Even-though It's late. Intended for future visitors.

Fetures of the following codes

1. Puts thousand separator in EditText as it's text changes.

2. adds 0. Automatically when pressed period (.) At First.

3. Ignores 0 input at Beginning.

Just copy the following Class named

NumberTextWatcherForThousand which implements TextWatcher

import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import java.util.StringTokenizer;

/**
 * Created by skb on 12/14/2015.
 */
public class NumberTextWatcherForThousand implements TextWatcher {

    EditText editText;


    public NumberTextWatcherForThousand(EditText editText) {
        this.editText = editText;


    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {

    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {

    }

    @Override
    public void afterTextChanged(Editable s) {
        try
        {
            editText.removeTextChangedListener(this);
            String value = editText.getText().toString();


            if (value != null && !value.equals(""))
            {

                if(value.startsWith(".")){
                    editText.setText("0.");
                }
                if(value.startsWith("0") && !value.startsWith("0.")){
                    editText.setText("");

                }


                String str = editText.getText().toString().replaceAll(",", "");
                if (!value.equals(""))
                editText.setText(getDecimalFormattedString(str));
                editText.setSelection(editText.getText().toString().length());
            }
            editText.addTextChangedListener(this);
            return;
        }
        catch (Exception ex)
        {
            ex.printStackTrace();
            editText.addTextChangedListener(this);
        }

    }

    public static String getDecimalFormattedString(String value)
    {
        StringTokenizer lst = new StringTokenizer(value, ".");
        String str1 = value;
        String str2 = "";
        if (lst.countTokens() > 1)
        {
            str1 = lst.nextToken();
            str2 = lst.nextToken();
        }
        String str3 = "";
        int i = 0;
        int j = -1 + str1.length();
        if (str1.charAt( -1 + str1.length()) == '.')
        {
            j--;
            str3 = ".";
        }
        for (int k = j;; k--)
        {
            if (k < 0)
            {
                if (str2.length() > 0)
                    str3 = str3 + "." + str2;
                return str3;
            }
            if (i == 3)
            {
                str3 = "," + str3;
                i = 0;
            }
            str3 = str1.charAt(k) + str3;
            i++;
        }

    }

    public static String trimCommaOfString(String string) {
//        String returnString;
        if(string.contains(",")){
            return string.replace(",","");}
        else {
            return string;
        }

    }
}

Use This Class on your EditText as follows

editText.addTextChangedListener(new NumberTextWatcherForThousand(editText));

To get the input as plain Double Text

Use the trimCommaOfString method of the same class like this

NumberTextWatcherForThousand.trimCommaOfString(editText.getText().toString())

Git

I will not discuss if it's re-inventing some wheel, but comment on the two code versions given.

Recursive version

The loop

    do {
        number = number % 1000;
    } while (number > 999);

is nonsense. number % 1000 can never be > 999, so number = number % 1000; without the loop does exactly the same.

In the "loop", re-assigning a new value to the method call parameter number is considered bad style. You should introduce a new variable, e.g. int remainder = number % 1000;.

You can avoid the error-prone handling of the positive flag by utilising recursion as well:

if (number < 0) {
    return "-" + intToThousandSpacedStringOS(-number);
}

You declare your variables very early, and later change their values from an (often useless) initial value to something useful, e.g.

String t = "";

Better declare your variables in the exact same line where you know their value. Or at least, don't assign an initial value, then the compiler gives you an error message if in some execution path you forgot to assign a useful value.

To sum it up, my recursive version would read

public static String intToThousandSpacedStringOS(int number) {
    if (number < 0) {
        return "-" + intToThousandSpacedStringOS(-number);
    } else if (number > 999) {
        return intToThousandSpacedStringOS(number / 1000) + 
               String.format(" %03d", number % 1000); // note the space in the format string.
    } else {
        return String.format("%d", number);
    }
}

Iterative version

Reading and understanding this version is a challenge, and that's a red flag. Don't expect any fellow programmer (and your future self next month) to understand what a line like

r = t.substring(t.length() - 3 * i > 3 ? t.length() - 3 * (i + 1) : 0, t.length() - 3 * i) + " " + r;

does. I guess you cut a chunk out of the original decimal string and prepend that, together with a space, to the result string. Then, at least introduce two variables like

int chunkStart = t.length() - 3 * i > 3 ? t.length() - 3 * (i + 1) : 0;
int chunkEnd = t.length() - 3 * i;
r = t.substring(chunkStart, chunkEnd) + " " + r;

With the ternary-operator conditional, you probably want to avoid a negative chunkStart. I'd write

int chunkStart = Math.max(t.length() - 3 * (i + 1), 0);
int chunkEnd = t.length() - 3 * i;
r = t.substring(chunkStart, chunkEnd) + " " + r;

or

int chunkStart = t.length() - 3 * (i + 1);
if (chunkStart < 0) chunkStart = 0;
int chunkEnd = t.length() - 3 * i;
r = t.substring(chunkStart, chunkEnd) + " " + r;

You seem to love while loops. Typically, for loops are much more readable, as they combine all loop aspects in a single line - your while loop spreads its aspects over half of the method length:

• The initial value is found in line 12: int i = 1;.
• The condition is in line 20: while (t.length() > 3 * i) {.
• The updating is in line 22: i++;.

The variable i that you use in the loop is only loosely related to the values you need inside the loop. You want to iterate a position inside the string backwards from the end, in 3-character steps. A straightforward loop would be e.g.

for (int chunkEnd = t.length() - 3; chunkEnd > 0; chunkEnd -= 3) {
    ...
}

You could use DecimalFormat and just format the number

DecimalFormat formatter = new DecimalFormat("#,###,###");
String yourFormattedString = formatter.format(100000);

The result will be

• 1,000,000 for 1000000
• 10,000 for 10000
• 1,000 for 1000

Update 12/02/2019

This String.format("%,d", number) would be a better(less hardcoded) solution as indicated in the comments below by @DreaminginCode so I thought I would add it here as an alternative

You can use

String value=String.format("%,.2f", num );

to parse the number to String with a thousands separator and then set the result to the TextView or EditText that you want

For example :

txt.setText(String.format("%,.2f", num ));
edt.setText(String.format("%,.2f", num ));