org.zkoss.poi.ss.util

Class NumberComparer

java.lang.Object

org.zkoss.poi.ss.util.NumberComparer

public final class NumberComparer
extends java.lang.Object

Excel compares numbers using different rules to those of java, so Double.compare(double, double) won't do.

Author:

Josh Micich

Constructor Summary

Constructors

Constructor and Description
NumberComparer()

Method Summary

Modifier and Type	Method and Description
static int	compare(double a, double b) This class attempts to reproduce Excel's behaviour for comparing numbers.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

NumberComparer

public NumberComparer()

Method Detail

compare

public static int compare(double a,
                          double b)

This class attempts to reproduce Excel's behaviour for comparing numbers. Results are mostly the same as those from Double.compare(double, double) but with some rounding. For numbers that are very close, this code converts to a format having 15 decimal digits of precision and a decimal exponent, before completing the comparison.

In Excel formula evaluation, expressions like "(0.06-0.01)=0.05" evaluate to "TRUE" even though the equivalent java expression is false. In examples like this, Excel achieves the effect by having additional logic for comparison operations.

Note - Excel also gives special treatment to expressions like "0.06-0.01-0.05" which evaluates to "0" (in java, rounding anomalies give a result of 6.9E-18). The special behaviour here is for different reasons to the example above: If the last operator in a cell formula is '+' or '-' and the result is less than 2⁵⁰ times smaller than first operand, the result is rounded to zero. Needless to say, the two rules are not consistent and it is relatively easy to find examples that satisfy
"A=B" is "TRUE" but "A-B" is not "0"
and
"A=B" is "FALSE" but "A-B" is "0"

This rule (for rounding the result of a final addition or subtraction), has not been implemented in POI (as of Jul-2009).

Returns:

negative, 0, or positive according to the standard Excel comparison of values a and b.