How to use

union

method

in

org.apache.jena.sparql.engine.ref.Evaluator

@Override
public void visit(OpDisjunction opDisjunction)
{
  // Evaluation is as a concatentation of alternatives 
  Table table = TableFactory.createEmpty() ;
  
  for ( Iterator<Op> iter = opDisjunction.iterator() ; iter.hasNext() ; )
  {
    Op op = iter.next() ;
    Table eltTable = eval(op) ;
    table = evaluator.union(table, eltTable) ;
  }
  push(table) ;
}

@Override
public void visit(OpUnion opUnion)
{
  Table left = eval(opUnion.getLeft()) ;
  Table right = eval(opUnion.getRight()) ;
  Table table = evaluator.union(left, right) ;
  push(table) ;
}

  current = stepResult ;
else
  current = evaluator.union(current, stepResult) ;