Dependency injection or Inversion of control are the two terms used for same thing. In case of DI, we define the process of instatiating an object into a non java class generally xml file.
Instead of using new word to instatiate any object, reference of an object is retrieved from an config file.
The basic concept of the Inversion of Control pattern (also known as dependency injection) is that you do not create your objects but describe how they should be created. You don't directly connect your components and services together in code but describe which services are needed by which components in a configuration file.
Objects can be injected through setter or constructor. Dependency Injection means we can inject all the dependenciess to ur object in the xml file.
For example in order to establish connection ,Connection object needs datasource object.
So in the xml file first we declare a bean for DataSource ,in that we give parameters for connecting to database like url username passwordetc We delare another bean named Connection in which the above declared datasource object is injected through setter or constructor.
So at the time of startup the container reads the xml file. ann all the required objects are created without the developer explicitly creating objects.
Dependency injection is the ability to inject collobrative objects dynamically.Suppose you want to call a method of particular class, so for that you use new operator help and make object of that class and call the require method using ref. varibale of that class .But when you use Spring dependency injection , you don't have to do all these stuff, instead of that you configure a xml file in which you mention what all objects you require in you class, it will get ready for use. You don't have to create or instantiate .
