重構--Java方法參數過多

• 示例方法

public void getNews(Context context,
                        Callback callback,
                        String uuid,
                        String uid,
                        String from,
                        String token,
                        String uid,
                        String .....){
                        //邏輯
}

• 示例構造函數

public class Person {
    public String lastName;
    public String firstName;
    public String middleName;
    public String salutation;
    public String suffix;
    public String streetAddress;
    public String city;
    public String state;
    public boolean isFemale;
    public boolean isEmployed;
    public boolean isHomeOwner;
    public Person(String lastName, String firstName, String middleName, String salutation,
                  String suffix, String streetAddress, String city, String state,
                  boolean isFemale, boolean isEmployed, boolean isHomeOwner) {
        this.lastName = lastName;
        this.firstName = firstName;
        this.middleName = middleName;
        this.salutation = salutation;
        this.suffix = suffix;
        this.streetAddress = streetAddress;
        this.city = city;
        this.state = state;
        this.isFemale = isFemale;
        this.isEmployed = isEmployed;
        this.isHomeOwner = isHomeOwner;
    }
}

• 問題：

  • 添加大量參數理解難度

  • 易參數位置不正確且運行正常

  • 不易維護

  • 那一個方法或者構造方法多少個參數才好了--沒有答案

    • Robert Martin在Clean Code寫到

    函數參數的理想個數是零，其次是一，緊隨其后的是二，應該盡可能避免三個參數的情況。參數如果多于三個則需要特殊的理由，而且無論如何都不應該再使用。
    

    • Steve McConnell在Code Complete中寫到：開發者應該限制參數在七個以內

解決方法

• 引入參數對象
  • 參數關系緊密合并到一個對象中
    • Person.class

public class Person {
    public FullName fullName;
    public Address address;
    public boolean isFemale;
    public boolean isEmployed;
    public boolean isHomeOwner;
    public Person(FullName fullName, Address address, boolean isFemale, boolean isEmployed, boolean isHomeOwner) {
        this.fullName = fullName;
        this.address = address;
        this.isFemale = isFemale;
        this.isEmployed = isEmployed;
        this.isHomeOwner = isHomeOwner;
    }
}

• FullName.class

public class FullName {
    public String lastName;
    public String firstName;
    public String middleName;
    public String salutation;
    public String suffix;
    public FullName(String lastName, String firstName, String middleName, String salutation, String suffix) {
        this.lastName = lastName;
        this.firstName = firstName;
        this.middleName = middleName;
        this.salutation = salutation;
        this.suffix = suffix;
    }
}

• Address.class

 public class Address {
    public String streetAddress;
    public String city;
    public String state;
    public Address(String streetAddress, String city, 
                              String state) {
        this.streetAddress = streetAddress;
        this.city = city;
        this.state = state;
    }
}

• 問題：參數對象可能被濫用。如果一個開發者純粹為了減少參數數量，把聯系不緊的幾個參數強捆在一個類中這肯定是行不通的，在可讀性上甚至適得其反。
• Builder模式：
  • 需求：當一個對象需要不同的參數構造方法？不能寫5*5滿足所有的需求吧
  • 適用范圍：構建對象時，如果碰到類有很多參數——其中很多參數類型相同而且很多參數可以為空時，使用Builder模式來完成。當參數數量不多、類型不同而且都是必須出現時，通過增加代碼實現Builder往往無法體現它的優勢。在這種情況下，理想的方法是調用傳統的構造函數。再者，如果不需要保持不變，那么就使用無參構造函數調用相應的set方法吧。
  • 代碼
  • Person.class

public class Person {
    public FullName fullName;
    public Address address;
    public boolean isFemale;
    public boolean isEmployed;
    public boolean isHomeOwner;
    public Person(FullName fullName, Address address, boolean isFemale, boolean isEmployed, boolean isHomeOwner) {
        this.fullName = fullName;
        this.address = address;
        this.isFemale = isFemale;
        this.isEmployed = isEmployed;
        this.isHomeOwner = isHomeOwner;
    }
      public static class Builder {
        private FullName fullName;
        private Address address;
        private boolean isFemale;
        private boolean isEmployed;
        private boolean isHomeOwner;
        /**
         * 如果有必填參數這里可以構造必填構造方法
         */
        public Builder() {
        }
        public Builder setFullName(FullName fullName) {
            this.fullName = fullName;
            return this;
        }
        public Builder setAddress(Address address) {
            this.address = address;
            return this;
        }
        public Builder setFemale(boolean female) {
            isFemale = female;
            return this;
        }
        public Builder setEmployed(boolean employed) {
            isEmployed = employed;
            return this;
        }
        public Builder setHomeOwner(boolean homeOwner) {
            isHomeOwner = homeOwner;
            return this;
        }
        public Person create() {
            return new Person(fullName, address, isFemale, isEmployed, isHomeOwner);
        }
    }
}

• FullName.class

public class FullName {
    public String lastName;
    public String firstName;
    public String middleName;
    public String salutation;
    public String suffix;
    public FullName(String lastName, String firstName, String middleName, String salutation, String suffix) {
        this.lastName = lastName;
        this.firstName = firstName;
        this.middleName = middleName;
        this.salutation = salutation;
        this.suffix = suffix;
    }
    public static class Builder {
        private String lastName;
        private String firstName;
        private String middleName;
        private String salutation;
        private String suffix;
        public Builder() {
        }
        public Builder setLastName(String lastName) {
            this.lastName = lastName;
            return this;
        }
        public Builder setFirstName(String firstName) {
            this.firstName = firstName;
            return this;
        }
        public Builder setMiddleName(String middleName) {
            this.middleName = middleName;
            return this;
        }
        public Builder setSalutation(String salutation) {
            this.salutation = salutation;
            return this;
        }
        public Builder setSuffix(String suffix) {
            this.suffix = suffix;
            return this;
        }
        public FullName create() {
            return new FullName(lastName, firstName, middleName, salutation, suffix);
        }
    }
}

• Address.class

public class Address {
    public String streetAddress;
    public String city;
    public String state;
    public Address(String streetAddress, String city, String state) {
        this.streetAddress = streetAddress;
        this.city = city;
        this.state = state;
    }
    public static class Builder {
        private String streetAddress;
        private String city;
        private String state;
        public Builder() {
        }
        public Builder setStreetAddress(String streetAddress) {
            this.streetAddress = streetAddress;
            return this;
        }
        public Builder setCity(String city) {
            this.city = city;
            return this;
        }
        public Builder setState(String state) {
            this.state = state;
            return this;
        }
        public Address create() {
            return new Address(streetAddress, city, state);
        }
    }
}

調用的地方

public static void main(String[] args) {
        FullName fullName = new FullName.Builder().setFirstName("yes")
                .setLastName("no").create();
        Address address = new Address.Builder().setCity("china").setState("12")
                .create();
        Person person = new Person.Builder().setAddress(address)
                .setFullName(fullName).create();
    }

• 優點：客戶端代碼的可用性和可讀性得到了大大提高，構造函數的參數數量明顯減少調用起來非常直觀。單個builder構建多個對象時Builder參數可在創建期間進行調整，還可以根據對象不同而進行改變，有效的避免重載構造函數。

• 缺點：增加代碼量，代碼變得更加冗長(相比較參數數量的增加，相同類型的參數混在一起，可選參數的增加而言，改善代碼可讀性更有價值)

• 重載

  • 適用范圍：方法中參數可選參數或者參數中指定參數相同
  • 代碼

  public String name(String name,int year) {
      return name+year;
  }
  /**
   * 重載
   * @param name
   * @return
   */
  public String name(String name) {
      return name+"null";
  }
  

  • 優點：遇到可選參數或者默認參數時，使用方法重載會十分有效。

• 參考資料

  • ImportNew