Class: Design Pattern — Observer

The Observer (publish-subscribe) design pattern with interface + concrete implementations.

class-design-pattern-observer.mmd

classDiagram
  class Subject {
    <<interface>>
    +attach(Observer) void
    +detach(Observer) void
    +notify() void
  }
  class Observer {
    <<interface>>
    +update() void
  }
  class EventEmitter {
    -List~Observer~ observers
    +attach(Observer) void
    +detach(Observer) void
    +notify() void
  }
  class Logger {
    +update() void
  }
  class Alerter {
    +update() void
  }
  Subject <|.. EventEmitter
  Observer <|.. Logger
  Observer <|.. Alerter
  EventEmitter --> Observer

Output

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