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 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 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 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 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 getChildDeptList() {
return childDeptList;
}
public void setChildDeptList(List 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;
}
@NotNull
public 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;
}
@Override
public 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 getChildDeptList() {
return childDeptList;
}
public void setChildDeptList(List 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;
}
@NotNull
public 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;
}
@Override
public 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》