Cada vez que escriba en un EditText 4 caracteres se ponga un espacio

private void setTextWatcher(EditText editText) {
  editText.addTextChangedListener(new TextWatcher() {

    @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 (s.length() == 4) {
        editText.setText(s + ' ');
        editText.setSelection(editText.getText().length());
      }
    }
  });
}