# Bigdecimal problem

Discussion in 'Java' started by manzur, Jun 6, 2006.

1. ### manzurGuest

BigDecimal bigDecimal = new BigDecimal("1.00");
BigDecimal bigDecima2 = new BigDecimal("1");

System.out.println(bigDecimal.equals(bigDecima2));

The above gives me false.

Wht should i do to make it print true with out disturbing my already
created bigdecimals.
Bcoz i feel that 1.0,1.00,1,1.0000 are same

manzur, Jun 6, 2006

2. ### Oliver WongGuest

"manzur" <> wrote in message
news:...
> BigDecimal bigDecimal = new BigDecimal("1.00");
> BigDecimal bigDecima2 = new BigDecimal("1");
>
> System.out.println(bigDecimal.equals(bigDecima2));
>
> The above gives me false.
>
> Wht should i do to make it print true with out disturbing my already
> created bigdecimals.
> Bcoz i feel that 1.0,1.00,1,1.0000 are same

http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html

They explicitly tell you that equals will return false when comparing
2.0 to 2.00. They also explain how to get the results you want.

Why would the behaviour of 2.0 != 2.00 be useful? Perhaps for
scientific/engineering applications where significant digits are meaningful.

- Oliver

Oliver Wong, Jun 6, 2006

3. ### manzurGuest

Re: Bigdecimal problem

Oliver Wong wrote:
> "manzur" <> wrote in message
> news:...
> > BigDecimal bigDecimal = new BigDecimal("1.00");
> > BigDecimal bigDecima2 = new BigDecimal("1");
> >
> > System.out.println(bigDecimal.equals(bigDecima2));
> >
> > The above gives me false.
> >
> > Wht should i do to make it print true with out disturbing my already
> > created bigdecimals.
> > Bcoz i feel that 1.0,1.00,1,1.0000 are same

>
> http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html
>
> They explicitly tell you that equals will return false when comparing
> 2.0 to 2.00. They also explain how to get the results you want.
>
> Why would the behaviour of 2.0 != 2.00 be useful? Perhaps for
> scientific/engineering applications where significant digits are meaningful.
>
> - Oliver

iam developing some banking applications where i need to show that 1.0
,1.00,1.000 are same

manzur, Jun 6, 2006
4. ### jhrGuest

Re: Bigdecimal problem

manzur wrote:
> Oliver Wong wrote:
> > "manzur" <> wrote in message
> > news:...
> > > BigDecimal bigDecimal = new BigDecimal("1.00");
> > > BigDecimal bigDecima2 = new BigDecimal("1");
> > >
> > > System.out.println(bigDecimal.equals(bigDecima2));
> > >
> > > The above gives me false.
> > >
> > > Wht should i do to make it print true with out disturbing my already
> > > created bigdecimals.
> > > Bcoz i feel that 1.0,1.00,1,1.0000 are same

> >
> > http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html
> >
> > They explicitly tell you that equals will return false when comparing
> > 2.0 to 2.00. They also explain how to get the results you want.
> >
> > Why would the behaviour of 2.0 != 2.00 be useful? Perhaps for
> > scientific/engineering applications where significant digits are meaningful.
> >
> > - Oliver

>
>
> iam developing some banking applications where i need to show that 1.0
> ,1.00,1.000 are same

Try:

if (bigDecimal.compareTo(bigDecima2) == 0)
{
// code for equals == true
}

jhr, Jun 6, 2006
5. ### Patricia ShanahanGuest

Oliver Wong wrote:
> "manzur" <> wrote in message
> news:...
>> BigDecimal bigDecimal = new BigDecimal("1.00");
>> BigDecimal bigDecima2 = new BigDecimal("1");
>>
>> System.out.println(bigDecimal.equals(bigDecima2));
>>
>> The above gives me false.
>>
>> Wht should i do to make it print true with out disturbing my already
>> created bigdecimals.
>> Bcoz i feel that 1.0,1.00,1,1.0000 are same

>
> http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html
>
> They explicitly tell you that equals will return false when comparing
> 2.0 to 2.00. They also explain how to get the results you want.
>
> Why would the behaviour of 2.0 != 2.00 be useful? Perhaps for
> scientific/engineering applications where significant digits are
> meaningful.
>
> - Oliver

At a more basic level, the result of some operations involving a
BigDecimal depend on its scale. toString gives different answers. The
precision is different. Rounded divisions give different answers.

They are just not equivalent objects.

Patricia

Patricia Shanahan, Jun 6, 2006
6. ### Ingo R. HomannGuest

Hi,

Patricia Shanahan wrote:
>>> BigDecimal bigDecimal = new BigDecimal("1.00");
>>> BigDecimal bigDecima2 = new BigDecimal("1");
>>>
>>> System.out.println(bigDecimal.equals(bigDecima2));
>>>

>
> At a more basic level, the result of some operations involving a
> BigDecimal depend on its scale. toString gives different answers. The
> precision is different. Rounded divisions give different answers.

I understand that, but I think that is not a reason that "1.0" and
"1.00" should not be equal. I mean, especially...

> They are just not equivalent objects.

....that is (IMHO) not correct: "equivalent" - the same word as in
Germany (although we use the strange "Umlaut" "ä" at the beginning) -
which (AFAIK) comes from the Latin words for "equal" and "value", and I
think, the values of "1.00" and "1.0" *are* the same.

Ciao,
Ingo

Ingo R. Homann, Jun 7, 2006
7. ### Oliver WongGuest

"Ingo R. Homann" <> wrote in message
news:4486c9a7\$0\$11077\$-online.net...
> Hi,
>
> Patricia Shanahan wrote:
>>>> BigDecimal bigDecimal = new BigDecimal("1.00");
>>>> BigDecimal bigDecima2 = new BigDecimal("1");
>>>>
>>>> System.out.println(bigDecimal.equals(bigDecima2));
>>>>

>>
>> At a more basic level, the result of some operations involving a
>> BigDecimal depend on its scale. toString gives different answers. The
>> precision is different. Rounded divisions give different answers.

>
> I understand that, but I think that is not a reason that "1.0" and "1.00"
> should not be equal. I mean, especially...
>
>> They are just not equivalent objects.

>
> ...that is (IMHO) not correct: "equivalent" - the same word as in Germany
> (although we use the strange "Umlaut" "ä" at the beginning) - which
> (AFAIK) comes from the Latin words for "equal" and "value", and I think,
> the values of "1.00" and "1.0" *are* the same.

As I've mentioned elsewhere in this newsgroup (but not within this
thread), the concept of equality is context dependent. Are "1.00" and "1.0"
equal? Perhaps yes, if you're talking about pure mathematical numbers.
Perhaps no, if you're talking about engineering measurements with specific
tolerance levels [*]. Definitely not, if you're talking about Strings.

The Java API was designed so that you could provide a comparator object,
so that you could using different metrics for determining how two objects
compare, depending on which metric you're interested in. I thought it might
be a good idea if they did the same thing for the equals method (so you
could provide a custom object to determine whether two objects are equal,
depending on the context). Unfortunately, the API wasn't designed that way.

But moving away from idle daydreaming and coming back to practical
matters: recall that in Java, you're free to implement the equals() method
any way you want, as long as some basic requirements (reflexivity,
transitivity, etc.) are met. The people who designed the BigDecimal class
decided to design it in that particular way. Anyway, it's not like you can't
get the above mentioned desired behaviour: All you have to do is use
compareTo().

- Oliver

[*] An engineer might reject a part that measures "1.0 mm", requiring one
that measures "1.00 mm". Why? Because that engineer might know that if the
part actually measures 1.01 mm (which is considered to be a "1.0 mm" part,
but not a "1.00 mm" part), the device will fail and/or break, whereas if the
device measures 1.004 mm (which is both a "1.0 mm" and "1.00 mm" part), the
device will tolerate this small deviancy, and continue functioning.

Oliver Wong, Jun 7, 2006
8. ### Patricia ShanahanGuest

Ingo R. Homann wrote:
> Hi,
>
> Patricia Shanahan wrote:
>>>> BigDecimal bigDecimal = new BigDecimal("1.00");
>>>> BigDecimal bigDecima2 = new BigDecimal("1");
>>>>
>>>> System.out.println(bigDecimal.equals(bigDecima2));
>>>>

>>
>> At a more basic level, the result of some operations involving a
>> BigDecimal depend on its scale. toString gives different answers. The
>> precision is different. Rounded divisions give different answers.

>
> I understand that, but I think that is not a reason that "1.0" and
> "1.00" should not be equal. I mean, especially...
>
>> They are just not equivalent objects.

>
> ...that is (IMHO) not correct: "equivalent" - the same word as in
> Germany (although we use the strange "Umlaut" "ä" at the beginning) -
> which (AFAIK) comes from the Latin words for "equal" and "value", and I
> think, the values of "1.00" and "1.0" *are* the same.
>
> Ciao,
> Ingo
>

Anyone who thinks they are equivalent objects, try running this:

import java.math.BigDecimal;
public class TestBigDecimal {
public static void main(String[] args) {
System.out.println(new BigDecimal("1.0").
divide(new BigDecimal(3),BigDecimal.ROUND_HALF_EVEN));
System.out.println(new BigDecimal("1.00").
divide(new BigDecimal(3),BigDecimal.ROUND_HALF_EVEN));
}
}

If they really were equivalent, I would expect them to do the same for
anything other than the identity related operations, == comparison and
System.identityHashCode().

A BigDecimal has both a decimal value and a scale, not just a decimal
value. The scale affects some operations, such as the rounded divisions
in the example program.

Their decimal values are equal, and decimal value is the natural
ordering, so it makes sense for compareTo to treat them as equal.

Patricia

Patricia Shanahan, Jun 7, 2006
9. ### Thomas WeidenfellerGuest

Ingo R. Homann wrote:
> I
> think, the values of "1.00" and "1.0" *are* the same.

Not if you are an engineer. 1.00 indicates a higher precision than 1.0.
Depending on the type of rounding used (AFAIK varies in different
countries in engineering), the above numbers e.g. indicate the two
different ranges

1.00: [0.995, 1.005)
1.0: [0.95, 1.05)

for an engineer. And these ranges are rather different.

Stichwort "Signifikante Stellen"

/Thomas
--
The comp.lang.java.gui FAQ:
http://www.uni-giessen.de/faq/archiv/computer-lang.java.gui.faq/

Thomas Weidenfeller, Jun 7, 2006
10. ### Ingo R. HomannGuest

Hi,

Oliver Wong wrote:
>>>>> BigDecimal bigDecimal = new BigDecimal("1.00");
>>>>> BigDecimal bigDecima2 = new BigDecimal("1");
>>>>>
>>>>> System.out.println(bigDecimal.equals(bigDecima2));

> ...
> As I've mentioned elsewhere in this newsgroup (but not within this
> thread), the concept of equality is context dependent. Are "1.00" and
> "1.0" equal? Perhaps yes, if you're talking about pure mathematical
> numbers. Perhaps no, if you're talking about engineering measurements
> with specific tolerance levels

Ah, OK, that is a point I did not consider! I was only thinking of the
"mathematical" equality.

Still, I am not convinced that the two values should not be mathematical
equal (which you did not say), but I see (and agree to) your point, and
it might be enough to say "they are not *generally* equal".

I know that compareTo() does exactly what I want, but I just think,
"b.compareTo(BigDecimal.ZERO)==0" is not as beautiful and readable as
allowed) "b==BigDecimal.ZERO" (or perhaps "b===BigDecimal.ZERO", if you
think that is is not a good idea to allow to overload the
"referential-equality-comparison-operator" ==).

Ciao,
Ingo, daydreaming ;-)

Ingo R. Homann, Jun 7, 2006
11. ### Ingo R. HomannGuest

Hi,

Patricia Shanahan wrote:
> Anyone who thinks they are equivalent objects, try running this:
>
> import java.math.BigDecimal;
> public class TestBigDecimal {
> public static void main(String[] args) {
> System.out.println(new BigDecimal("1.0").
> divide(new BigDecimal(3),BigDecimal.ROUND_HALF_EVEN));
> System.out.println(new BigDecimal("1.00").
> divide(new BigDecimal(3),BigDecimal.ROUND_HALF_EVEN));
> }
> }
>
> If they really were equivalent, I would expect them to do the same for
> anything other than the identity related operations, == comparison and
> System.identityHashCode().

OK, that's perfectly right. But perhaps, only the specification of the
method divide() is not consistent. Perhaps it would have been better if
you would have been forced to explicitely name the scale of the result:

BigDecimal devide(BigDecimal d, RoundingMode r, scale s) {...}

So, I am not convinced that equals is implemented/specified
mathematically correct.

Or am I missing something?

Ciao,
Ingo

Ingo R. Homann, Jun 8, 2006
12. ### Patricia ShanahanGuest

Ingo R. Homann wrote:
> Hi,
>
> Patricia Shanahan wrote:
>> Anyone who thinks they are equivalent objects, try running this:
>>
>> import java.math.BigDecimal;
>> public class TestBigDecimal {
>> public static void main(String[] args) {
>> System.out.println(new BigDecimal("1.0").
>> divide(new BigDecimal(3),BigDecimal.ROUND_HALF_EVEN));
>> System.out.println(new BigDecimal("1.00").
>> divide(new BigDecimal(3),BigDecimal.ROUND_HALF_EVEN));
>> }
>> }
>>
>> If they really were equivalent, I would expect them to do the same for
>> anything other than the identity related operations, == comparison and
>> System.identityHashCode().

>
> OK, that's perfectly right. But perhaps, only the specification of the
> method divide() is not consistent. Perhaps it would have been better if
> you would have been forced to explicitely name the scale of the result:
>
> BigDecimal devide(BigDecimal d, RoundingMode r, scale s) {...}
>
> So, I am not convinced that equals is implemented/specified
> mathematically correct.
>
> Or am I missing something?

You may be missing something that people have been missing, at times,
for at least 50 years.

The original Fortran type for floating point was called "REAL".
Unfortunately, this encouraged programmers to think of its arithmetic as
real arithmetic, instead of floating point arithmetic. Sometimes, that
got them into trouble because floating point arithmetic differs from
real arithmetic in some critical properties. For example, real addition
is always associative, floating point addition isn't.

You are confusing BigDecimal arithmetic with decimal fraction
arithmetic, and don't like it they turn out to be different, essentially
the same problem as confusing floating point and real arithmetic, and
being disturbed whenever (a+b)+c is different from a+(b+c).

If a BigDecimal were simply a decimal fraction, you would be right about
1.0 == 1.00, and the number would not have a scale attribute, so no
operation results would depend on scale.

A BigDecimal is not just a decimal fraction. BigDecimal is a different,
equally valid, system of arithmetic in which each number has a scale,
and results of arithmetic operations can depend on the scale. The scale
is a guide to the intended precision of the calculation, so it makes
sense to have options to round according to the current scale.

It is not a matter of "mathematically correct" because mathematics, no
matter how much it has to say about decimal fraction arithmetic, says
nothing about java.math.BigDecimal arithmetic. It is a matter of
defining an arithmetic system that is useful for certain purposes.

Of course, to some extent BigDecimal is a model of decimal fraction
arithmetic, but it has its own rules, designed to be useful in a range
of contexts.

Patricia

Patricia Shanahan, Jun 8, 2006
13. ### Chris UppalGuest

Patricia Shanahan wrote:

> It is not a matter of "mathematically correct" because mathematics, no
> matter how much it has to say about decimal fraction arithmetic, says
> nothing about java.math.BigDecimal arithmetic. It is a matter of
> defining an arithmetic system that is useful for certain purposes.
>
> Of course, to some extent BigDecimal is a model of decimal fraction
> arithmetic, but it has its own rules, designed to be useful in a range
> of contexts.

And one could also define an EvenBiggerDecimal class with instances that had no
scale (or, equivalently, whose scale was always unbounded). In that case they
would, up to the limits of available time and memory, correspond exactly to the
mathematical (finite) decimal fractions.

Maybe the problem here is that BigDecimal is misnamed; it would be better
called something like ScaledDecimal.

In a way there's a connection here with numbers used to represent quantities.
One pound does not equal one kilogram, even though they both are represented as
1. In a similar kind of way, 1.00 is not the same as 1.0 since they represent
amounts of different things -- in one case the number of hundredths, in the
other the number of tenths.

-- chris

Chris Uppal, Jun 8, 2006
14. ### Dale KingGuest

Oliver Wong wrote:
>
> [*] An engineer might reject a part that measures "1.0 mm", requiring
> one that measures "1.00 mm". Why? Because that engineer might know that
> if the part actually measures 1.01 mm (which is considered to be a "1.0
> mm" part, but not a "1.00 mm" part), the device will fail and/or break,
> whereas if the device measures 1.004 mm (which is both a "1.0 mm" and
> "1.00 mm" part), the device will tolerate this small deviancy, and
> continue functioning.

I remember in a freshman engineering course the teacher (who came from
industry) told us about a time they were given drawings to make these
large metal disks with these holes in them and the drawing specified the
holes to be 6.000 inches in diameter. They went to a lot of work to get
them to those tolerances. When they got them done they found out that
they were use within a large pipe to slow down the flow. So in reality
they could have been +/- inches.
--
Dale King

Dale King, Jun 11, 2006
15. ### rajends1

Joined:
Aug 7, 2012
Messages:
1
try doublevalue

BigDecimal a = new BigDecimal("0.00");
BigDecimal b = new BigDecimal("0.0");
BigDecimal c = new BigDecimal("0");

if(a.doubleValue()==BigDecimal.ZERO.doubleValue()){
System.out.println("a equals");
}

if(b.doubleValue()==BigDecimal.ZERO.doubleValue()){
System.out.println("b equals");
}

if(c.doubleValue()==BigDecimal.ZERO.doubleValue()){
System.out.println("c equals");
}

rajends1, Aug 7, 2012