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

public class EditTextActivity extends AppCompatActivity {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EditText edittext = findViewById(R.id.edittext);
        edittext.addTextChangedListener(new TextWatcher() {
            @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) {
                if (s.length()==4){
                    s.append(" ");
                }
            }
        });
    }
}