How to trim double value

[vanlalhmangaiha khiangte]

 
String[] Numbers={"8.20","4.69","7.87","8.93","2.61","0.22","8.28"};
double constant=2.0;
double numb;
for(int i=0;i<Numbers.length;i++)
{
numb=Double.parseDouble(Numbers[i]);
System.out.println("Number "+i+" Value="+(numb+constant));
}
 
Output:-
Number 0 Value=10.2
Number 1 Value=6.69
Number 2 Value=9.870000000000001
Number 3 Value=10.93
Number 4 Value=4.609999999999999
Number 5 Value=2.22
Number 6 Value=10.28
  

How do i trim the double values upto two decimal places?
9.870000000000001 should be 9.87
4.609999999999999 should be 4.61
Why this values are different ?

Thanks in advance

[Campbell Ritchie]

This is normal behaviour for floating-point aruthmetic. It is like calculating 1/3 = 0.333333333333333333 in decimal, then 1/3 * 3 = 0.999999999999999999 and when you subtract it from 1 you get 0.00000000000000000001. (Or something like that.) There are some numbers which cannot round like that at all, which is why you are getting numbers ending with 0000000001 or 9999999999.
That is why you shouldn't use floating point arithmetic for money or as the counter for a for loop.

Suggest what you actually want is to print out the numbers with a particular precision, rather than rounding.

Try the % tags which are described in the API for the Formatter class. There is more about the % tags in the Java Tutorial here. You probably want something like
System.out.printf("Number = %6.2f%n", doubleNumber);

[Ulf Dittmer]

Links to more in-depth explanations about floating point acccuracy can be found under #20 in the http://faq.javaranch.com/java/JavaBeginnersFaq