question: private Iterator < BindingSet > joinBindingSetEntry ( Map . Entry < String , BindingSet > entry ) { List < Collection < BindingSet > > matches = new ArrayList < > ( ) ; if ( type == HashJoinType . CONSTANT_JOIN_VAR ) { if ( bindingJoinVarHash . containsKey ( entry . getKey ( ) ) ) { matches . add ( bindingJoinVarHash . get ( entry . getKey ( ) ) ) ; } } else { List < String > valOrders = getValueOrders ( entry . getKey ( ) ) ; for ( String s : valOrders ) { if ( bindingJoinVarHash . containsKey ( s ) ) { matches . add ( bindingJoinVarHash . get ( s ) ) ; } } } if ( matches . size ( ) == 0 ) { return Collections . emptyIterator ( ) ; } else { return new BindingSetCollectionsJoinIterator ( entry . getValue ( ) , matches ) ; } }
target:  This method returns an Iterator which joins the given Entry's BindingSet to all BindingSets which matching the Entry's key.