Dependency injection is a technique where objects receive their dependencies from external sources rather than creating them themselves. It decouples classes from their dependencies and allows dependencies to be replaced without modifying the dependent class. A dependency injection container creates and maps dependencies, providing them to classes through constructor or property injection according to how they are configured in the container.

1. Dependency injection
What? Where? Why? when?

2. WHAT IS DEPENDENCY?

3. INJECTION
Push dependency from outside into the class.
• Fetch dependency
• Receive dependency

4. DI
Ask third party to create object, instead of create dependencies yourself.

5. WHY NEED DI
Decouple classes construction from construction of your dependency.

6. DEPENDENCY INVERSION PRINCIPLE
Class Dependency
Interface
Implementation
Dependency

7. DI CONTAINER
Create and map dependency

8. DI LIBRARIES FOR ANDROID
• ButterKnife
• Dagger 2