ValidNumber.kt

class StateContext {
    private var state: State? = null

    fun setState(state: State?){
        this.state = state
    }

    public fun parseString(number: String): Boolean{
        setState(InitialState())
        for(character in number){
            parseCharacter(character)
        }
        return state?.final == true
    }

    private fun parseCharacter(character: Char){
        state?.parseCharacter(this, character)
    }
}