Review

class AttributeSource {
  /**
   * Captures the state of all Attributes. The return value can be passed to
   * {@link #restoreState} to restore the state of this or another AttributeSource.
   */
  public State captureState() {
    if (!hasAttributes()) {
      return null;
    }
      
    if (currentState == null) {
      computeCurrentState();
    }
    return (State) this.currentState.clone();
  }

}