question: @ Override public V put ( K key , V value ) { if ( key == null ) { return putValueForNullKey ( value ) ; } int hash = secondaryHash ( key ) ; HashMapEntry < K , V > [ ] tab = table ; int index = hash & ( tab . length - 1 ) ; for ( HashMapEntry < K , V > e = tab [ index ] ; e != null ; e = e . next ) { if ( e . hash == hash && key . equals ( e . key ) ) { preModify ( e ) ; V oldValue = e . value ; e . value = value ; return oldValue ; } } modCount ++ ; if ( size ++ > threshold ) { tab = doubleCapacity ( ) ; index = hash & ( tab . length - 1 ) ; } addNewEntry ( key , value , hash , index ) ; return null ; }
target:  Maps the specified key to the specified value.