double类型精度问题格式设置

我们知道double类型在进行处理时会涉及到精度丢失问题比如

double d=100*1.005;

结果d的结果为100.49999999999999

怎么解决这种问题呢，用DecimalFormat，它对double类型的进行四舍五入处理用法如下：

DecimalFormat df=new DecimalFormat(pattern); 

String nums=df.format(value);

这里给pattern：”.00“

value:100*1.005

nums值为：100.50 

pattern常用的千分号显示：#,##0.00 (为什么个位数用0不用#，因为如果df.format(0)，用#的话0显示为空，结果为.00而用0的话显示0.00)

pattern设置可以参考下面：

Symbol Location Localized? Meaning

0 Number Yes Digit

# Number Yes Digit, zero shows as absent

. Number Yes Decimal separator or monetary decimal separator

- Number Yes Minus sign

, Number Yes Grouping separator

E Number Yes Separates mantissa and exponent in scientific notation. Need not be quoted in prefix or suffix.

; Subpattern boundary Yes Separates positive and negative subpatterns

% Prefix or suffix Yes Multiply by 100 and show as percentage

\u2030 Prefix or suffix Yes Multiply by 1000 and show as per mille

¤(\u00A4) Prefix or suffix No Currency sign, replaced by currency symbol. If doubled, replaced by international currency symbol. If present in a pattern, the monetary decimal separator is used instead of the decimal separator.

' Prefix or suffix No Used to quote special characters in a prefix or suffix, for example, "'#'#" formats 123 to "#123". To create a single quote itself, use two in a row: "# o''clock".