Idle --- off hook event ---> Dialing Dialing --- valid number event ---> Connecting Dialing --- invalid/wrong number event---> Disconnected Connecting --- timeout event---> TimeOut Connecting --- called phone answers event---> Connected Ringing --- called phone answers event---> Connected Connected --- on hook event---> Idle Connected --- line busy event---> Busy Tone Connected --- timeout event-- Connected --- timeout event---> Disconnected Connected --- Play Message event---> Ringing，然后将这个在plantUML以代码的形式描绘出电话线路图状态

好的，以下是代码形式的电话线路图状态：

@startuml
title Telephone State Diagram

[*] --> Idle : Initial State

Idle --> Dialing : Off Hook Event
Dialing --> Connecting : Valid Number Event
Dialing --> Disconnected : Invalid/Wrong Number Event
Connecting --> TimeOut : Timeout Event
Connecting --> Connected : Called Phone Answers Event
Ringing --> Connected : Called Phone Answers Event
Connected --> Idle : On Hook Event
Connected --> Busy Tone : Line Busy Event
Connected --> TimeOut : Timeout Event
Connected --> Disconnected : Timeout Event
Connected --> Ringing : Play Message Event

@enduml

解释一下：

- 初始状态为空闲状态（`[*] --> Idle : Initial State`）。
- 当电话机摘机时，电话状态从空闲状态转入拨号状态（`Idle --> Dialing : Off Hook Event`）。
- 当拨号有效号码时，电话状态从拨号状态转入连接状态（`Dialing --> Connecting : Valid Number Event`）。
- 当拨号号码无效或错误时，电话状态从拨号状态转入未连接状态（`Dialing --> Disconnected : Invalid/Wrong Number Event`）。
- 当连接超时时，电话连接状态从连接状态转入超时状态（`Connecting --> TimeOut : Timeout Event`）。
- 当被拨打的电话接听时，电话连接状态从连接状态或响铃状态转入已连接状态（`Connecting --> Connected : Called Phone Answers Event` 或 `Ringing --> Connected : Called Phone Answers Event`）。
- 当已连接状态的电话机挂机时，电话状态从已连接状态转入空闲状态（`Connected --> Idle : On Hook Event`）。
- 当已连接状态的电话线路忙碌时，电话状态从已连接状态转入忙音状态（`Connected --> Busy Tone : Line Busy Event`）。
- 当已连接状态的电话连接超时时，电话状态从已连接状态转入未连接状态（`Connected --> TimeOut : Timeout Event`）。
- 当已连接状态的电话播放信息时，电话状态从已连接状态转入响铃状态（`Connected --> Ringing : Play Message Event`）。