@startuml
package com.iluwatar.promise {
  class App {
    - DEFAULT_URL : String {static}
    - LOGGER : Logger {static}
    - executor : ExecutorService
    - stopLatch : CountDownLatch
    - App()
    - calculateLineCount()
    - calculateLowestFrequencyChar()
    - characterFrequency() : Promise<Map<Character, Integer>>
    - countLines() : Promise<Integer>
    - download(urlString : String) : Promise<String>
    - lowestFrequencyChar() : Promise<Character>
    + main(args : String[]) {static}
    - promiseUsage()
    - stop()
    - taskCompleted()
  }
  class Promise<T> {
    - exceptionHandler : Consumer<? super Throwable>
    - fulfillmentAction : Runnable
    + Promise<T>()
    + fulfill(value : T)
    + fulfillExceptionally(exception : Exception)
    + fulfillInAsync(task : Callable<T>, executor : Executor) : Promise<T>
    - handleException(exception : Exception)
    + onError(exceptionHandler : Consumer<? super Throwable>) : Promise<T>
    - postFulfillment()
    + thenAccept(action : Consumer<? super T>) : Promise<Void>
    + thenApply(func : Function<? super T, V>) : Promise<V>
  }
  -class ConsumeAction {
    - action : Consumer<? super T>
    - dest : Promise<Void>
    - src : Promise<T>
    - ConsumeAction(src : Promise<T>, dest : Promise<T>, action : Consumer<T>)
    + run()
  }
  -class TransformAction<V> {
    - dest : Promise<V>
    - func : Function<? super T, V>
    - src : Promise<T>
    - TransformAction<V>(src : Promise<T>, dest : Promise<T>, func : Function<T, R>)
    + run()
  }
  ~class PromiseSupport<T> {
    - COMPLETED : int {static}
    - FAILED : int {static}
    - RUNNING : int {static}
    - exception : Exception
    - lock : Object
    - state : int
    - value : T
    ~ PromiseSupport<T>()
    + cancel(mayInterruptIfRunning : boolean) : boolean
    ~ fulfill(value : T)
    ~ fulfillExceptionally(exception : Exception)
    + get() : T
    + get(timeout : long, unit : TimeUnit) : T
    + isCancelled() : boolean
    + isDone() : boolean
  }
  class Utility {
    - LOGGER : Logger {static}
    + Utility()
    + characterFrequency(fileLocation : String) : Map<Character, Integer> {static}
    + countLines(fileLocation : String) : Integer {static}
    + downloadFile(urlString : String) : String {static}
    + lowestFrequencyChar(charFrequency : Map<Character, Integer>) : Character {static}
  }
}
TransformAction -->  "-src" Promise
TransformAction --+ Promise
ConsumeAction -->  "-src" Promise
ConsumeAction --+ Promise
Promise --|> PromiseSupport 
@enduml