question: static public String doubleToString ( double d ) { if ( Double . isInfinite ( d ) || Double . isNaN ( d ) ) { return "null" ; } String s = Double . toString ( d ) ; if ( s . indexOf ( '.' ) > 0 && s . indexOf ( 'e' ) < 0 && s . indexOf ( 'E' ) < 0 ) { while ( s . endsWith ( "0" ) ) { s = s . substring ( 0 , s . length ( ) - 1 ) ; } if ( s . endsWith ( "." ) ) { s = s . substring ( 0 , s . length ( ) - 1 ) ; } } return s ; }
target:  Produce a string from a double. The string "null" will be returned if the number is not finite.