状态模式——详解红绿灯问题

小鱼儿 2022-06-13 12:24 232阅读 0赞

# 状态模式——详解红绿灯问题 #

状态模式的定义是这样的：

允许对象在内部状态改变时改变它的行为，对象看起来好像修改了它的类。

下面做一个简答的解释，就是说当对象的状态改变了之后，再次调用对象的方法，对象会提供不同的动作。下面是一个例子：

![Center][]

这个是一个红绿灯问题（为了解释状态模式）。面前有一盏灯和3个按钮，灯在不同状态下按不同的灯，会给出当前转换到某种灯的状态，同时灯的颜色会发生变化。

好，下面是这个问题的解决方案：

![Center 1][]

下面是具体实现：

IState.java

package com.xueyou.demo.service;
    
    public interface IState {
        public void buttonAPress();
    
        public void buttonBPress();
    
        public void buttonCPress();
    }

StateBlack.java

package com.xueyou.demo.serviceimpl;
    
    import com.xueyou.demo.Singnal;
    import com.xueyou.demo.service.IState;
    
    public class StateBlack implements IState{
        private Singnal singnal;
    
        public StateBlack(Singnal singnal) {
            this.singnal = singnal;
        }
    
        @Override
        public void buttonAPress() {
            System.out.println("turn to yellow");
            
        }
    
        @Override
        public void buttonBPress() {
            System.out.println("turn to close");
            singnal.setState(singnal.getStateEnd());
        }
    
        @Override
        public void buttonCPress() {
        }
    }

StateEnd.java

package com.xueyou.demo.serviceimpl;
    
    import com.xueyou.demo.Singnal;
    import com.xueyou.demo.service.IState;
    
    public class StateEnd implements IState {
        private Singnal singnal;
    
        public StateEnd(Singnal singnal) {
            this.singnal = singnal;
        }
    
        @Override
        public void buttonAPress() {
    
        }
    
        @Override
        public void buttonBPress() {
    
        }
    
        @Override
        public void buttonCPress() {
    
        }
    }

StateGreen.java

package com.xueyou.demo.serviceimpl;
    
    import com.xueyou.demo.Singnal;
    import com.xueyou.demo.service.IState;
    
    public class StateGreen implements IState{
        private Singnal singnal;
    
        public StateGreen(Singnal singnal) {
            this.singnal = singnal;
        }
    
        @Override
        public void buttonAPress() {
            System.out.println("turn to yellow");
            singnal.setState(singnal.getStateYellow());
        }
    
        @Override
        public void buttonBPress() {
        }
    
        @Override
        public void buttonCPress() {
            System.out.println("turn to red");
            singnal.setState(singnal.getStateRed());
        }
    }

StateRed.java

package com.xueyou.demo.serviceimpl;
    
    import com.xueyou.demo.Singnal;
    import com.xueyou.demo.service.IState;
    
    public class StateRed implements IState{
        private Singnal singnal;
    
        public StateRed(Singnal singnal) {
            this.singnal = singnal;
        }
    
        @Override
        public void buttonAPress() {
            System.out.println("turn to green");
            singnal.setState(singnal.getStateGreen());
        }
    
        @Override
        public void buttonBPress() {
        }
    
        @Override
        public void buttonCPress() {
            System.out.println("turn to yellow");
            singnal.setState(singnal.getStateYellow());
        }
    }

StateStart.java

package com.xueyou.demo.serviceimpl;
    
    import com.xueyou.demo.Singnal;
    import com.xueyou.demo.service.IState;
    
    public class StateStart implements IState {
        private Singnal singnal;
    
        public StateStart(Singnal singnal) {
            this.singnal = singnal;
        }
    
        @Override
        public void buttonAPress() {
            System.out.println("turn to black");
            singnal.setState(singnal.getStateBlack());
        }
    
        @Override
        public void buttonBPress() {
        }
    
        @Override
        public void buttonCPress() {
    
        }
    }

StateYellow.java

package com.xueyou.demo.serviceimpl;
    
    import com.xueyou.demo.Singnal;
    import com.xueyou.demo.service.IState;
    
    public class StateYellow implements IState {
        private Singnal singnal;
    
        public StateYellow(Singnal singnal) {
            this.singnal = singnal;
        }
    
        @Override
        public void buttonAPress() {
            System.out.println("turn to red");
            singnal.setState(singnal.getStateRed());
        }
    
        @Override
        public void buttonBPress() {
            System.out.println("turn to black");
            singnal.setState(singnal.getStateBlack());
        }
    
        @Override
        public void buttonCPress() {
            System.out.println("turn to green");
            singnal.setState(singnal.getStateGreen());
        }
    }

package com.xueyou.demo;
    
    import com.xueyou.demo.service.IState;
    import com.xueyou.demo.serviceimpl.*;
    
    import java.util.HashMap;
    import java.util.Map;
    
    
    public class Singnal {
    
        private IState stateStart;
        private IState stateEnd;
        private IState stateBlack;
        private IState stateYellow;
        private IState stateRed;
        private IState stateGreen;
    
    
        private IState state = stateStart;
        private Map<String, String> stateMap = new HashMap<>();
    
        public IState getStateStart() {
            return stateStart;
        }
    
        public IState getStateEnd() {
            return stateEnd;
        }
    
        public IState getStateBlack() {
            return stateBlack;
        }
    
        public IState getStateYellow() {
            return stateYellow;
        }
    
        public IState getStateRed() {
            return stateRed;
        }
    
        public IState getStateGreen() {
            return stateGreen;
        }
    
        public IState getState() {
            return state;
        }
    
        public void setState(IState state) {
            this.state = state;
        }
    
        public Singnal() {
            stateStart = new StateStart(this);
            stateEnd = new StateEnd(this);
            stateBlack = new StateBlack(this);
            stateYellow = new StateYellow(this);
            stateRed = new StateRed(this);
            stateGreen = new StateGreen(this);
            this.state = stateStart;
            stateMap.put("StateStart", "Start");
            stateMap.put("StateYellow", "Yellow");
            stateMap.put("StateBlack", "Black");
            stateMap.put("StateRed", "Red");
            stateMap.put("StateGreen", "Green");
            stateMap.put("StateEnd", "End");
        }
    
        public Singnal buttonAPress() {
            state.buttonAPress();
            return this;
        }
    
        public Singnal buttonBPress() {
            state.buttonBPress();
            return this;
        }
    
        public Singnal buttonCPress() {
            state.buttonCPress();
            return this;
        }
    
        public Singnal showState() {
            System.out.println("now state is : " + stateMap.get(this.state.getClass().getSimpleName()));
            return this;
        }
    }

App.java

package com.xueyou.demo;
    
    /**
     * Hello world!
     */
    public class App {
        public static void main(String[] args) {
            Singnal singnal = new Singnal();
            singnal.showState().buttonAPress().showState().buttonAPress()
                    .showState().buttonAPress().showState().buttonAPress()
                    .showState().buttonAPress().showState().buttonBPress()
                    .showState().buttonBPress().showState();
        }
    }

运行结果：

![Center 2][]

[Center]: /images/20220613/a9bd6f0097d946a6b65f0e6dec2a0147.png
[Center 1]: /images/20220613/b41ac36071f24ccb90d0232c61ea8988.png
[Center 2]: /images/20220613/83d75b1bf08a4f92b17faa874ef74af8.png