状态图(Statechart Diagram)是描述一个实体基于事件反应的动态行为，显示了该实体如何根据当前所处的状态对不同的事件做出反应。

mermaid stateDiagram

mermaid关键字stateDiagram或stateDiagram-v2

方向

语法direction TB/BT/RL/LR，默认TB

状态定义

简单状态	stateDiagram-v2 direction LR s1 --> s2
别名	stateDiagram-v2 direction LR state "this is state s1" as s1 s2: this is state s2 s1 --> s2: 连接描述
开始和结束	stateDiagram-v2 direction LR %% [*]在左边表示开始右边表示结束 [*] --> [*]
复合状态	stateDiagram-v2 [*] --> First state First { [*] --> Second state Second { [*] --> second second --> Third state Third { [*] --> third third --> [*] } } }
选择	stateDiagram-v2 %% 关键语法 state if_state <<choice>> [*] --> IsPositive IsPositive --> if_state if_state --> False: if n < 0 if_state --> True : if n >= 0 False --> [*] True --> [*]
fork/join状态	stateDiagram-v2 state fork_state <<fork>> %% fork语法 [*] --> fork_state fork_state --> State2 fork_state --> State3 %% join语法 state join_state <<join>> State2 --> join_state State3 --> join_state join_state --> State4 State4 --> [*]
并发状态	stateDiagram-v2 [*] --> Active state Active { [*] --> NumLockOff NumLockOff --> NumLockOn : EvNumLockPressed NumLockOn --> NumLockOff : EvNumLockPressed -- [*] --> CapsLockOff CapsLockOff --> CapsLockOn : EvCapsLockPressed CapsLockOn --> CapsLockOff : EvCapsLockPressed }
备注	stateDiagram-v2 State1: The state with a note %% 多行备注 note right of State1 Important information! You can write break line notes. end note State1 --> State2 %% 单行备注 note left of State2 : note left

综合示例

以java线程状态为例

stateDiagram-v2 [*] --> Runnable: start() Runnable --> Running: cpu schedule Running --> Runnable: cpu schedule bwp: Blocked in object's wait pool blp: Blocked in object's lock pool Running --> bwp: wait() must have lock bwp --> blp: notify()/interrupt() blp --> Runnable: acquires lock Running --> blp: synchronized Running --> Block: block event Block --> Runnable: block event end Running --> [*]: run() complete