what

什么是有限状态机

把业务模型抽象成一个有限状态机状态机四要素：现态、次态、条件、动作三特征：

很多业务其实也能套用状态模式，什么情况该用状态模式？

State: each State has incoming Transitions and outgoing Transitions.
When {@link State#mBranchStart} is true, all the outgoing Transitions may be triggered, when
{@link State#mBranchStart} is false, only first outgoing Transition will be triggered.
When {@link State#mBranchEnd} is true, all the incoming Transitions must be triggered for the
State to run. When {@link State#mBranchEnd} is false, only need one incoming Transition triggered
for the State to run.
Transition: three types:
1. Event based transition, transition will be triggered when {@link #fireEvent(Event)} is called.
1. Auto transition, transition will be triggered when {@link Transition#mFromState} is executed.
1. Condiitonal Auto transition, transition will be triggered when {@link Transition#mFromState}
is executed and {@link Transition#mCondition} passes.
@hide */

一个从 A 到 B 的转移，那么他就是 A 的传出转移 B 的传入转移。每个状态各自维护两个传出、传入转移列表

triggered 触发， BranchStart，triggered