大家好，我是烤鴨：

? ? 今天說一下初始化對象的幾種方式：

? ????? 1.? ? 多參數構造器

? ? ????2.? ? 構建器

? ? ????3.? ? 構造器后 + get/set方法

舉個例子:

????這里有個機構entity，提供一個默認構造器

package com.xxx.xxx.modules.sys.entity;/*** 機構Entity* @version 2013-05-15*/ public class Office {private static final long serialVersionUID = 1L;private Area area; // 歸屬區域private String code; // 機構編碼private String type; // 機構類型（1：公司；2：部門；3：小組）private String grade; // 機構等級（1：一級；2：二級；3：三級；4：四級）private String address; // 聯系地址private String zipCode; // 郵政編碼private String master; // 負責人private String phone; // 電話private String fax; // 傳真private String email; // 郵箱private String useable;//是否可用private User primaryPerson;//主負責人private User deputyPerson;//副負責人private List<String> childDeptList;//快速添加子部門private String officeCode; //新增字段,門店id,和code值一樣private String businessArea; //2.0新增字段,營業面積private String businessHours; //2.0新增字段,營業時間public Office(){super();} }

如果想創建一個這樣的對象進行參數傳遞或者進行其他操作（數據庫等等）。

1.? ?多參數構造器

? ?? ??這是全參構造器:

public Office(Area area, String code, String type, String grade, String address, String zipCode, String master, String phone, String fax, String email, String useable, User primaryPerson, User deputyPerson, List<String> childDeptList, String officeCode, String businessArea, String businessHours, String jxName) {this.area = area;this.code = code;this.type = type;this.grade = grade;this.address = address;this.zipCode = zipCode;this.master = master;this.phone = phone;this.fax = fax;this.email = email;this.useable = useable;this.primaryPerson = primaryPerson;this.deputyPerson = deputyPerson;this.childDeptList = childDeptList;this.officeCode = officeCode;this.businessArea = businessArea;this.businessHours = businessHours;this.jxName = jxName;}

2.? ?構建器

?????這是全參構建器:

private Office(Office.Builder builder){this.id = builder.id;this.area = builder.area;this.code = builder.code;this.type = builder.type;this.grade = builder.grade;this.address = builder.address;this.name = builder.name;this.email = builder.email;this.phone = builder.phone;this.zipCode = builder.zipCode;this.master = builder.master;this.parent = builder.parent;this.parentIds = builder.parentIds;this.fax = builder.fax;this.sort = builder.sort;this.primaryPerson = builder.primaryPerson;this.deputyPerson = builder.deputyPerson;this.childDeptList = builder.childDeptList;this.officeCode = builder.officeCode;this.businessArea = builder.businessArea;this.useable = builder.useable;this.businessHours = builder.businessHours;this.delFlag = builder.delFlag;this.createBy = builder.createBy;this.updateBy = builder.updateBy;this.updateDate = builder.updateDate;this.createDate = builder.createDate;}//利用構建器創建對象public static class Builder extends Office{private static final long serialVersionUID = 1L;private Area area; // 歸屬區域private String code; // 機構編碼private String type; // 機構類型（1：公司；2：部門；3：小組）private String grade; // 機構等級（1：一級；2：二級；3：三級；4：四級）private String address; // 聯系地址private String zipCode; // 郵政編碼private String master; // 負責人private String phone; // 電話private String fax; // 傳真private String email; // 郵箱private String useable;//是否可用private User primaryPerson;//主負責人private User deputyPerson;//副負責人private List<String> childDeptList;//快速添加子部門private String officeCode; //新增字段,門店id,和code值一樣private String businessArea; //2.0新增字段,營業面積private String businessHours; //2.0新增字段,營業時間public Builder() {super();}public Builder id(String id){this.id = id;return this;}public Office build(){return new Office(this);}public Builder area(Area area){this.area = area;return this;}public Builder name(String name) {this.name = name;return this;}public Builder master(String master) {this.master = master;return this;}public Builder code(String code) {this.code = code;return this;}public Builder type(String type){this.type = type;return this;}public Builder grade(String grade) {this.grade = grade;return this;}public Builder address(String address) {this.address = address;return this;}public Builder zipCode(String zipCode) {this.zipCode = zipCode;return this;}public Builder password(String master) {this.master = master;return this;}public Builder parent(Office parent) {this.parent = parent;return this;}public Builder parentIds(String parentIds) {this.parentIds = parentIds;return this;}public Builder phone(String phone) {this.phone = phone;return this;}public Builder fax(String fax) {this.fax = fax;return this;}public Builder email(String email) {this.email = email;return this;}public Builder useable(String useable) {this.useable = useable;return this;}public Builder sort(Integer sort) {this.sort = sort;return this;}public Builder primaryPerson(User primaryPerson) {this.primaryPerson = primaryPerson;return this;}public Builder deputyPerson(User deputyPerson) {this.deputyPerson = deputyPerson;return this;}public Builder childDeptList(List<String> childDeptList) {this.childDeptList = childDeptList;return this;}public Builder officeCode(String officeCode) {this.officeCode = officeCode;return this;}public Builder businessArea(String businessArea) {this.businessArea = businessArea;return this;}public Builder businessHours(String businessHours) {this.businessHours = businessHours;return this;}public Builder delFlag(String delFlag) {this.delFlag = delFlag;if(StringUtils.isBlank(delFlag)){this.delFlag = IDBConstant.APPLICATION_DELETE_FLAG_VALID + "";}return this;}public Builder createBy(User createBy) {this.createBy = createBy;return this;}public Builder updateBy(User updateBy) {this.updateBy = updateBy;return this;}public Builder createDate(Date createDate) {this.createDate = createDate;return this;}public Builder updateDate(Date updateDate) {this.updateDate = updateDate;return this;}}

3.? ?get/set方法

???? 自動生成就行 ????????public List<String> getChildDeptList() {return childDeptList;}public void setChildDeptList(List<String> childDeptList) {this.childDeptList = childDeptList;}public String getUseable() {return useable;}public void setUseable(String useable) {this.useable = useable;}public User getPrimaryPerson() {return primaryPerson;}public void setPrimaryPerson(User primaryPerson) {this.primaryPerson = primaryPerson;}public User getDeputyPerson() {return deputyPerson;}public void setDeputyPerson(User deputyPerson) {this.deputyPerson = deputyPerson;}public Office getParent() {return parent;}public void setParent(Office parent) {this.parent = parent;}@NotNullpublic Area getArea() {return area;}public void setArea(Area area) {this.area = area;}@Length(min=1, max=1)public String getType() {return type;}public void setType(String type) {this.type = type;}@Length(min=1, max=1)public String getGrade() {return grade;}public void setGrade(String grade) {this.grade = grade;}@Length(min=0, max=255)public String getAddress() {return address;}public void setAddress(String address) {this.address = address;}@Length(min=0, max=100)public String getZipCode() {return zipCode;}public void setZipCode(String zipCode) {this.zipCode = zipCode;}@Length(min=0, max=100)public String getMaster() {return master;}public void setMaster(String master) {this.master = master;}@Length(min=0, max=200)public String getPhone() {return phone;}public void setPhone(String phone) {this.phone = phone;}@Length(min=0, max=200)public String getFax() {return fax;}public void setFax(String fax) {this.fax = fax;}@Length(min=0, max=200)public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}@Length(min=0, max=100)public String getCode() {return code;}public void setCode(String code) {this.code = code;}@Overridepublic String toString() {return name;}public String getOfficeCode() {return officeCode;}public void setOfficeCode(String officeCode) {this.officeCode = officeCode;}public String getBusinessArea() {return businessArea;}public void setBusinessArea(String businessArea) {this.businessArea = businessArea;}public String getBusinessHours() {return businessHours;}public void setBusinessHours(String businessHours) {this.businessHours = businessHours;} }public List<String> getChildDeptList() {return childDeptList;}public void setChildDeptList(List<String> childDeptList) {this.childDeptList = childDeptList;}public String getUseable() {return useable;}public void setUseable(String useable) {this.useable = useable;}public User getPrimaryPerson() {return primaryPerson;}public void setPrimaryPerson(User primaryPerson) {this.primaryPerson = primaryPerson;}public User getDeputyPerson() {return deputyPerson;}public void setDeputyPerson(User deputyPerson) {this.deputyPerson = deputyPerson;}public Office getParent() {return parent;}public void setParent(Office parent) {this.parent = parent;}@NotNullpublic Area getArea() {return area;}public void setArea(Area area) {this.area = area;}@Length(min=1, max=1)public String getType() {return type;}public void setType(String type) {this.type = type;}@Length(min=1, max=1)public String getGrade() {return grade;}public void setGrade(String grade) {this.grade = grade;}@Length(min=0, max=255)public String getAddress() {return address;}public void setAddress(String address) {this.address = address;}@Length(min=0, max=100)public String getZipCode() {return zipCode;}public void setZipCode(String zipCode) {this.zipCode = zipCode;}@Length(min=0, max=100)public String getMaster() {return master;}public void setMaster(String master) {this.master = master;}@Length(min=0, max=200)public String getPhone() {return phone;}public void setPhone(String phone) {this.phone = phone;}@Length(min=0, max=200)public String getFax() {return fax;}public void setFax(String fax) {this.fax = fax;}@Length(min=0, max=200)public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}@Length(min=0, max=100)public String getCode() {return code;}public void setCode(String code) {this.code = code;}@Overridepublic String toString() {return name;}public String getOfficeCode() {return officeCode;}public void setOfficeCode(String officeCode) {this.officeCode = officeCode;}public String getBusinessArea() {return businessArea;}public void setBusinessArea(String businessArea) {this.businessArea = businessArea;}public String getBusinessHours() {return businessHours;}public void setBusinessHours(String businessHours) {this.businessHours = businessHours;}

4.? ? 用法

????????如果我想構造一個對象

? ? 4.1? ? 構造器

????????直接上圖吧：

? ??

????當我new Office()的時候，我不知道需要傳入什么類型的參數，也不知道每個參數代表哪個字段。

多個字段的時候，不推薦這種方式。幾個字段算多？我覺得5+吧。

? ? 4.2??? 構建器

????

????? ? 上圖的字段比例子中的多了幾個，?構建器構造的對象很清晰，而且相對利于維護，構造器的話，需要修改構造方法，構建器在builder對象中加屬性就好了。為什么說構建器更安全，因為一個對象在可能有多個構造器，通過構造器來創建，沒法保證一致性。比如：new Office(id)和new Office(name)，這兩個對象怎么保證一致呢。

? ? 4.3? ? get/set方法

????? ? 不演示了，就拿上圖來說，set屬性需要多少行代碼？起碼多兩倍不止。

5.? ??關于構建器和構造器

????JavaBean模式自身有嚴重的缺點，因為構造過程被分到幾個調用中，在構造過程中Javabean可能處于不一致的狀態，類無法僅僅通過檢驗構造器參數的有效性來保證一致性。JavaBean模式阻止了把類做成不可變的可能，這就需要程序員付出額外的努力確保線程安全 。

Java中傳統的抽象工廠實現是Class對象，newInstance方法總是企圖調用類的無參構造器，這個構造器甚至可能根本不存在。Class.newInstance破壞了編譯時的異常檢查。Builder模式也存在不足。為了創建對象，必須先創建它的構建器。在十分注重性能的情況下，可能就成問題了。Builder模式還比重疊構造器模式更加冗長，因此它只在有很多參數的時候才使用，比如4個或者更多個參數。通常最好一開始就使用構建器。

　　如果類的構造器或者靜態工廠中具有多個參數，設計這種類時，Builder模式就是種不錯的選擇，特別是當大多數參數都是可選的時候。與使用傳統的重疊構造器模式相比，使用Builder模式的客戶端代碼將更易于閱讀和編寫，構建器也比JavaBeans更加安全。

　參考資料

《Effective Java 中文版 第2版》?

????????

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