How to set a value of a variable of an object in an ArrayList

Question

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());
        }
    });
    }
}   

Answer 1

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