Intermittently mutable data concept

Index.java

public interface Index() {
  /*
   * @return mutable copy of indexes contained in this instance.
   */
  MutableIndex beginMutation();

  /*
   * Example usage of indexes for data retrieval.
   */
  PrimaryKey findBySomeAttributeValue(String value);
  PrimaryKey findByOtherAttributeValue(String value);
  /*...*/
}

MutableIndex.java

/*
 * This class is not thread safe, it is intended to exist only
 * in one thread for a short period of time (equivalent of one transaction).
 * #endMutation has to be called before sharing data with others.
 */
public interface MutableIndex extends Index {
  /*
   * @return immutable copy of indexes contained in this instance.
   */
  Index endMutation();
  
  /*
   * Example mutable update of contained indexes.
   */
  void updateSomeIndexes(SomeDomainObject dto);
  void updateOtherIndexes(OtherDomainObject dto);
  /*...*/
}