如何在ArrayList中设置对象的变量值 [英] How to set a value of a variable of an object in an ArrayList

问题描述

我正在完成一项任务，我必须:

1. 创建一个具有以下属性/变量的 Employee 类:姓名年龄部门

2. 创建一个名为 Department 的类，其中将包含员工列表.

   一个.Department 类将有一个方法可以返回按年龄排序的员工.

   B.Department 的值只能是以下之一:

   • 会计"
   • 营销"
   • 人力资源"
   • 信息系统"

我最难的是弄清楚如何完成 2b.这是我目前所拥有的:

import java.util.*;公共类员工{字符串名称；年龄；弦部；员工(字符串名称，整数年龄，字符串部门){this.name = 名称；this.age = 年龄；this.department = 部门；}int getAge() {回归年龄；}}课部{公共静态无效主(字符串 [] args){ListempList = new ArrayList();Collections.sort (empList, new Comparator() {公共 int 比较(员工 e1，员工 e2){返回新整数 (e1.getAge()).compareTo(e2.getAge());}});}}

解决方案

您可以将枚举用于相同的目的，这将限制您只能使用指定的值.声明你的 Department 枚举如下

公共枚举部门{会计、市场营销、人力资源、信息系统}

你的Employee类现在可以

公共类员工{字符串名称；年龄；部门部门；员工(字符串名称，整数年龄，部门部门){this.name = 名称；this.age = 年龄；this.department = 部门；}int getAge() {回归年龄；}}

在创建员工时，您可以使用

Employee employee = new Employee("Prasad", 47, Department.Information_Systems);

EDIT 按照 Adrian Shum 的建议，当然因为这是一个很好的建议.

• 枚举是常量，这就是为什么根据java约定用大写字母声明是好的.
• 但是我们不希望看到枚举的大写表示，因此我们可以创建枚举构造函数并将可读信息传递给它.

• 我们将修改枚举以包含 toString() 方法和采用字符串参数的 constructor.

   公共枚举部门{会计(会计")，营销(营销")，HUMAN_RESOURCES("人力资源"), INFORMATION_SYSTEMS("信息系统");私人字符串部门名称；部门(字符串部门名称){this.deptName = 部门名称；}@覆盖公共字符串 toString() {返回 this.deptName;}}

所以当我们创建一个 Employee 对象并使用它时，

Employee employee = new Employee("Prasad Kharkar", 47, Department.INFORMATION_SYSTEMS);System.out.println(employee.getDepartment());

我们将得到一个可读的字符串表示，如 Information Systems，因为它由 toString() 方法返回，该方法被 System.out.println() 语句.阅读关于枚举的优秀教程>

I am working on an assignment in which I have to:

1. Create an Employee class with the following attributes/variables: name age department

2. Create a class called Department which will contain a list of employees.

   a. Department class will have a method which will return its employees ordered by age.

   b. Value of Department can be only one of the following:

   • "Accounting"
   • "Marketing"
   • "Human Resources"
   • "Information Systems"

I am having the hardest time trying to figure out how to complete 2b. Here is what I have so far:

import java.util.*;

public class Employee {
String name; 
int age;
String department;

Employee (String name, int age, String department) {
    this.name = name;
    this.age = age;
    this.department = department;

}
int getAge() {
    return age;
}
}

class Department {
public static void main(String[] args) {
    List<Employee>empList = new ArrayList<Employee>();

    Collections.sort (empList, new Comparator<Employee>() {
        public int compare (Employee e1, Employee e2) {
            return new Integer (e1.getAge()).compareTo(e2.getAge());
        }
    });
    }
}   

解决方案

You can use enumerations for the same purpose which will restrict you to use only specified values. Declare your Department enum as follows

public enum Department {

    Accounting, Marketting, Human_Resources, Information_Systems

}

You Employee class can now be

public class Employee {
    String name;
    int age;
    Department department;

    Employee(String name, int age, Department department) {
        this.name = name;
        this.age = age;
        this.department = department;

    }

    int getAge() {
        return age;
    }
}

and while creating employee, you can use

Employee employee = new Employee("Prasad", 47, Department.Information_Systems);

EDIT as suggested by Adrian Shum and of course because it is a great suggestion.

• The enums are constants thats why its good to be declared in capital letters according to java conventions.
• But we don't want the capital representation of the enums to be seen so we can create enum constructors and pass readable info to it.

• We wil modify enum to include toString() method and constructor which takes a string argument.

   public enum Department {
  
     ACCOUNTING("Accounting"), MARKETTING("Marketting"), HUMAN_RESOURCES(
          "Human Resources"), INFORMATION_SYSTEMS("Information Systems");
  
     private String deptName;
  
      Department(String deptName) {
         this.deptName = deptName;
      }
  
     @Override
     public String toString() {
      return this.deptName;
     }
  
  }
  

So when we are creating an Employee object as follows and using it,

Employee employee = new Employee("Prasad Kharkar", 47, Department.INFORMATION_SYSTEMS);
System.out.println(employee.getDepartment()); 

We will get a readable string representation as Information Systems as it is returned by toString() method which is called implicitly by System.out.println() statement. Read the good tutorial about Enumerations

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