question: public Builder appendQueryParameter ( String key , String value ) { this . opaquePart = null ; String encodedParameter = encode ( key , null ) + "=" + encode ( value , null ) ; if ( query == null ) { query = Part . fromEncoded ( encodedParameter ) ; return this ; } String oldQuery = query . getEncoded ( ) ; if ( oldQuery == null || oldQuery . length ( ) == 0 ) { query = Part . fromEncoded ( encodedParameter ) ; } else { query = Part . fromEncoded ( oldQuery + "&" + encodedParameter ) ; } return this ; }
target:  Encodes the key and value and then appends the parameter to the query string.