getRoots() - JPA AbstractQuery's method

Return the query roots. These are the roots that have been defined for the CriteriaQuery or Subquery itself, including any subquery roots defined as a result of correlation. Returns empty set if no roots have been defined. Modifications to the set do not affect the query.
the set of query roots
JPA 2.0

This documentation page is derived (with some adjustments) from the open source JPA 2 RI (EclipseLink)
and is available under the terms of the Eclipse Public License, v. 1.0 and Eclipse Distribution License, v. 1.0.
Object Relational Mapping (ORM) JPA 2 providers include Hibernate, EclipseLink, TopLink, OpenJPA and DataNucleus.
ObjectDB is not an ORM JPA implementation but an Object Database for Java with built in JPA 2 support.