Question

How to convert BigDecimal object to a String representation that uses the exponential form? something like: 3.134e67? I looked into the API and I found toEngineeringString() but it does not give me what I want.

Answer 1

Have you read the NumberFormat documentation, this is from DecimalFormat:
See: 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: 0.00123 formatted 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.