Java percent of number

Question

Is there any way to calculate (for example) 50% of 120? I tried:

int k = (int)(120 / 100)*50;

But it doesn't work.

You're integer dividing 120 by 100, which is 1. You'll need to multiply by 50 first, then divide, or use floats. — Joachim Isaksson, Aug 03 '13 at 16:20

score 45 · Accepted Answer · answered Aug 03 '13 at 16:30

45

int k = (int)(120 / 100)*50;

The above does not work because you are performing an integer division expression (120 / 100) which result is integer 1, and then multiplying that result to 50, giving the final result of 50.

If you want to calculate 50% of 120, use:

int k = (int)(120*(50.0f/100.0f));

more generally:

int k = (int)(value*(percentage/100.0f));

answered Aug 03 '13 at 16:30

Lake

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Or, you know, `120/2`. – Qix - MONICA WAS MISTREATED Mar 05 '16 at 23:02

Eric Urban · Answer 2 · 2013-08-03T16:29:22.263

5

int k = (int)(120*50.0/100.0);

edited Aug 03 '13 at 16:29

answered Aug 03 '13 at 16:17

Eric Urban

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why complicate? inner parenthesis is not actually required. – Ankit Aug 03 '13 at 16:27

score 4 · Answer 3 · answered Aug 03 '13 at 16:30

Never use floating point primitive types if you want exact numbers and consistent results, instead use BigDecimal.

The problem with your code is that result of (120/100) is 1, since 120/100=1.2 in reality, but as per java, int/int is always an int. To solve your question for now, cast either value to a float or double and cast result back to int.

score 2 · Answer 4 · answered Aug 03 '13 at 16:23

I suggest using BigDecimal, rather than float or double. Division by 100 is always exact in BigDecimal, but can cause rounding error in float or double.

That means that, for example, using BigDecimal 50% of x plus 30% of x plus 20% of x will always sum to exactly x.

score 1 · Answer 5 · edited Mar 05 '16 at 22:55

1

it is simple as 2 * 2 = 4 :)

int k = (int)(50 * 120) / 100;

edited Mar 05 '16 at 22:55

Tunaki

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answered Mar 05 '16 at 22:47

Konstantin F

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score -1 · Answer 6 · answered Aug 03 '13 at 16:37

-1

Division must be float, not int

(120f * 50 / 100f)

answered Aug 03 '13 at 16:37

Lore Lai

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score -1 · Answer 7 · answered Aug 03 '13 at 17:33

-1

You don't need floating point in this case you can write

int i = 120 * 50 / 100;

or

int i = 120 / 2;

answered Aug 03 '13 at 17:33

Peter Lawrey

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Java percent of number

7 Answers7