场景和问题
在Java开发时，需要来回交换大量的数据，比如要为方法传入参数，也要获取方法的返回值，该如何能更好的进行数据的交互？

基本的编写步骤
◎第1步：写一个类，实现可序列化（如果以后数据是往数据库里存的，那么可以不序列化，节省资源）
◎第2步：私有化所有属性，保持一个默认构造方法(public无参)
◎第3步：为每个属性提供get()、set()方法（如果是boolean型变量，最好把get改成is）
◎第4步：推荐覆盖实现equals()、hashCode()和toString()方法

值对象的本质是“封装数据”
User 类：

package cn.hncu.pattern.factory.vo.v2.vo;

import java.io.Serializable;

public class User implements Serializable{
    //只能将支持 java.io.Serializable 接口的对象写入流中,必须实现这个接口
    private String userId;
    private String tel;
    private String address;
    private int age;
    private boolean isMale;
    public User() {
    }

    public User(String userId, String tel, String address, int age){
        this.userId = userId;
        this.tel = tel;
        this.address = address;
        this.age = age;
    }

    public String getTel() {
        return tel;
    }
    public void setTel(String tel) {
        this.tel = tel;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getUserId() {
        return userId;
    }
    public void setUserId(String userId) {
        this.userId = userId;
    }
    public boolean isMale() {
        return isMale;
    }
    public void setMale(boolean isMale) {
        this.isMale = isMale;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((userId == null) ? 0 : userId.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        User other = (User) obj;
        if (userId == null) {
            if (other.userId != null)
                return false;
        } else if (!userId.equals(other.userId))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "User [userId=" + userId + ", tel=" + tel + ", address="
                + address + ", age=" + age + "]";
    }


}

B类：

package cn.hncu.pattern.factory.vo.v2;

import cn.hncu.pattern.factory.vo.v2.vo.User;


public class B {
    String userId=null;
    User user = null;
    public boolean sendData(User user){ //Value Object ----Model
        System.out.println("数据已经接受到。。。");
        operate(user);
        return true;
    }
    private void operate(User user) {
        this.user = user;
        this.user.setUserId("CN_"+user.getUserId());
        System.out.println("处理数据...");
    }

    public User getData(){
        return user;
    }

    public String getUserId(){
        return userId;
    }

}

A类：

package cn.hncu.pattern.factory.vo.v2;

import cn.hncu.pattern.factory.vo.v2.vo.User;


public class A {
    public static void main(String[] args) {
        B obj = new B();
        User user = new User("A001", "13512345678", "hncu",20);

        obj.sendData(user);
        User data = obj.getData();

        System.out.println( data.getUserId() );
        System.out.println(data);
        User user2 = new User();
        user2.setAge(21);
        user2.setUserId("A002");
        System.out.println(user2);
        obj.sendData(user2);
        System.out.println(user2);
        //可以做得更好的： 
        // Id可以用唱票模型 2318,2319,......

    }

}

输出:

数据已经接受到。。。
处理数据...
CN_A001
User [userId=CN_A001, tel=13512345678, address=hncu, age=20]
User [userId=A002, tel=null, address=null, age=21]
数据已经接受到。。。
处理数据...
User [userId=CN_A002, tel=null, address=null, age=21]