Как преобразовать BigDecimal в экспоненциальную форму?

Question

Как преобразовать объект BigDecimal в представление строки, которое использует экспоненциальную форму? что-то вроде: 3.134e67? Я просмотрел API и нашел toEngineeringString(), но он не дает мне то, что я хочу.

Answer 1

Вы читали документацию NumberFormat, это от DecimalFormat: См: http://docs.oracle.com/javase/1.4.2/docs/api/java/text/DecimalFormat.html

Scientific Notation

Numbers in scientific notation are expressed as the product of a mantissa and a power of ten, for example, 1234 can be expressed as 1.234 x 10^3. The mantissa is often in the range 1.0 <= x < 10.0, but it need not be. DecimalFormat can be instructed to format and parse scientific notation only via a pattern; there is currently no factory method that creates a scientific notation format. In a pattern, the exponent character immediately followed by one or more digit characters indicates scientific notation. Example: "0.###E0" formats the number 1234 as "1.234E3".

• The number of digit characters after the exponent character gives the minimum exponent digit count. There is no maximum. Negative exponents are formatted using the localized minus sign, not the prefix and suffix from the pattern. This allows patterns such as "0.###E0 m/s".

• The minimum and maximum number of integer digits are interpreted together:

  • If the maximum number of integer digits is greater than their minimum number and greater than 1, it forces the exponent to be a multiple of the maximum number of integer digits, and the minimum number of integer digits to be interpreted as 1. The most common use of this is to generate engineering notation, in which the exponent is a multiple of three, e.g., "##0.#####E0". Using this pattern, the number 12345 formats to "12.345E3", and 123456 formats to "123.456E3".

  • Otherwise, the minimum number of integer digits is achieved by adjusting the exponent. Example: 0.0formatted with "00.###E0" yields "12.3E-4".

• The number of significant digits in the mantissa is the sum of the minimum integer and maximum fraction digits, and is unaffected by the maximum integer digits. For example, 12345 formatted with "##0.##E0" is "12.3E3". To show all digits, set the significant digits count to zero. The number of significant digits does not affect parsing.

• Exponential patterns may not contain grouping separators.

Answer 2

Вы ищете что-то в этом роде?

YY^XX (мод QQ)

int fastMod(int YY, int XX, int QQ){ 
    int ZZ;            //declare variables 
    int RR = 1; 

    while (XX != 0){         //while XX != 0 
     ZZ = XX % 2;         //mod XX by 2 
     XX= XX/2;          //divide XX by 2 
     if (ZZ == 1)         //if ZZ is one 
     RR = (RR * YY) % QQ;       //mod (RR*YY) by QQ 
     YY= (YY * YY) % QQ;        //mod (YY*YY) by QQ  
    } 
    return RR;           //return int 
} 

Когда вы начинаете использовать GIANT номера вам нужно будет использовать модульную арифметику. Это особенно полезно при создании больших простых чисел, как в алгоритме RSA. Основы модулярной арифметики покрыты здесь: http://www.brainjammer.com/math/modular-arithmetic/

Answer 3

ли это поможет?

BigDecimal bd = new BigDecimal(3.134e67); 
String.valueOf(bd.doubleValue())