HashSet adding duplicate Strings

Question

I am trying to get unique phone numbers from the contact provider in android and I am using a HashSet to add the different phone numbers of a contact

   Set<String> newNumbers = new HashSet<>();

   while(findNumbers.moveToNext()){
      String phone = findNumbers.getString(0);
      phone = phone.replaceAll("[\\s\\-()]", ""); 
      boolean isNumberAdded = newNumbers.add(phone);
      if(isNumberAdded){
         Log.d(TAG,"Phone= " + phone);
       }else{
         Log.d(TAG,"Rejected Phone= " + phone);
         continue;
        }
    }

However this happens:

1. Phone= 0502809903
2. Phone= ‪+971556072980‬
3. Rejected Phone= ‪+971556072980‬ <- rejected duplicate
4. Phone= +971552767944
5. Phone= +971556072980 <-- accepted duplicate

EDIT: If the Strings are created like this, it works however the strings that I get from the cursor does not.

    ArrayList<String> testing = new ArrayList<String>();
    testing.add("0502809903");
    testing.add("+971556072980");
    testing.add("+971556072980");
    testing.add("+971552767944");
    testing.add("+971556072980");

    Set<String> numbers = new HashSet<>();
    for(String data: testing){

        boolean isNumberAdded = numbers.add(data);
        if(isNumberAdded){
            Log.d("Test","Accepted " + data);
        }else{
            Log.d("Test","Rejected " + data);
        }
    }

Edit2: displayed the numbers as char arrays, How do I fix it?

1. Original = [0, 5, 0, 2, 8, 0, 9, 9, 0, 3]
2. Accepted Phone= 0502809903
3. Original = [‪, +, 9, 7, 1, 5, 5, 6, 0, 7, 2, 9, 8, 0, ‬]
4. Accepted Phone= ‪+971556072980‬
5. Original = [‪, +, 9, 7, 1, 5, 5, 6, 0, 7, 2, 9, 8, 0, ‬]
6. Rejected Phone= ‪+971556072980‬
7. Original = [+, 9, 7, 1, 5, 5, 2, 7, 6, 7, 9, 4, 4]
8. Accepted Phone= +971552767944
9. Original = [+, 9, 7, 1, 5, 5, 6, 0, 7, 2, 9, 8, 0]
10. Accepted Phone= +971556072980

Answer 1

You have garbage in your strings. Try this:

boolean isNumberAdded = newNumbers.add(phone.trim());

This should do the trick.

EDIT: Or maybe it doesn't... According to this question, if you want to remove non-printable characters, you should use the following:

boolean isNumberAdded = newNumbers.add(phone.replaceAll("\\p{C}", ""));

Let me know if it works this time.

Answer 2

HashSet will use GetHashCode and Equals to determine equality of your objects. Right now, since you're not overriding these methods , the default System.Object's reference equality will be used. Each time you add a new value, it's a unique object instance, so the HashSet sees it as a unique object.

you will need to override hashcode and equal.

Why is it important to override GetHashCode when Equals method is overridden?