UML state diagram

One 、 State diagram

        A class defines an abstraction of a set of objects , Each object is an instance of a class , But for an object , It has a series of States throughout its life cycle . State describes the dynamic life cycle of an object .

   “ people ” It's a class , and “ you ”、“ I ”、“ Zhang San ” Are all “ people ” An instance of this class ,“ stand ”、“ lying ” Wait is a state of the object .

        Throughout the life cycle of an object , Its state will change , The state machine is used to represent the state changes and the response to events of an object in its life cycle .

Two 、 Constituent elements 、 State machine

A state machine is a partial view of an object 、 A view that separates an object from its external world and examines its behavior independently . State machines are a good way to accurately describe behavior .

For example, describe the detailed behavior of the water heater when it works ：

state ： It means that certain conditions are met in the object life cycle 、 A condition or condition that performs certain activities or waits for certain events .

Start state

End state

  Naming status  

       In a state machine diagram , There are no more than two core elements ： One is the state represented by rounded rectangles ; The other is between States 、 A directional arrow line containing some text descriptions , These arrows become transformation .

       A transition is a relationship between two states , Indicates that the object will perform certain actions in the first state , And enter the second state when a specific event occurs and the conditions are met .

3、 ... and 、 How to draw a state diagram

The ideal step to draw a state diagram ： Look for the main state 、 Determine the transition between States , Refine the activities and transitions within the state , Expand details with composite States

1、 Main status of search

When drawing the state machine diagram , The most important activity is to find out the main state . For flight reservation system , Obviously, the states included mainly include ：

a、 When determining the flight plan , Obviously, there is no reservation , And it will be in this situation before someone makes a reservation “ No reservation ” state

b、 For reservation , Obviously there is “ Partial reservation ” and “ Booked ” Two kinds of state

c、 When the flight is about to take off , Obviously “ Reservation closed ”

summary ： There are four states ： No reservation 、 Partial reservation 、 The reservation is completed and closed

2、 Determine the relationship between States

After determining the main state, analyze the transition between States , Draw the corresponding state machine diagram