从本身是目标对象的变量的对象访问Java对象的变量？答案

【问题标题】：Access a Java object's variables from an object which is itself a variable of the target object?从本身是目标对象的变量的对象访问Java对象的变量？
【发布时间】：2021-09-25 23:38:39
【问题描述】：

我写了三个 Java 类：

Company
Department
Employee

每个Company 对象都包含一个Department 对象数组，而这些对象又包含Employee 对象数组。

我想在Employee 类setQid() 中编写一个方法，该方法将为该员工设置一个唯一ID，格式如下：

compName_deptName_deptNumber_empFirstName_empSurname

例子：

“Microsoft_Accounting_3_John_Smith”

我的问题是：如何从 Employee 类的上下文中访问以下变量？

String name 在Company
String name 在Department
int number 在Department

请看我下面的代码：

public class Company {

    private String name;
    private Department[] departments;

    public Company(String name, Department[] departments) {

        this.name = name;
        this.departments = departments;
    }
}


public class Department {

    private String name;
    private int number;
    private Employee[] members;

    public Department(String name, int number, Employee[] members) {

        this.name = name;
        this.number = number;
        this.members = members;
    }
}


public class Employee {

    private String firstname;
    private String surname;
    private String qid; //A unique employee ID

    public Employee(String firstname, String surname) {

        this.firstname = firstname;
        this.surname = surname;
        setQid();
    }

    public void setQid() {

        // How can I access the Company name, Department name, and Department number from here?
    }
}

【问题讨论】：

你不能。在您当前的设置中，Employee 没有Company，您可以凭空创建一个新的Employee，而无需在任何地方定义任何Company。
@luk2302 但是Company 有一个Department 有一个Employee 对吗？没有办法访问这个方向的数据？
如果您只是参考Employee，则不会。
我想我将不得不重新考虑我的班级结构。谢谢你们。

标签： java class object oop

【解决方案1】：

您需要在您的 Employee 类中有一个 Department 的引用，并在您的 Department 中有一个 Company 的引用，只有这样您的实体之间的关系才会完整。

public class Company {

    private String name;
    private Department[] departments;

    public Company(String name, Department[] departments) {

        this.name = name;
        this.departments = departments;
    }
    //add getters and setters
}

public class Department {

    private String name;
    private int number;
    private Employee[] members;
    private Company company;

    public Department(String name, int number, Employee[] members) {

        this.name = name;
        this.number = number;
        this.members = members;
    }


    //add getters and setters
}

public class Employee {

    private String firstname;
    private String surname;
    private String qid; //A unique employee ID
    private Department department;

    public Employee(String firstname, String surname) {

        this.firstname = firstname;
        this.surname = surname;
        setQid();
    }

    public void setQid() {
     
      qid = department.getCompany().getName + "_" + department.getName() ....

    }

    //add getters and setters
}

【讨论】：