How to sort object arrays by parameter using Comparable Interface in Java?

Question

I am currently working on an assignment and I am almost done except for one part.

I need to sort some of the objects in the array based on whether they are in Accounting or Information Systems. I setup the compareTo method but I do not believe I did it right or else I just don't know how to call on it as I did and it is not doing what I thought it would do.

This is driving me nuts as it is the last thing I have to do and I can't figure it out, any help would be great.

Here is the Comparable Inteface

public interface Comparable {


public abstract int compareTo(Employee c);


}//end comparable

Here is my code in the Department class:

public class Department implements Comparable  {

public int compareTo(Employee e){
    int compareAge = ((Employee) e).getAge();

    return e.getAge() - compareAge;
}//end


}//end department

Here is my code for the main method:

public class Company {


public static void main(String [] args){

    Employee[] e = new Employee[13];
    PrimeAgeChecker p = new PrimeAgeChecker();
    Department d = new Department();

    e[0] = new Employee("Counting Guru",55,"Accounting");
    e[1] = new Employee("Counting Pro",45,"Accounting");
    e[2] = new Employee("Counting Savvy",40,"Accounting");
    e[3] = new Employee("Counting Novice",25,"Accounting");
    e[4] = new Employee("Sales Guru",50,"Marketing");
    e[5] = new Employee("Sales Pro",48,"Marketing");
    e[6] = new Employee("Sales Savvy",38,"Marketing");
    e[7] = new Employee("Hiring Guru",58,"Human Resrouces");
    e[8] = new Employee("Hiring Pro",47,"Human Resrouces");
    e[9] = new Employee("Hacking Pro",47,"Information Systems");
    e[10] = new Employee("Hacking Guru",51,"Information Systems");
    e[11] = new Employee("Hacking Savvy",38,"Information Systems");
    e[12] = new Employee("Hacking Novice",23,"Information Systems");


    for(int i = 0;i<e.length;i++){
        if(e[i].getDept().equals("Accounting") || e[i].getDept().equals("Information Systems")){
            d.compareTo(e[i]);
            System.out.println(e[i]);
        }//end if
        else{
        System.out.println(e[i] + " " + p.isPrime(e[i]));
        }

    }//end 





}//end main
}//end company

P.S. Sorting the ages of Employees code HAS to go into the Department Class as per the assignment instructions

Note: in an interface, the modifiers public and abstract are implied, no need to specify them — fge
– fge, Commented Mar 17, 2014 at 22:47
I get this error warning when I do that. "The type Comparable is not generic; it cannot be parameterized with arguments <Employee>" — MrTimotheos
– MrTimotheos, Commented Mar 17, 2014 at 22:49
Comparable is an interface from the java.lang package. Defining your own Comparable class is a very bad idea - it will only lead to confusion for anyone (including you) reading your code. Name it something else, or use the java.lang.Comparable interface instead. — Bohemian
– Bohemian ♦, Commented Mar 17, 2014 at 22:56
Seems to be a remarkably precise duplicate of stackoverflow.com/a/21659849 — Marco13
– Marco13, Commented Mar 17, 2014 at 23:14

libik · Accepted Answer · 2014-03-17 22:48:37Z

1

There it is wrong :

int compareAge = ((Employee) e).getAge();
return e.getAge() - compareAge;

If you look closely, this always returns 0, because this ((Employee) e).getAge(); is same as e.getAge()

answered Mar 17, 2014 at 22:48

libik

23.1k10 gold badges52 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

MrTimotheos Over a year ago

Ah yeah I see that now. I'm not sure what to change that to though.

fge Over a year ago

Uh, just `Integer.compare(age, e.age) is enough; no need to cast, no need to use setters

libik Over a year ago

@MrTimotheos - probably think it through. Why you compare employee age in department instance? It does not make sense :)

MrTimotheos Over a year ago

The only problem is that here is not an age variable in the Department class yet the assignment wants me to write a method that sorts the ages in Department class

MrTimotheos Over a year ago

@libik I understand but that's what the assignment wants me to do and It's making my head swirl. I have no idea how to approach this problem.

|

La-comadreja · Accepted Answer · 2014-03-17 22:49:22Z

1

Firstly, you should implement compareTo() in class Employee, not in Department.

In class Employee, here is how the method should read:

if (this.getDept().compareTo(other.getDept()) != 0) 
    return this.getDept().compareTo(other.getDept());
return this.getAge() - e.getAge();

answered Mar 17, 2014 at 22:49

La-comadreja

5,74512 gold badges38 silver badges64 bronze badges

5 Comments

libik Over a year ago

it would probably not work, because class Department does not have age (or at least it should not have one :D )

MrTimotheos Over a year ago

Yeah it won't. that's the tricky part. How do I compare two employee's ages and then sort them in ascending order? It's a puzzle, I tell ya.

La-comadreja Over a year ago

@libik fixed as per your comment.

MrTimotheos Over a year ago

@La-comadreja I appreciate that, as that would be the simple solution. However my assignment explicitly states to sort the Employees by their age in the Department class

La-comadreja Over a year ago

yes, so you should call the compareTo() method in class Employee from class Department. That's what I think they mean.

Collectives™ on Stack Overflow

How to sort object arrays by parameter using Comparable Interface in Java?

2 Answers 2

7 Comments

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related