java : multiplying 2 doubles

Question

double multiply() 
{
 double x=(2/3)*3.14*1.02;
 System.out.print(x);

 double y=0.666*3.14*1.02; /*(2/3)=0.666...*/
 System.out.print(y);
}

Output: x=0.0 y=SomeNumber

please explain this?

Aren't you familiar with the joke? You have 6 programmers and 5 slices of cake. How much cake does each programmer get? 0, of course. — Neil, Feb 19 '16 at 14:13

Tilman Hausherr · Accepted Answer · 2016-02-19T14:19:15.577

2

(2/3) is 0.

because both are integers. To solve this, use a cast or make it clear that your number is not an integer:

double x=(2/3d)*3.14*1.02;

Now you have an integer divided by a double, which results in a double.

Some more to read about this: http://www.mathcs.emory.edu/~cheung/Courses/170/Syllabus/04/mixed.html

edited Feb 19 '16 at 14:19

answered Feb 19 '16 at 14:12

Tilman Hausherr

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Not a good idea to write 3f in this case since 2/3f will be evaluated as a `float` which will cost you precision as the promotion to `double` happens subsequently. – Bathsheba Feb 19 '16 at 14:16
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*Much* nicer. Have an upvote. – Bathsheba Feb 19 '16 at 14:19

Bathsheba · Answer 2 · 2016-02-19T15:36:07.030

1

(2/3) is computed first (because of the parentheses), and in integer arithmetic (since the number literals are of type int). The fractional part is discarded.

It is therefore an int type with a value of 0. The entire expression is therefore zero.

The obvious remedy is to remove the parentheses and write 2.0 / 3.0 instead. Some folk prefer an explicit cast, but I find that ugly.

edited Feb 19 '16 at 15:36

answered Feb 19 '16 at 14:13

Bathsheba

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score 0 · Answer 3 · answered Feb 19 '16 at 14:09

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2/3 = 0 because they don't have explicit cast to double they are integers. The whole expression becomes: double x=0*3.14*1.02; which is 0.

answered Feb 19 '16 at 14:09

Alexandru Cimpanu

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score 0 · Answer 4 · answered Feb 19 '16 at 14:10

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because data type of both 2 and 3 is int and int/int gives you int which in your case 2/3 is 0. Try using 2.0/3 or 2/3.0 you will get the required answer.

answered Feb 19 '16 at 14:10

Shashank Sharma

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score 0 · Answer 5 · answered Feb 19 '16 at 14:10

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Suffix every number with a 'd' to be sure you are dealing with doubles

answered Feb 19 '16 at 14:10

Benjamin

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java : multiplying 2 doubles

5 Answers5