如何设置一个对象的变量的值在一个ArrayList [英] How to set a value of a variable of an object in an ArrayList

问题描述

我的工作分配中，我有：

1. 创建具有以下属性/变量的Employee类：
   名称
   年龄
   部门




2. 创建一个名为Department类其中将包含员工的列表。

   一个。 Department类将有将返回其员工按年龄排序的方法。

   乙。系数值只能是下列之一：

   
   
   • 会计学
   
   
   • 市场营销
   
   
   • 人力资源
   
   
   • 信息系统
   
   

我有困难的时候试图找出如何完成2B。
以下是我迄今为止：

 进口的java.util。*;公共类Employee {
字符串名称;
INT年龄;
串部门;员工（字符串名称，诠释年龄，弦乐部）{
    this.name =名称;
    this.age =年龄;
    this.department =部;}
INT getAge（）{
    返回年龄;
}
}类系{
公共静态无效的主要（字串[] args）{
    清单＆LT;员工＆GT; empList =新的ArrayList＆LT;员工＆GT;（）;    Collections.sort（empList，新的比较＆LT;员工＆GT;（）{
        公众诠释比较（员工E1，E2员工）{
            返回新的整数（e1.getAge（））的compareTo（e2.getAge（））;
        }
    }）;
    }
}
 

解决方案

您可以使用，这将限制你只能使用指定的值相同的目的枚举。
声明你的处枚举如下：

 公共枚举系{    会计，Marketting，Human_Resources，Information_Systems}
 

现在

您员工类可以是

 公共类Employee {
    字符串名称;
    INT年龄;
    系部;    员工（字符串名称，诠释年龄，系部）{
        this.name =名称;
        this.age =年龄;
        this.department =部;    }    INT getAge（）{
        返回年龄;
    }
}
 

和同时创造员工，你可以使用

 员工员工=新员工（普拉萨德，47，Department.Information_Systems）;
 

修改按阿德里安深当然，因为它是一个伟大的建议的建议。

• 的枚举是这就是为什么其良好的大写字母根据Java约定声明常量。


• 但是，我们不希望枚举的资本重新presentation待观察，所以我们可以创建枚举构造，并通过读取信息给它。



• 我们西港岛线修改枚举包括的toString（）方法和构造，它接受一个字符串参数。

   公共枚举系{   会计（会计），MARKETTING（Marketting），HUMAN_RESOURCES（
          人力资源），INFORMATION_SYSTEMS（信息系统）;   私人字符串DEPTNAME;    部（字符串DEPTNAME）{
         this.deptName = DEPTNAME;
      }   @覆盖
     公共字符串的toString（）{
      返回this.deptName;
     }}
   

所以，当我们正在创建一个员工对象，如下所示，使用它

 员工员工=新员工（普拉萨德Kharkar，47，Department.INFORMATION_SYSTEMS）;
的System.out.println（employee.getDepartment（））;
 

我们会得到一个可读的字符串重新presentation为信息系统因为它是由返回的toString（）方法，它是通过的System.out.println（）语句。
阅读关于枚举

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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