps and let me know if you still have any confusion.