Re: [rules-users] [rules user] different behavior on double type
4.0.7 is rather old. 5.1.1 and later do not exhibit this behaviour.
However, it should be noted that comparing double values using == is a
precarious approach. For instance, 99.9 (the mathematical number)
cannot be represented as a double machine number. Hence, you do not
truly test for
equality with that number, just with its approximation by some machine
number.
-W
On 26/03/2012, Zeke <xanadu860122(a)gmail.com> wrote:
Hi, guys:
I am using Drools 4.0.7. I find a strange behavior. When my LHS is
"Message( varDouble == 99.9 )" and "varDouble" equals "new
Double(99.9)",
the condition is true. But when my LHS is "Message( types.doubleType ==
99.9 )" and the "doubleType" field is also equal to "new
Double(99.9)", the
condition is false. I debug the code, and find that:
When the LHS is "Message( varDouble == 99.9 )", the logic will handle the
literal 99.9 as *Double.valueOf( “99.9” )*, and the comparison is between
*(new
Double(99.9)).doubleValue(*) and *Double.valueOf( “99.9” ).doubleValue()*,
When the LHS is "Message( types.doubleType == 99.9 )", the logic is
different from above. The comparison is between *new BigDecimal((Double)
99.9, MathContext.DECIMAL64)* (which double value is 99.90000000000001) and
*new BigDecimal(“99.9”, MathContext.DECIMAL64)* (which double value is
99.9).
I think we need make things consistent. "varDouble" and
"types.doubleType" are of the same type and value. It doesn't make sense
to
have different behavior just because of one field is nesting while the
other is not. I know Drools is using MVEL to evaluate the condition. But I
am not sure it is a MVEL bug or Drools uses MVEL wrong. It will be much
appreciated if you can give me any comments!