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

edittext.addTextChangedListener(new TextWatcher() {
  @Override
  public void onTextChanged(CharSequence s, int start, int before, int count) {
    if (edittext.getText().toString().length() == 4) {
      edittext.append(" ");
    }
  }
  @Override
  public void afterTextChanged(Editable s) {
  }
  @Override
  public void beforeTextChanged(CharSequence s, int start, int count, int after) {
  }
});