question: public int addTaxon ( Taxon taxon ) { int index = getTaxonIndex ( taxon ) ; if ( index == - 1 ) { taxa . add ( taxon ) ; fireTaxonAdded ( taxon ) ; index = taxa . size ( ) - 1 ; } return index ; }
target:  Adds the given taxon and returns its index. If the taxon is already in the list then it is not added but it returns its index.