@startuml
package com.iluwatar.state {
  class PeacefulState {
    - mammoth : Mammoth
    + PeacefulState(mammoth : Mammoth)
    + observe()
    + onEnterState()
  }
  interface State {
    + observe() {abstract}
    + onEnterState() {abstract}
  }
  class App {
    + App()
    + main(args : String[]) {static}
  }
  class AngryState {
    - mammoth : Mammoth
    + AngryState(mammoth : Mammoth)
    + observe()
    + onEnterState()
  }
  class Mammoth {
    - state : State
    + Mammoth()
    - changeStateTo(newState : State)
    + observe()
    + timePasses()
    + toString() : String
  }
}
AngryState -->  "-mammoth" Mammoth
PeacefulState -->  "-mammoth" Mammoth
Mammoth -->  "-state" State
PeacefulState ..|> State 
AngryState ..|> State 
@enduml