JAVA构造对象的几种方式（构建器、构造器）

大家好，我是烤鸭：

    今天说一下初始化对象的几种方式：

        1.    多参数构造器

        2.    构建器

        3.    构造器后 + get/set方法


举个例子:

    这里有个机构entity，提供一个默认构造器

package com.xxx.xxx.modules.sys.entity;/*** 机构Entity* @version 2013-05-15*/
public class Office {private static final long serialVersionUID = 1L;private Area area;		// 归属区域private String code; 	// 机构编码private String type; 	// 机构类型（1：公司；2：部门；3：小组）private String grade; 	// 机构等级（1：一级；2：二级；3：三级；4：四级）private String address; // 联系地址private String zipCode; // 邮政编码private String master; 	// 负责人private String phone; 	// 电话private String fax; 	// 传真private String email; 	// 邮箱private String useable;//是否可用private User primaryPerson;//主负责人private User deputyPerson;//副负责人private List<String> childDeptList;//快速添加子部门private String officeCode; //新增字段,门店id,和code值一样private String businessArea; //2.0新增字段,营业面积private String businessHours; //2.0新增字段,营业时间public Office(){super();}
}

如果想创建一个这样的对象进行参数传递或者进行其他操作（数据库等等）。


1.   多参数构造器

       这是全参构造器:

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.   构建器

     这是全参构建器:

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;}//利用构建器创建对象public static class Builder extends Office{private static final long serialVersionUID = 1L;private Area area;		// 归属区域private String code; 	// 机构编码private String type; 	// 机构类型（1：公司；2：部门；3：小组）private String grade; 	// 机构等级（1：一级；2：二级；3：三级；4：四级）private String address; // 联系地址private String zipCode; // 邮政编码private String master; 	// 负责人private String phone; 	// 电话private String fax; 	// 传真private String email; 	// 邮箱private String useable;//是否可用private User primaryPerson;//主负责人private User deputyPerson;//副负责人private List<String> childDeptList;//快速添加子部门private String officeCode; //新增字段,门店id,和code值一样private String businessArea; //2.0新增字段,营业面积private String businessHours; //2.0新增字段,营业时间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

     自动生成就行 
        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

        如果我想构造一个对象

    4.1    构造器

        直接上图吧：

    

    当我new Office()的时候，我不知道需要传入什么类型的参数，也不知道每个参数代表哪个字段。

多个字段的时候，不推荐这种方式。几个字段算多？我觉得5+吧。

    4.2    构建器

    

        上图的字段比例子中的多了几个， 构建器构造的对象很清晰，而且相对利于维护，构造器的话，需要修改构造方法，构建器在builder对象中加属性就好了。为什么说构建器更安全，因为一个对象在可能有多个构造器，通过构造器来创建，没法保证一致性。比如：new Office(id)和new Office(name)，这两个对象怎么保证一致呢。

    4.3    get/set方法

        不演示了，就拿上图来说，set属性需要多少行代码？起码多两倍不止。


5.    关于构建器和构造器

    JavaBean模式自身有严重的缺点，因为构造过程被分到几个调用中，在构造过程中Javabean可能处于不一致的状态，类无法仅仅通过检验构造器参数的有效性来保证一致性。JavaBean模式阻止了把类做成不可变的可能，这就需要程序员付出额外的努力确保线程安全 。

Java中传统的抽象工厂实现是Class对象，newInstance方法总是企图调用类的无参构造器，这个构造器甚至可能根本不存在。Class.newInstance破坏了编译时的异常检查。Builder模式也存在不足。为了创建对象，必须先创建它的构建器。在十分注重性能的情况下，可能就成问题了。Builder模式还比重叠构造器模式更加冗长，因此它只在有很多参数的时候才使用，比如4个或者更多个参数。通常最好一开始就使用构建器。

　　如果类的构造器或者静态工厂中具有多个参数，设计这种类时，Builder模式就是种不错的选择，特别是当大多数参数都是可选的时候。与使用传统的重叠构造器模式相比，使用Builder模式的客户端代码将更易于阅读和编写，构建器也比JavaBeans更加安全。


　参考资料

《Effective Java 中文版 第2版》 


        

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