Remove duplicate objects from a ArrayList in Android

Question

I know this has be discussed over and over again here, but none of the examples I've tried worked for me.

What I've got

I access the Call log from Android and I get a list of all calls made. Of course, here I get a lot of duplicates. First I make a List

List<ContactObject> lstContacts = new ArrayList<ContactObject>();

Then I add objects into it

While (get some record in call log)
{
    ContactObject contact = new ContactObject();
    contact.SetAllProperties(......)  
    lstContacts.add(contact);  
}

Set<ContactObject> unique = new LinkedHashSet<ContactObject>(lstContacts);
lstContacts = new ArrayList<ContactObject>(unique);

The Contact Object class is simple

public class ContactObject {

    public ContactObject() {
        super();
    }

 @Override
 public boolean equals(Object obj) {
     if (!(obj instanceof ContactObject))
        return false;

     return this.lstPhones == ((ContactObject) obj).getLstPhones(); 
 }

 @Override
 public int hashCode() {
     return lstPhones.hashCode();
 }

    private long Id;
    private String name;
    private List<String> lstPhones;  
    private String details;

   //... getters and settres
}

What I need

I need to have a Contact only once in the list. As I've read around here there are a couple of things that can be done like Set, HashSet, TreeSet. TreeSet seems the best as it keeps the order just as I receive it from the Call log. I've tried to make my code work with it but no success. Could anyone be so kind to give me a sample code based on my example. Thank you for your time.

The Working Solution. Thank you all for your support, you've made my day.

In ContactObject override the two methods

 @Override
     public boolean equals(Object obj) {
         if (!(obj instanceof ContactObject))
            return false;

         return lstPhones.equals(((ContactObject) obj).getLstPhones());
     }

     @Override
     public int hashCode() {
         return (lstPhones == null) ? 0 : lstPhones.hashCode();
     }

//Getters and Setters and COnstructor....

Simply use it as

Set<ContactObject> unique = new LinkedHashSet<ContactObject>(lstContacts);
lstContacts = new ArrayList<ContactObject>(unique);

Answer 1

LinkedHashSet which keeps insertion-order can be used in your case.

HashSet: no order.

TreeSet: sorted set, but not keep insertion order.

EDIT: As Software Monkey commented, hashCode() and equals() should be overwritten in ContactObject to fit the hash-based Set.

Answer 2

Remove duplication of Custom Object

Example of Removing duplicate using Comparator

Lets suppose you have a class "Contact"

public class Contact implements Comparable<Contact> {


public String getName() {
    return this.Name;
}

public void setName(String name) {
    this.Name = name;
}

public String getNumber() {
    return this.Number;
}

public void setNumber(String number) {
    this.Number = number;
}


 ///// this method is very important you must have to implement it.
@Override
public String toString() {
    return "\n" +"Name=" + name + "   Number=" + Number;
}

Here is how you can remove duplicate entries using Set , just pass your list in the function and it will work for you. New list will be returned which will have no duplicated contacts.

 public ArrayList<Contact>  removeDuplicates(ArrayList<Contact> list){
    Set<Contact> set = new TreeSet(new Comparator<Contact>() {

        @Override
        public int compare(Contact o1, Contact o2) {
            if(o1.getNumber().equalsIgnoreCase(o2.getNumber())){
                return 0;
            }
            return 1;
        }
    });
    set.addAll(list);

    final ArrayList newList = new ArrayList(set);
    return newList;
}

It worked for me so please try and give me your feedback. Thanks

P.S: Credit goes to Nilanchala at this article