Why is BigDecimal.equals specified to compare both value and scale individually?
This is not a question about how to compare two BigDecimal objects - I know that you can use compareTo instead of equals to do that, since equals is documented as:
Unlike compareTo, this method considers two BigDecimal objects equal only if they are equal in value and scale (thus 2.0 is not equal to 2.00 when compared by this method).
The question is: why has the equals been specified in this seemingly counter-intuitive manner? That is, why is it important to be able to distinguish between 2.0 and 2.00?
It seems likely that there must be a reason for this, since the Comparable documentation, which specifies the compareTo method, states:
It is strongly recommended (though not required) that natural orderings be consistent with equals
I imagine there must be a good reason for ignoring this recommendation.
Answer
Because in some situations, an indication of precision (i.e. the margin of error) may be important.
For example, if you're storing measurements made by two physical sensors, perhaps one is 10x more precise than the other. It may be important to represent this fact.