question: public int hashCode ( ) { int hashCode = this . hashCode ; if ( hashCode == 0 ) { hashCode = ( ( groupId . hashCode ( ) * 19 + artifactId . hashCode ( ) ) * 19 + version . hashCode ( ) ) * 19 + classifier . hashCode ( ) ; if ( hashCode == 0 ) { hashCode = - 1 ; } this . hashCode = hashCode ; } return hashCode ; }
target:  Get the hash code.