使用策略模式和多态去掉if/else、switch

很多时候我们会在代码中使用很笨矬的if/else、switch语句，代码阅读起来相当的吃力。有没有一种方式可以替换呢。今天就让我们看看强大策略模式如何解决这一问题吧。

if/else示例

学生类(student)

package com.zhanghf.noifelse;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * Created by Administrator on 2017/4/9.
 */

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private Achievement achievement;

    /**
     * 获取学生成绩
     *
     * @return 成绩
     */
    public String getAchievement() {
        if (this.achievement == Achievement.A) {
            return "学生成绩为:A";
        } else if (this.achievement == Achievement.B) {
            return "学生成绩为:B";
        } else {
            return "学生成绩为:C";
        }
    }
}

成绩枚举类(Achievement)

package com.zhanghf.noifelse;

/**
 * Created by Administrator on 2017/4/9.
 */
public enum Achievement {
    A,B
}

方法测试类(Application)

package com.zhanghf.noifelse;

/**
 * Created by Administrator on 2017/4/9.
 */
public class Application {

    public static void main(String[] args) {
        Student student = new Student(Achievement.B);
        System.out.println(student.getAchievement());
    }

}

可以看到在getAchievement方法中，使用了很多if/else if /else这样的语句，下面我们先使用策略模式来替换。我们先来看看类结构(UML)。

策略模式.png

成绩接口(Achievement)

package com.zhanghf.noifelse.strategy;

/**
 * Created by Administrator on 2017/4/9.
 */
public interface Achievement {
    String getAchievement();
}

优秀成绩类(ExcellentAchievement)

package com.zhanghf.noifelse.strategy;

/**
 * Created by Administrator on 2017/4/9.
 */
public class ExcellentAchievement implements Achievement {

    public String getAchievement() {
        return "学生成绩为:A";
    }
}

良好成绩类(GoodAchievement)

package com.zhanghf.noifelse.strategy;

/**
 * Created by Administrator on 2017/4/9.
 */
public class GoodAchievement implements Achievement {

    public String getAchievement() {
        return "学生成绩为:B";
    }
}

及格成绩类(AverageAchievement)

package com.zhanghf.noifelse.strategy;

/**
 * Created by Administrator on 2017/4/9.
 */
public class AverageAchievement implements Achievement {

    public String getAchievement() {
        return "学生成绩为:C";
    }
}

学生类(Student)

package com.zhanghf.noifelse.strategy;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * Created by Administrator on 2017/4/9.
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private Achievement achievement;

    public String getAchievement() {
        return this.achievement.getAchievement();
    }
}

代码测试类(Application)

package com.zhanghf.noifelse.strategy;


/**
 * Created by Administrator on 2017/4/9.
 */
public class Application {
    public static void main(String[] args) {
        Student student = new Student(new AverageAchievement());
        System.out.println(student.getAchievement());
    }
}

---

下面使用多态方式:

学生类(student)

package com.zhanghf.noifelse.polymorphic;

import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * Created by Administrator on 2017/4/9.
 */
@Data
@NoArgsConstructor
public class Student {

    public String getAchievement(AverageAchievement averageAchievement) {
        return averageAchievement.getAchievement();
    }

    public String getAchievement(ExcellentAchievement excellentAchievement) {
        return excellentAchievement.getAchievement();
    }

    public String getAchievement(GoodAchievement goodAchievement) {
        return goodAchievement.getAchievement();
    }

}

及格成绩类(AverageAchievement)

package com.zhanghf.noifelse.polymorphic;

/**
 * Created by Administrator on 2017/4/9.
 */
public class AverageAchievement{

    public String getAchievement() {
        return "学生成绩为:C";
    }
}

良好成绩类(GoodAchievement)

package com.zhanghf.noifelse.polymorphic;

/**
 * Created by Administrator on 2017/4/9.
 */
public class GoodAchievement{

    public String getAchievement() {
        return "学生成绩为:B";
    }
}

优秀成绩类(ExcellentAchievement)

package com.zhanghf.noifelse.polymorphic;

/**
 * Created by Administrator on 2017/4/9.
 */
public class ExcellentAchievement {

    public String getAchievement() {
        return "学生成绩为:A";
    }
}

代码测试类(Application)

package com.zhanghf.noifelse.polymorphic;

/**
 * Created by Administrator on 2017/4/9.
 */
public class Application {
    public static void main(String[] args) {
        Student student = new Student();
        AverageAchievement averageAchievement = new AverageAchievement();
        System.out.println(student.getAchievement(averageAchievement));
    }
}