if else 深度优化

一. if else表达式过于复杂

if ((condition1 && condition2 ) || ((condition2 || condition3) && condition4)) {
}

问题解决：分解条件表达式，分解成多个独立的函数，为分解的新函进行良好的命名，从而更清楚表达本身意图。

if (date.before(SUMMER_START) || date.after(SUMMER_END)) {
    
}

// 优化后
if (notSummer(date)) {
    
}

二. if else 嵌套过深

public void workOrRest {
    if (isWorkDay()) {
        System.out.println("sad,is work day!!!");
    } else {
        if (isWorkTime()) {
            System.out.println("shit,is work time!!!");
        } else {
            rest();
            System.out.println("happy happy happy!!!");
        }
    }
}

解决办法：经过卫语句，有时候条件式可能出如今嵌套n次才能真正执行，其余分支只是简单报错返回的状况，对于这种状况，应该单独检查报错返回的分支，当条件为真时当即返回，这样的单独检查就是卫语句（guard clauses).卫语句能够把咱们的视线从异常处理中解放出来，集中精力到正常处理的代码中。

public void workOrRest {
    if (isWorkDay()) {
        System.out.println("sad,is work day!!!");
        return;
    }
    
    if (isWorkTime()) {
        System.out.println("shit,is work time!!!");
        return;
    }
    
    rest();
    System.out.println("happy happy happy!!!");
}

三. if else过多

if (houseName.equals("Targaryen")) {
    ...
    System.out.println("Blood and fire");
} else if (houseName.equals("Baratheon")) {
    ...
    System.out.println("Ours is the Fury");
} else if (houseName.equals("Stark")) {
    ...
    System.out.println("Winter is coming");
} else if (houseName.equals("Lannister")) {
    ...
    System.out.println("Hear Me Roar");
} else if (houseName.equals("Arryn")) {
    ...
    System.out.println("as High as Honor");
} else if (houseName.equals("Tyrell")) {
    ...
    System.out.println("Growing Strong");
} else if (houseName.equals("Tully")) {
    ...
    System.out.println("Family, Duty, Honor");
} else if (houseName.equals("Martell")) {
    ...
    System.out.println("Unbent, Unbowed, Unbroken");
} else if (houseName.equals("Greyjoy")) {
    ...
    System.out.println("We Do Not Sow");
} else {
    ...
    System.out.println("world peace");
}

问题解决：利用策略or状态模式，消除业务判断，各之类分别关注本身的实现，大大下降了系统各部分之间的依赖。利用Map缓存分支状态信息。基本能够达到对修改封闭，对扩展开放。

<property name="thronesMap">
            <map>
                <entry key="Targaryen"><bean class="game.of.thrones.TargaryenStrategy"/></entry>
                <entry key="Baratheon"><bean class="game.of.thrones.BaratheonStrategy"/></entry>
                <entry key="Stark"><bean class="game.of.thrones.StarkStrategy"/></entry>
                <entry key="Lannister"><bean class="game.of.thrones.LannisterStrategy"/></entry>
                <entry key="Arryn"><bean class="game.of.thrones.ArrynStrategy"/></entry>
                <entry key="Tyrell"><bean class="game.of.thrones.TyrellStrategy"/></entry>
                <entry key="Tully"><bean class="game.of.thrones.TullyStrategy"/></entry>
                <entry key="Martell"><bean class="game.of.thrones.MartellStrategy"/></entry>
                <entry key="Greyjoy"><bean class="game.of.thrones.GreyjoyStrategy"/></entry>
                <entry key="Default"><bean class="game.of.thrones.DefaultStrategy"/></entry>
            </map>
</property>


public interface GameOfThronesStrategyService {
    /**
    * 具体实现处理
    */
    void mainTitle();
}

thronesMap.get(houseName).mainTitle();