Dependency Injection

Dependency Injection:

• DI is a technique where 1object (or static method) supplies dependencies for other objects.i.e. Passing the service to the client, rather than client building the service himself.
• It is done so that your code can be re-used and can be loosely coupled.

Why to Use Dependency Injection ??

           The intent behind the DI is to de-couple objects to an object to an extent, such that no other client code had to be changed simply because object needs to be changed to diff. one

Advantages:

• DI allows concurrent or Independent development
• Decrease coupling between the class & dependency

There are 3 types in which DI can be achieved:

1.      Constructor Injection: Dependencies are provided through class Constructor.

2.      Setter Injection: Client exposes the setter method() ,  so that the injector injects the dependencies

3.      Interface Injection: Client must implement that expose the setter() that accept dependency

Constructor Injection :

Public class Client {

                              // Constructor

                              Client(Service service){

                              This.service= service;

}

}

Setter Injection :

      Public class Client {

                              public void serService(Service service){

                              This.service= service;

}

     }

Interface Injection :

      Public interface Client {

                             

                              Public void setService(Service service);

     }

Steps to Design DI: 

1.      Design interfaces

2.      Don’t use classes to call other class, instead use dependencies

3.      Don’t create objects, set it NULL

4.      Move objects to the class level

5.      Create Getters & Setters

Eg:

Public interface test {    // 1

        Void add(int I, int j);

}

Public class TestClass implements test {

        Test obj= new test(); // Do not do this, instead follow next step

        Test obj= null // 3

Public static void main(String [] args)

{

        Int sum= obj.add(1,2);

        System.out.println(sum);

}

 //Getter & Setters //5

}