I put this into java and I was given the result 2. Was wondering why it isn't an ArithmeticException, as shouldn't (int)(2/0.9) turn into 2/0. All help is appreciated.
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30.9 is a float, so 2 is promoted (or interpreted as) a float, and then the division takes place. The *result* is cast to int. – zzxyz Nov 30 '17 at 00:54
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Oh so the division occurs before the cast? – Matthew Fenel Nov 30 '17 at 00:55
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2@MatthewFenel Of course. `(2/0.9)` is in parentheses no? – Andrew Li Nov 30 '17 at 00:56
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Yes. The parenthesis around `2/0.9` even make that explicit. `2/(int)0.9` should give you the result you are....expecting? – zzxyz Nov 30 '17 at 00:56
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1Oh ok thanks! This is just for computer science lol. – Matthew Fenel Nov 30 '17 at 00:57
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1parenthesis are 'slight' older than computer science, have few hundred years and well understood sense – Jacek Cz Nov 30 '17 at 01:11
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2@zzxyz actually `0.9` is a *double*, not a float. – Bohemian Nov 30 '17 at 02:44
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@Bohemian ah sorry I was using float loosely as in 'floating point' which is probably not a smart thing to do in this situation. – zzxyz Nov 30 '17 at 04:46
1 Answers
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Your code is
(int) (2 / 0.9)
So the int-cast is only applied to the result after computing 2 / 0.9. Now 2 / 0.9 divides an int by a double value. In such a case the int will also be interpreted as double (2.0 in this case). The result is thus like
2.0 / 0.9 = 2.22...
This process is known as numeric promotion (it uses widening primitive conversion here JLS§5.1.2). From JLS§5.6:
A numeric promotion is a process by which, given an arithmetic operator and its argument expressions, the arguments are converted to an inferred target type
T.Tis chosen during promotion such that each argument expression can be converted toTand the arithmetic operation is defined for values of typeT.
After that you cast to int which will round the value to the next lower integer, 2 in this case. Thus the result is 2.
What you expected would be the result of an expression like
2 / (int) 0.9
// or more explicit:
2 / ((int) 0.9)
which first casts the 0.9 to an int before dividing. In this case you would correctly get
2 / 0
yielding the expected ArithmeticException.
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