Question

Basically, I have a Container class called “Employees” which has in it an ArrayList. This ArrayList contains “Employee” objects, which in turn contain “EmployeeData” objects which in turn contain String objects such as “first” or “last” (which are employee names).

Here’s a diagram of the ArrayList structure:

ArrayList[Employee] emps ==> 1:Many ==> Employee emp
Employee emp ==> 1:1 ==> EmployeeData data
EmployeeData data ==> 1:2 ==> String last // A string that contains employee's last name.

How in the world would I perform a quicksort on the ArrayList so that the “Employee” objects in it are in alphabetical order based on the String object “last”? It seems kinda complicated!

---

Here’s a basic design of my classes:

class Employees{
    //data:
        private ArrayList<Employee> emps = new ArrayList<Employee>();

    //Some constructors go here

    //Methods to add, remove, toString, etc, go here

    public /*output a sorted ArrayList?*/ sort(){
        // Some kind of "quicksort" in here to modify or create a new ArrayList sorted by employee's las name...
    }
}

class Employee{
    //data:
    EmployeeData data;
    // Some methods to construct and modify EmployeeData data.
}

class EmployeeData{
    //data:
        String first, last; // I wish to sort with "last". How do you do it?
        double payrate, hours;
    //...methods...
}

As you can see, those are the classes. I have no idea how to implement “sort” in the “Employees” class so that it sorts the ArrayList by the “last” variable of the “EmployeeData” class.

Answer 1

The best practice is to encapsulate the sorting logic in the class stored in the ArrayList, Employee in this case. Implement Comparable by creating a compareTo(Employee) method.

import java.util.*;

public class Employee  implements Comparable<Employee> {
    public EmployeeData Data;

    public Employee(String first, String last)
    {
        Data = new EmployeeData(first, last);
    }

    public int compareTo(Employee other)
    {
        return Data.Last.compareTo(other.Data.Last);
    }

    public String toString() {
        return Data.First + " " + Data.Last;
    }

    public static void main(String[] args) throws java.io.IOException {
        ArrayList list = new ArrayList();
        list.add(new Employee("Andy", "Smith"));
        list.add(new Employee("John", "Williams"));
        list.add(new Employee("Bob", "Jones"));
        list.add(new Employee("Abraham", "Abrams"));
        Collections.sort(list);
        for (int i = 0; i < list.size(); i++)
        {
            System.out.println(list.get(i));
        }
        System.in.read();
    }
}

public class EmployeeData {
    public String First;
    public String Last;
    public EmployeeData(String first, String last)
    {
        First = first;
        Last = last;
    }
}

Output:

Abraham Abrams
Bob Jones
Andy Smith
John Williams