Java IO.pdf - Nguyen Dang Binh

}
Java I/O
/**
* Overrides hashCode
*/
public int hashCode() {
return super.hashCode() * 31 + parser.getNegativePrefix().hashCode();
}
Aside from special cases like Inf and NaN, the big trick in formatting both longs and doubles
is to separate the mantissa from the exponent. The mantissa is the set of digits that comes
before the E. For example, in 6.0220943E+23 the mantissa is 6.0220943. (Technically, the
mantissa is 60220943 without a decimal point, but for reasons you'll see shortly, I need to
hang onto it.) By separating the mantissa from the exponent, we can format each one
separately, then concatenate them together with an "E" in between. The problem is that Java
doesn't have any real concept of mantissa or exponent, especially in base 10. We find the
exponent by taking the log10 of the number and rounding toward zero to the nearest integer.
(Math.floor(Math.log(number) / Math.log(10))). Dividing the loose line number by
Math.pow(10, exponent), we get a mantissa between 1 and 9.999999999.
For true scientific notation, this is exactly what you want. However, this program is a little
more general and allows programmers to choose to format numbers as 13.24E+12 instead of
the equivalent 1.324E+13. Therefore, if the programmer sets the minimum integer digits
higher than 1, we shift the mantissa to the left (multiply by 10) and subtract 1 from the
exponent for each shift. In exponential notation, unlike regular decimal notation, a minimum
number of integer digits greater than the available number of integer digits does not lead to
insignificant zeros.
Parsing is easier. All we have to do is read the exponential string, like 6.345E-1, twice. The
first time you read, you get the mantissa (6.345). The parse() method automatically stops
when it encounters the nonnumeric character E. Advance the parse position one space to skip
past the E and read the exponent. Then multiply the mantissa by Math.pow(10, exponent),
convert that into a Double object, and return it. If there's a problem parsing the exponent, then
we reset parsePosition back to its original value and return null.
By the way, in case you were wondering, the fourth official language of Switzerland is
Romansh, also known as Rhaeto-Romanic. Romansh is spoken by about 1.5% of
Switzerland's population and survives the onslaught of German/French/English/Italian by
virtue of being prevalent in many isolated mountain communities in the Alps.
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