Design Problems

• Defining Abstraction and Implementation Independently
  • How can an abstraction and its implementation vary independently?
  • How can a compile-time binding between
    an abstraction and its implementation be avoided?
• Exchanging Implementations at Run-Time
  • How can an abstraction be configured with an implementation?
  • How can an implementation be selected and exchanged at run-time?
• Flexible Alternative to Subclassing
  • How can a flexible alternative be provided to subclassing
    for changing an implementation at compile-time?