internal int to double cast

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Bart Rider - 10 May 2006 12:59 GMT

Hi there,

I just want to have a confirmation. I have two
variables like this:
    int i = 10;
    double d = 10.1;

Now I test whether d is greater and do such a thing:
    if (i<d)
        greater_double();
    else
        smaller_or_equal_double();

My question is the following. Does Java internally
converts the int(eger) i to double before comparison
(as I assume it does) or might there be circumstances
where it did not in such a case?

Best regards,
Bart

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Hendrik Maryns - 10 May 2006 13:27 GMT

Bart Rider schreef:

> Hi there,
>
[quoted text clipped - 13 lines]
> (as I assume it does) or might there be circumstances
> where it did not in such a case?

It does. See
http://java.sun.com/docs/books/jls/second_edition/html/conversions.doc.html#26917

HTH, H.

- --
Hendrik Maryns

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liuyanbupt@gmail.com - 10 May 2006 13:34 GMT

I find the following statements in "The Java Language Specification
Third Edition":
-----------------------------------------------------------------------------------------------------------------
5.6.2 Binary Numeric Promotion
...
· If either operand is of type double, the other is converted to
double.
...

15.20.1 Numerical Comparison Operators <, <=, >, and >=
The type of each of the operands of a numerical comparison operator
must be a
type that is convertible (§5.1.8) to a primitive numeric type, or a
compile-time
error occurs. Binary numeric promotion is performed on the operands
(§5.6.2). If
the promoted type of the operands is int or long, then signed integer
comparison
is performed; if this promoted type is float or double, then
floating-point comparison
is performed.
-----------------------------------------------------------------------------------------------------------------
So, I think what you assumed is the right answer.

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Thomas Fritsch - 10 May 2006 13:40 GMT

Bart Rider schrieb:

> I just want to have a confirmation. I have two
> variables like this:
[quoted text clipped - 11 lines]
> (as I assume it does) or might there be circumstances
> where it did not in such a case?

Just one addition to what the other posters correctly said:

You can check it by disassembling your java class with "javap -c ...".
There should be an "i2d" (int to double) instruction.

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"Thomas:Fritsch$ops:de".replace(':','.').replace('$','@')

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Patricia Shanahan - 10 May 2006 14:01 GMT

> Hi there,
>
[quoted text clipped - 16 lines]
> Best regards,
> Bart

The JLS requires the same answer as if the program did the conversion of
i to double followed by the comparison.

An optimizing compiler might not actually generate the conversion, if it
noticed that i<d is a constant expression, did the comparison at compile
time, found that is is always true, and collapsed the if statement.

Patricia

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internal int to double cast

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