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表驱动法2

继续展示使用表驱动法实现的例子。

 

例子1:

需求:输入一个月份,和一个年份,输出该月的天数。

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public class DaysPerMonth {
 
    private int daysPerMonthLeapYear[] = { 31, 29, 31, 30, 31, 30, 31, 31, 30,
            31, 30, 31 };
    private int daysPerMonthNLeapYear[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30,
            31, 30, 31 };
 
    private final String ErrorHint = "输入参数不符合规定";
 
    public boolean isLeapYear(int year) {
        if (year % 4 == 0 && year % 100 != 0) {
            return true;
        }
 
        if (year % 4 == 0 && year % 400 == 0) {
            return true;
        }
 
        return false;
    }
 
    public int getDaysOfPerMonth(int month, int year) throws Exception {
 
        if (!validateParam(month, year)) {
            throw new Exception(ErrorHint);
        }
 
        if (isLeapYear(year)) {
            return daysPerMonthLeapYear[month - 1];
        } else {
            return daysPerMonthNLeapYear[month - 1];
        }
    }
 
    private boolean validateParam(int month, int year) {
 
        if (month <= 0 || month > 12 || year <= 0) {
            return false;
        } else {
            return true;
        }
    }
 
    public static void main(String[] args) {
 
        DaysPerMonth one = new DaysPerMonth();
 
        try {
            System.out.println(one.getDaysOfPerMonth(2, 2000));
        } catch (Exception e) {
 
            e.printStackTrace();
        }
 
    }
}

使用表驱动法和不使用,效果的是明显的。不使用,又将会是一大堆的if(month == 1) 输出31之类的。可以看出,表驱动法,实现上述的需求过程中,也是将逻辑判断简化为查表操作。

 

例子2:

需求:输入是年龄,性别,婚姻状况,是否吸烟,然后,按照给定的规则,得到相应的费率。

为了简单起见,假设有以下组合:

1.男,已婚,吸烟,年龄。

2.女,已婚,不吸烟,年龄。

3.男,未婚,吸烟,年龄。

其实,按照上述情况,组合数量是2*2*2*X = 8X,这个X不同年龄对应的费率。

这个如果写成if判断的话,那是不可想象的,那会有很多if。

假设,有以下费率规定:

1.男,已婚,吸烟,年龄(age)

age>=18 25%
age = 19 12%
age = 20 23%
age = 21 20%
age >=22 30%

 

2.女,已婚,不吸烟,年龄

age>=18 22%
age=19 12%
age=20 2%
age=21 23%
age >=22 21%

 

一个简单的思路是,上述三个组合中,每个组合对应一张表;确定了是哪张表之后,再使用年龄作为索引,在这张表里面查询对应的值。

但是,这里有个问题,从输入的因素:性别,婚姻状况,吸烟否,要从这三个输入因素中确定出对应的表,这里要使用多个if逻辑判断。我想尽力避免这种情况,通过一个转换函数,

该函数的功能是根据这三个输入因素,确定出类型,然后根据该类型找对应的表,这里面再次用到了表驱动方法。

实现:

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public class RateTable {
 
    public static class Gender {
 
        public static String Feamle = "0";
        public static String Male = "1";
    }
 
    public static class MaritalStatus {
 
        public static String Single = "0";
        public static String Married = "1";
    }
 
    public static class SmokingStatus {
 
        public static String Smoking = "0";
        public static String NonSomking = "1";
    }
 
    private HashMap<Integer, Float> typeOne = new HashMap<Integer, Float>();
    private HashMap<Integer, Float> typeTwo = new HashMap<Integer, Float>();
    private HashMap<Integer, Float> typeThree = new HashMap<Integer, Float>();
 
    private HashMap<String, HashMap<Integer, Float>> typeTable = new HashMap<String, HashMap<Integer, Float>>();
 
    public static final int FloorBoundary = 18;
    public static final int UpperBoundary = 22;
 
    public RateTable() {
        initalRateTable();
        initalTypeTable();
    }
 
    private void initalRateTable() {
        initalTypeOne();
        initalTypeTwo();
 
    }
 
    private void initalTypeOne() {
        typeOne.put(FloorBoundary, (float) 0.25);
        typeOne.put(19, (float) 0.12);
        typeOne.put(20, (float) 0.23);
        typeOne.put(21, (float) 0.2);
        typeOne.put(UpperBoundary, (float) 0.3);
 
    }
 
    private void initalTypeTwo() {
        typeTwo.put(FloorBoundary, (float) 0.22);
        typeTwo.put(19, (float) 0.12);
        typeTwo.put(20, (float) 0.02);
        typeTwo.put(21, (float) 0.23);
        typeTwo.put(UpperBoundary, (float) 0.21);
 
    }
 
    private void initalTypeTable() {
        // 表示的顺序是:性别,婚姻,吸烟
        typeTable.put(
                (Gender.Male + MaritalStatus.Married + SmokingStatus.Smoking),
                typeOne);
        typeTable.put(Gender.Feamle + MaritalStatus.Married
                + SmokingStatus.NonSomking, typeTwo);
 
    }
 
    public float getRate(String Gender, String MarriedStatus,
            String SmokingStatus, int age) throws Exception {
        HashMap<Integer, Float> table = typeTable.get(Gender + MarriedStatus
                + SmokingStatus);
 
        if (table == null) {
            throw new Exception("找不到对应的费率表,请重新输入参数");
        }
        if (age > 0 && age <= 18) {
            return table.get(RateTable.FloorBoundary);
        }
 
        if (age >= 22) {
            return table.get(RateTable.UpperBoundary);
        }
 
        return table.get(age);
    }
 
    public static void main(String[] args) {
 
        RateTable one = new RateTable();
 
        try {
            System.out.println("Male_Married_Smoking_  age 20 , the rate:"
                    + one.getRate(Gender.Male, MaritalStatus.Married,
                            SmokingStatus.Smoking, 20));
 
            System.out.println("Femal_Married_NonSmoking_ age 19, the rate:"
                    + one.getRate(Gender.Feamle, MaritalStatus.Married,
                            SmokingStatus.NonSomking, 19));
 
        } catch (Exception e) {
 
            e.printStackTrace();
        }
 
    }
 
}

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上面,两次用到了表驱动方法。一次是,输入的三种信息组合:性别+婚姻状况+吸烟否,将这三个输入项作为一个Key去查表,查找到目标表;然后,得到了目标表之后,再使用

age作为key查询到对应的费率数值。

同样,还是方便扩展:有多少种类型,就添加多少个HashMap<Integer, Float>,每个代表某种具体类型下的费率表;也方便修改,只要修改某个具体费率表下某个年龄对应的费率便可。

同样,还是减少了多次if的逻辑判断。