Default precision is 7 instead of 13 ? about evalex

[squeek502]

The precision of 7 comes from using MathContext.DECIMAL32 by default (see Java docs).

As for why that's the default, I'm not sure.

[squeek502]

Looked into this a bit more. The 13 precision you are seeing in your default BigDecimal is not actually a default precision; precision adapts to the number of digits when it's not specified.

Looking at the BigDecimal source code:

precision field:

private volatile transient int precision = 0;

precision method:

    /**
     * Returns the <i>precision</i> of this {@code BigDecimal}.  (The
     * precision is the number of digits in the unscaled value.)
     *
     * <p>The precision of a zero value is 1.
     *
     * @return the precision of this {@code BigDecimal}.
     * @since  1.5
     */
    public int precision() {
        int result = precision;
        if (result == 0) {
            result = digitLength();
            precision = result;
        }
        return result;
    }

If I'm correct, then this should be true:

   BigDecimal bd = new BigDecimal("123");
   System.out.println(bd.precision());    // print 3

And if that's true, then it looks like MathContext.UNLIMITED would be the 'correct' default in order to match default BigDecimal behavior.

[uklimaschewski]

Exactly, @squeek502. There is no default MathContext in Java, so I had to choose one specific. DECIMAL32 won the race. I think there was some reason after some tests, but I'm not sure.
Just read your second commen, @squeek502 and that may have been one reason.
Probably a separate constructor Expression(String expression, MathContext context) could give more flexibility.

[s101d1]

Hi all, thanks for the clarification. I guess for now I will set the precision to 0 and rounding mode to HALF_UP to match the default behavior (UNLIMITED).