question: public < T extends DataObject > Joiner join ( Class < T > clazz , String alias ) { if ( ! jClasses . isEmpty ( ) ) { throw new JoinerException ( "Illegal use of Joiner; starting a new join in the middle of a join chain" ) ; } JClass jc = new JClass ( clazz , alias , jClasses . size ( ) ) ; jClasses . add ( jc ) ; lastJClass = jc ; aliasMap . put ( alias , jc ) ; return this ; }
target:  Starts a new query not related to a previous class query.