Android EditText credit card formatting (mask)

activity_some.xml

<EditText
  android:id="@+id/creditCard"
  android:inputType="number"
  android:digits=" 1234567890"
  android:maxLength="22"
/>

SomeActivity.java

package com.company;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;


public class SomeActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_some);
        
        EditText creditCard = (EditText) findViewById(R.id.creditCard);
        creditCard.addTextChangedListener(new CreditCardNumberFormattingTextWatcher());
    }

  /**
   * Formatting a credit card number: #### #### #### #######
   */
  public static class CreditCardNumberFormattingTextWatcher implements TextWatcher {
  
      private boolean lock;
  
      @Override
      public void onTextChanged(CharSequence s, int start, int before, int count) {
      }
  
      @Override
      public void beforeTextChanged(CharSequence s, int start, int count, int after) {
      }
  
      @Override
      public void afterTextChanged(Editable s) {
          if (lock || s.length() > 16) {
              return;
          }
          lock = true;
          for (int i = 4; i < s.length(); i += 5) {
              if (s.toString().charAt(i) != ' ') {
                  s.insert(i, " ");
              }
          }
          lock = false;
      }
}