设计模式之状态设计模式

一、浩言

人静而后安，安而能后定，定而能后慧，慧而能后悟，悟而能后得。

二、背景

开年，看了看最近网上传的《阿里巴巴Java开发规范》,然后看到了如下一部分。

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这里说如果if else if else超过了三层就需要使用状态设计模式。碰巧年前我写了一个订单状态转换的代码，我没有使用if else if else的形式，我使用了case，如果改为if等 就是if else if else形式了。

code.png

所以我就在思考，这段代码是否可以改为所说的状态设计模式了?

三、状态设计模式

3.1状态模式定义：
状态模式是属于行为模式的范畴，即是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。
下图是截取《Head First 设计模式》中的图片

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package com.mouse.design.state;
/**
 * Created by wuhao on 2017/2/7.
 */
public interface State {

    public void insertQuarter();

    public void ejectQuarter();

    public void turnCrank();

    public void dispense();
}

package com.mouse.design.state;
/**
 * Created by wuhao on 2017/2/7.
 */
public class GumballMachine {
    State hasQuarterState;
    State noQuarterState;
    State soldOutState;
    State soldState;
    State winnerState;
    State state = soldOutState;
    int count = 0;
    public GumballMachine(int numberCount) {
        this.count = numberCount;
        hasQuarterState = new HasQuarterState(this);
        noQuarterState = new NoQuarterState(this);
        soldOutState = new SoldOutState(this);
        soldState = new SoldState(this);
        winnerState = new WinnerState(this);
        if (numberCount > 0) {
            state = noQuarterState;
        }
    }
    /**
     * 投币
     */
    public void insertQuarter() {
        state.insertQuarter();
    }
    /**
     * 退还硬币
     */
    public void ejectQuarter() {
        state.ejectQuarter();
    }
    /**
     * 转动转轴
     */
    public void turnCrank() {
        state.turnCrank();
        state.dispense();
    }
    void setState(State state) {
        this.state = state;
    }
    /**
     * 释放糖果并且糖果数减1;
     */
    void releaseBall() {
        System.out.println("a gumball comes rolling  out the slot");
        if (count != 0) {
            count = count - 1;
        }
    }
    public State getHasQuarterState() {
        return hasQuarterState;
    }
    public void setHasQuarterState(State hasQuarterState) {
        this.hasQuarterState = hasQuarterState;
    }
    public State getNoQuarterState() {
        return noQuarterState;
    }
    public void setNoQuarterState(State noQuarterState) {
        this.noQuarterState = noQuarterState;
    }
    public State getSoldOutState() {
        return soldOutState;
    }
    public void setSoldOutState(State soldOutState) {
        this.soldOutState = soldOutState;
    }
    public State getSoldState() {
        return soldState;
    }
    public void setSoldState(State soldState) {
        this.soldState = soldState;
    }
    public State getWinnerState() {
        return winnerState;
    }
    public void setWinnerState(State winnerState) {
        this.winnerState = winnerState;
    }
    public State getState() {
        return state;
    }
    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }
}

HasQuarterState类

package com.mouse.design.state;
import java.util.Random;
/**
 * Created by wuhao on 2017/2/7.
 */
public class HasQuarterState implements State {

    GumballMachine gumballMachine;

    public HasQuarterState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("你不能重复投币");
    }

    @Override
    public void ejectQuarter() {
        System.out.println("退还投入的硬币！！！");
        gumballMachine.setState(gumballMachine.getNoQuarterState());
    }

    @Override
    public void turnCrank() {
        System.out.println("you turn...");
        int win = new Random().nextInt(10);
        System.out.println("win--->"+win);
        if( (0 == win) && gumballMachine.getCount() > 0  ){
            gumballMachine.setState(gumballMachine.getWinnerState());
        }else{
            gumballMachine.setState(gumballMachine.getSoldState());
        }
    }
    @Override
    public void dispense() {
        System.out.println("No gumball dispensed...");
    }
}

client.java类

package com.mouse.design.state;
/**
 * Created by wuhao on 2017/2/7.
 */
public class Client {
    public static void main(String[] args) {
        GumballMachine  gumballMachine = new GumballMachine(5);
        System.out.println("---------1--------");
        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();

        System.out.println("--------2-----");
        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();

        System.out.println("------3-------");
        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();

        System.out.println("------4-------");
        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();

        System.out.println("------5-------");
        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();

        System.out.println("------6-------");
        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();
    }
}

3.3 代码
代码已经上传到github上了，之前一直用bitbucket，不过现在把一些代码弄到github上。
https://github.com/MahoneWu/mouse-java-git.git

四：思考

最近看那个规范，觉得对于我来说还是有很大很大帮助的，其中的一些东西注意项，有说到需要注意的设计模式，比如"模板设计模式"，这篇写的"状态设计模式"，其实设计模式在思维上是很特别的，写法也是。所以状态设计模式一般用于"状态的变化并且业务复杂的"。
近期了把去年没写完的几篇文章陆续发了，还有很早写的两篇比较简单的设计模式的文章。都是简单的记载下了。并且所有的测试代码都会放到github上面了。

五：浩语

                                           __                                                        
                            __  _  ____ __|  |__ _____    ___
                            \ \/ \/ /  |  \  |  \\__  \  /  _ \   
                             \     /|  |  /   Y  \/ __ \(  <_> )
                              \/\_/ |____/|___|  (____  /\____/ 
                                                    \/     \/          
                                 任何事情都是要靠努力和用心。