一、简介
状态模式一般用来实现状态机，而状态机常用在游戏、工作流引擎等系统开发中。不过，状态机的实现方式有多种，除了状态模式，比较常用的还有分支逻辑法和查表法。该模式允许对象内部状态改变使改变它的行为。
二、适用场景
- 行为随状态而改变
- 条件、分支语句的替代者
三、UML类图
四、案例
交通信号灯的红黄绿三色的变化。
go
package main
import (
"fmt"
)
type TrafficLightState interface {
Handle(trafficLight *TrafficLight)
}
type RedState struct {
Name string
}
func NewRedState() *RedState {
return &RedState{Name: "Red"}
}
func (r *RedState) Handle(trafficLight *TrafficLight) {
fmt.Println("Red light: Stopped")
trafficLight.SetState(NewGreenState())
}
type YellowState struct {
Name string
}
func NewYellowState() *YellowState {
return &YellowState{Name: "Yellow"}
}
func (y *YellowState) Handle(trafficLight *TrafficLight) {
fmt.Println("Yellow light: Be prepared to stop")
trafficLight.SetState(NewRedState())
}
type GreenState struct {
Name string
}
func NewGreenState() *GreenState {
return &GreenState{Name: "Green"}
}
func (g *GreenState) Handle(trafficLight *TrafficLight) {
fmt.Println("Green light: Go")
trafficLight.SetState(NewYellowState())
}
type TrafficLight struct {
State TrafficLightState
}
func NewTrafficLight() *TrafficLight {
return &TrafficLight{State: NewRedState()}
}
func (t *TrafficLight) SetState(state TrafficLightState) {
t.State = state
}
func (t *TrafficLight) Change() {
t.State.Handle(t)
}
func main() {
trafficLight := NewTrafficLight()
for i := 0; i < 10; i++ {
trafficLight.Change()
}
}