Format mac address on EditText ( java )

formatmacaddress.java

txtmacmacaddress.addTextChangedListener(new TextWatcher() {
            String mPreviousMac = null;

            @Override
            public void afterTextChanged(Editable arg0) {
            }

            @Override
            public void beforeTextChanged(CharSequence arg0, int arg1, int arg2, int arg3) {
            }

            @SuppressLint("DefaultLocale")
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                String enteredMac = txtmacmacaddress.getText().toString().toUpperCase();
                String cleanMac = clearNonMacCharacters(enteredMac);
                String formattedMac = formatMacAddress(cleanMac);

                int selectionStart = txtmacmacaddress.getSelectionStart();
                formattedMac = handleColonDeletion(enteredMac, formattedMac, selectionStart);
                int lengthDiff = formattedMac.length() - enteredMac.length();

                setMacEdit(cleanMac, formattedMac, selectionStart, lengthDiff);

            }

            /**
             * Strips all characters from a string except A-F and 0-9.
             * @param mac       User input string.
             * @return          String containing MAC-allowed characters.
             */
            private String clearNonMacCharacters(String mac) {
                return mac.replaceAll("[^A-Fa-f0-9]", "");
            }

            /**
             * Adds a colon character to an unformatted MAC address after
             * every second character (strips full MAC trailing colon)
             * @param cleanMac      Unformatted MAC address.
             * @return              Properly formatted MAC address.
             */
            private String formatMacAddress(String cleanMac) {
                int grouppedCharacters = 0;
                StringBuilder formattedMac = new StringBuilder();

                for (int i = 0; i < cleanMac.length(); ++i) {
                    formattedMac.append(cleanMac.charAt(i));
                    ++grouppedCharacters;

                    if (grouppedCharacters == 2) {
                        formattedMac.append(":");
                        grouppedCharacters = 0;
                    }
                }

                // Removes trailing colon for complete MAC address
                if (cleanMac.length() == 12)
                    formattedMac = new StringBuilder(formattedMac.substring(0, formattedMac.length() - 1));

                return formattedMac.toString();
            }

            /**
             * Upon users colon deletion, deletes MAC character preceding deleted colon as well.
             * @param enteredMac            User input MAC.
             * @param formattedMac          Formatted MAC address.
             * @param selectionStart        MAC EditText field cursor position.
             * @return                      Formatted MAC address.
             */
            private String handleColonDeletion(String enteredMac, String formattedMac, int selectionStart) {
                if (mPreviousMac != null && mPreviousMac.length() > 1) {
                    int previousColonCount = colonCount(mPreviousMac);
                    int currentColonCount = colonCount(enteredMac);

                    if (currentColonCount < previousColonCount) {
                        formattedMac = formattedMac.substring(0, selectionStart - 1) + formattedMac.substring(selectionStart);
                        String cleanMac = clearNonMacCharacters(formattedMac);
                        formattedMac = formatMacAddress(cleanMac);
                    }
                }
                return formattedMac;
            }

            /**
             * Gets MAC address current colon count.
             * @param formattedMac      Formatted MAC address.
             * @return                  Current number of colons in MAC address.
             */
            private int colonCount(String formattedMac) {
                return formattedMac.replaceAll("[^:]", "").length();
            }

            /**
             * Removes TextChange listener, sets MAC EditText field value,
             * sets new cursor position and re-initiates the listener.
             * @param cleanMac          Clean MAC address.
             * @param formattedMac      Formatted MAC address.
             * @param selectionStart    MAC EditText field cursor position.
             * @param lengthDiff        Formatted/Entered MAC number of characters difference.
             */
            private void setMacEdit(String cleanMac, String formattedMac, int selectionStart, int lengthDiff) {
                txtmacmacaddress.removeTextChangedListener(this);
                if (cleanMac.length() <= 12) {
                    txtmacmacaddress.setText(formattedMac);
                    txtmacmacaddress.setSelection(selectionStart + lengthDiff);
                    mPreviousMac = formattedMac;
                    macmask = formattedMac;
                } else {
                    txtmacmacaddress.setText(mPreviousMac);
                    txtmacmacaddress.setSelection(mPreviousMac.length());
                    macmask = mPreviousMac;
                }
                txtmacmacaddress.addTextChangedListener(this);
            }
        });