State Machine Design Pattern

• It is used when applicability of each operation depends on the state of the system
• We create an interface for State with all the possible operations
• All the states implement the interface and in case of unsupported operations:
  • Provide default implementation
  • Throw exception
• Uses:
  • Vending Machine

classDiagram

class State {
    <<interface>>
    +operation1()
    +operation2()
}

class State1 {
    +operation1()
    +operation2()
}

class State2 {
    +operation1()
    +operation2()
}

State <|-- State1
State <|-- State2