定义
方法的入参过多，或存在不必要的参数
影响
- 方法不易被理解、使用，方法签名容易不稳定，不易维护
改进目标
- 去除多余参数，合并部分参数，提升方法签名稳定性
方法
- 以查询取代参数
- 保持对象完整
- 引入参数对象
- 函数组合成类
- 移除标记参数
案例
代码背景
- 计算某表演项目的票价；
- 只有符合年龄要求才可以购买；
- 儿童票5折，学生可以打9折，二者取最小；
症状/问题
方法入参过多，该问题的具体情况有：
- 某几个入参有关联性
- 某几个入参是一个对象的部分字段
- 某些入参可通过其他入参计算得到
- 函数逻辑都是针对某个入参对象属性的加工
- 某些入参属于标记，用于控制代码逻辑
public class TicketInfo {
private final double baseDiscount;
public TicketInfo(double baseDiscount) {
this.baseDiscount = baseDiscount;
}
/**
* 获取票据信息
*
* @param name 姓名
* @param age 年龄
* @param isChild 是否儿童
* @param isStudent 是否学生
* @param ageFloor 年龄上限
* @param ageCeiling 年龄下限
* @param performance 演出信息
* @param basicPrice 基本票价
* @return 票据信息
*/
public String getTicketInfo(String name, int age, boolean isChild, boolean isStudent, int ageFloor, int ageCeiling,
Performance performance, double basicPrice) {
if ((age < ageFloor || age > ageCeiling)) {
throw new IllegalArgumentException("age is out of valid range, cannot buy ticket!");
}
return getPerformanceInfo(performance)
+ getConsumerInfo(name, age, isStudent, isChild)
+ getPriceInfo(isChild, isStudent, basicPrice);
}
private String getPriceInfo(boolean isChild, boolean isStudent, double basicPrice) {
final double discount = getDiscount(isStudent, isChild);
final double ticketPrice = getTicketPrice(discount, basicPrice);
return "priceInfo" + Constant.LINE_SEPARATOR
+ "\tprice: " + ticketPrice + Constant.LINE_SEPARATOR
+ "\tdiscount: " + discount + Constant.LINE_SEPARATOR;
}
private double getDiscount(boolean isStudent, boolean isChild) {
double childDiscount = calculateDiscount("Child", isChild, isStudent);
double studentDiscount = calculateDiscount("Student", isChild, isStudent);
return BigDecimal.valueOf(Math.min(childDiscount, studentDiscount))
.setScale(2, BigDecimal.ROUND_HALF_UP)
.doubleValue();
}
private double calculateDiscount(String discountType, boolean isChild, boolean isStudent) {
if ("Child".equals(discountType) && isChild) {
return 0.5;
}
if ("Student".equals(discountType) && isStudent) {
return 0.9 * baseDiscount;
}
return baseDiscount;
}
private double getTicketPrice(double discount, double basicPrice) {
return BigDecimal.valueOf(discount * basicPrice).setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();
}
private String getConsumerInfo(String name, int age, boolean isStudent, boolean isChild) {
return "consumerInfo" + Constant.LINE_SEPARATOR
+ "\tname: " + name + Constant.LINE_SEPARATOR
+ "\tage: " + age + Constant.LINE_SEPARATOR
+ "\tisStudent: " + isStudent + Constant.LINE_SEPARATOR
+ "\tisChild: " + isChild + Constant.LINE_SEPARATOR;
}
private String getPerformanceInfo(Performance performance) {
return "playInfo" + Constant.LINE_SEPARATOR
+ "\tplayName: " + performance.getPlayName() + Constant.LINE_SEPARATOR
+ "\tplayType: " + performance.getPlayType() + Constant.LINE_SEPARATOR
+ "\tdate: " + performance.getPlayDate() + Constant.LINE_SEPARATOR;
}
}
改进手法：移动函数至适合的类、移除标记参数
public class TicketInfo {
private final double baseDiscount;
public TicketInfo(double baseDiscount) {
this.baseDiscount = baseDiscount;
}
/**
* 获取票据信息
*
* @param consumer 客户信息
* @param performance 演出信息
* @param ageLimit 年龄限制
* @return 票据信息
*/
public String getTicketInfo(Consumer consumer, Performance performance, AgeLimit ageLimit) {
ageLimit.checkAge(consumer.getAge());
return performance.getPerformanceInfo()
+ consumer.getConsumerInfo()
+ getPriceInfo(consumer, performance);
}
private String getPriceInfo(Consumer consumer, Performance performance) {
final double discount = getDiscount(consumer);
final double ticketPrice = getTicketPrice(discount, performance.getBasicPrice());
return "priceInfo" + Constant.LINE_SEPARATOR
+ "\tprice: " + ticketPrice + Constant.LINE_SEPARATOR
+ "\tdiscount: " + discount + Constant.LINE_SEPARATOR;
}
private double getDiscount(Consumer consumer) {
double childDiscount = calculateChildDiscount(consumer);
double studentDiscount = calculateStudentDiscount(consumer);
return BigDecimal.valueOf(Math.min(childDiscount, studentDiscount))
.setScale(2, BigDecimal.ROUND_HALF_UP)
.doubleValue();
}
private double calculateChildDiscount(Consumer consumer) {
return consumer.isChild() ? 0.5 : baseDiscount;
}
private double calculateStudentDiscount(Consumer consumer) {
return consumer.isStudent() ? 0.9 * baseDiscount : baseDiscount;
}
private double getTicketPrice(double discount, double basicPrice) {
return BigDecimal.valueOf(discount * basicPrice).setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();
}
}
操作手法
| 操作 | 快捷键（推荐） | Ctrl+Alt+Shift+T（或：鼠标右键“Refactor”） | 注意 |
|---|---|---|---|
| 提炼函数 | Ctrl+Alt+M | Extract Method | |
| 搬移函数 | F6 | Move Instance Method | 需要先将方法变为静态方法 |
| 内联方法 | Ctrl+Atl+N | Inline Method | |
| 提取参数对象 | Ctrl+Alt+P | Parameter Object | |
| 添加入参 | Ctrl+F6/ Alt+Enter | Change Signature | |
| 删除无用入参 | Alt+Del / Alt+Enter |