Design Problems

• Creating Objects
  • How can a class be independent of how the objects it requires are created?
  • How can a class accept the objects it requires (from an injector object)
    instead of creating the objects directly?
• Specifying Different Configurations
  • How can the way objects are created (the mapping of interfaces to implementations) be specified in separate configuration files or objects?
  • How can an application support different configurations?
• Resolving Dependencies Recursively
  • How can the objects a class requires be created recursively?

Refactoring Problems

• Inflexible Code
  • How can instantiating concrete classes throughout an application (compile-time implementation dependencies) be refactored?
  • How can object creation that is distributed across an application
    be centralized and externalized?

Testing Problems

• Unit Testing
  • How can the objects a class requires be replaced with mock objects
    so that the class can be unit tested in isolation?