@startuml
package com.iluwatar.callback {
  interface Callback {
    + call() {abstract}
  }
  abstract class Task {
    + Task()
    + execute() {abstract}
    + executeWith(callback : Callback)
  }
  class App {
    + App()
    + main(args : String[]) {static}
  }
  class SimpleTask {
    + SimpleTask()
    + execute()
  }
  class LambdasApp {
    + LambdasApp()
    + main(args : String[]) {static}
  }
}
SimpleTask --|> Task 
@enduml