Sort an ArrayList by an object's attribute in java

Question

I wish to sort my objects in order of their Email address.

This is the method I've attempted but it does not work, but I'm not even sure it's the correct way to do what I want?

public static ArrayList<Billing> sortedListByEmail(ArrayList<Billing> Billing) {
    ArrayList<Billing> Sort = new ArrayList<Billing>();

    for (int i = 0; i < Sort.size(); i++) {
        Collections.sort(Sort, new Comparator<Billing>() {
            public int compare(Billing o1, Billing o2) {
                return o1.getEmail() > o2.getEmail() ? -1 : o1.getEmail().equals(o2.getEmail() ? 0 : 1);
            }
        });
    }

    return Sort;
}

Rest of the class:

import java.util.ArrayList;
import java.util.Collections;
import java.lang.Comparable;
import java.util.Comparator;

public class Billing extends User implements Comparable<User> {
    private Address billingAddress;
    private String email;

    public Billing(String id, String firstName, String lastName, String userName, String password, UserType userType, PermissionType permission, Boolean Status, Address billingAddress, String email) {
        super(id, firstName, lastName, userName, password, userType, permission, Status);

        this.billingAddress = billingAddress;
        this.email = email;
    }

    public Billing(String id, String firstName, String lastName, String userName, String password, UserType userType, PermissionType permission, Boolean Status, String email) {
        super(id, firstName, lastName, userName, password, userType, permission, Status);

    }

    public Billing(String id, String firstName, String lastName, String userName, String password, UserType userType, PermissionType permission, Boolean Status) {
        super(id, firstName, lastName, userName, password, userType, permission, Status);
    }

    public Address getBillingAddress() {
        return billingAddress;
    }

    public void setBillingAddress(Address billingAddress) {
        this.billingAddress = billingAddress;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

How would I accomplish sorting the objects in order of their email address? Thank you

You shouldn't be sorting the list in a loop. Also, since the email is a String, why not just use String.CASE_INSENSITIVE_ORDER as the comparator? — Balz Guenat, Sep 10 '19 at 12:32
Btw. why are you calling `.sort()` on an empty list and inside of a loop? — Amongalen, Sep 10 '19 at 12:32
@Amongalen im really just mucking around the code to see what works so alot of what ive posted probably doesnt make sense but i just wanted to demonstrate what ive attempted :) — Nick Jam, Sep 10 '19 at 12:34
@BalzGuenat our lab professor gave us a hint that we're meant to iterate through the list and then use a sorting API like collections.sort or comparators — Nick Jam, Sep 10 '19 at 12:46

dassum · Answer 1 · 2019-09-10T12:41:32.917

5

try the below code :

billingList.sort(Comparator.comparing(a -> a.getEmail));

edited Sep 10 '19 at 12:41

answered Sep 10 '19 at 12:32

dassum

4,727
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2

I believe that should be `a -> a.getEmail()`. – Balz Guenat Sep 10 '19 at 12:34
1

Maybe you've meant `Collections.sort()` instead? `Billing` doesn't have `sort()` as far as I know. – Amongalen Sep 10 '19 at 12:35
1

Since Java 8 it has. Check [docs](https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#sort-java.util.Comparator-). Because `List` has this method. – Michał Krzywański Sep 10 '19 at 12:38
1

Amongalen meant `billingList.sort` or such. A typo on your side. `billings.sort(Comparator.compairing(Billing::getEmail));` – Joop Eggen Sep 10 '19 at 12:40
Sorry for the confusion I have updated the answer. – dassum Sep 10 '19 at 12:41
1

I believe you could also try: `Comparator.comparing(Billing::getEmail)` – Mr. Polywhirl Sep 10 '19 at 14:49

Fullstack Guy · Answer 2 · 2019-09-10T12:49:23.833

Since the email is a String and also a Comparable you can use the String.compareTo to sort using the email property. (This is a pre Java-8 solution):

public static List<Billing> sortedListByEmail(List<Billing> Billing) {
    List<Billing> sort = new ArrayList<>(Billing);
    Collections.sort(sort, new Comparator<Billing>() {
            public int compare(Billing o1, Billing o2) {
                   return o1.getEmail().compareTo(o2.getEmail());
            }
      }
   );
   return sort;
}

In Java-8 this can be made more compact, with the Comparator#comparing:

public static List<Billing> sortedListByEmail(List<Billing> Billing) {
        List<Billing> sorted = new ArrayList<>(Billing);
        sorted.sort(Comparator.comparing(b -> b.getEmail()));
        return sorted;
}

Here the original list supplied is not sorted in place, instead a copy is made which is sorted.

Or you can use Stream#sorted to do it in an elegant way which will also return you a new List instead of modifying the original one:

public static List<Billing> sortedListByEmail(List<Billing> Billing) {
    return Billing.stream()
                  .sorted(Comparator.comparing(b -> b.getEmail()))
                  .collect(Collectors.toList());
}

score 0 · Answer 3 · answered Sep 10 '19 at 12:54

If you want to do it old ways then got for below code

    public static ArrayList<Billing> sortedListByEmail(ArrayList<Billing> Billing) {

    Collections.sort(Billing, new Comparator<Billing>() {
        public int compare(Billing o1, Billing o2) {
            return o1.getEmail().compareTo(o2.getEmail());
        }
    });

    return Billing;
}

Few things you are doing wrong in your code - First - return o1.getEmail() > o2.getEmail() ? -1 : o1.getEmail().equals(o2.getEmail() ? 0 : 1); you cannot compare a string value like integer value.

Second - You are creating an empty array list and sorting it. It has no elements, it is empty. ArrayList<Billing> Sort = new ArrayList<Billing>(); ........ Collections.sort(Sort, new Comparator<Billing>() {

With java 8 features it can be done in very less line of code as below

billing.sort(Comparator.comparing(b -> b.getEmail()));

score 0 · Answer 4 · answered Sep 10 '19 at 13:04

0

This will change the existing array, no need of new variable,

Collections.sort(billingList, Comparator.comparing(Billing::getEmail));

answered Sep 10 '19 at 13:04

Deepesh kumar Gupta

884
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score 0 · Answer 5 · answered Sep 10 '19 at 13:04

With considering that Billing List object name is billingList

1) If you are using Java 8 you can do it using below approaches:

Using Collections.sort with Lambda expression:

Collections.sort(billingList, (b1, b2) -> b1.getEmail().compareTo(b2.getEmail()));

Using sort method of List Interface (default method)

billingList.sort(Comparator.comparing(Billing::getEmail));

2) If you are using earlier version of Java

Collections.sort(billingList, new Comparator<Billing>() {

      public int compare(final Billing b1, final Billing b2) {

        return b1.getEmail().compareTo(b2.getEmail());

      };
    });

Sort an ArrayList by an object's attribute in java

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