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    <p>For the same reason that there is no integer <code>NaN</code> in any other language.</p> <p>Modern computers use 2's complement binary representation for integers, and that representation doesn't have a NaN value. (All values in the domain of the representation type represent definite integers.) </p> <p>It follows that computer integer arithmetic hardware does not recognize any NaN representation. </p> <p>In theory, someone could invent an alternative representation for integers that includes NaN (or INF, or some other exotic value). However, arithmetic using such a representation would not be supported by the hardware. While it would be possible to implement it in software, it would be prohibitively expensive<sup>1</sup>... and undesirable in other respects too to include this support in the Java language.</p> <p><sup>1 - It is of course relative, but I'd anticipate that a software implementation of NaNs would be (at least) an order of magnitude slower than hardware. If you actually, really, needed this, then that would be acceptable. But the vast majority of integer arithmetic codes don't need this. In most cases throwing an exception for "divide by zero" is just fine, and an order of magnitude slow down in all integer arithmetic operations is ... not acceptable.</sup></p> <hr> <p>By contrast:</p> <ul> <li>the "unused" values in the representation space already exist</li> <li>NaN and INF values are part of the IEE floating point standard, and</li> <li>they are (typically) implemented by the native hardware implementation of floating point arithmetic</li> </ul>
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    1. POWhy doesn't Integer represent NaN in Java?
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    1. COI disagree about "prohibitively expensive" - that's a relative term, it may be cheaper than the cost of coding around the issue. And undesirable - dunno, maybe. I would say that if the concept exists for double, it could be usaful for ints. It's only because the underlying implementation of int doesn't provide for it that it isn't done, which practically implies that since double's internal representation and range *does* allow for it that it's a good idea that needs a different implementation to exist.
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    2. CO@Bohemian - we are talking about it being prohibitively expensive to make NaN integers part of "the language". Obviously, if an application really needs NaNs, it it is not prohibitively expensive for them. But most don't.
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    3. COYes, I know what you meant. But that "expense" (apart from the effort to change the language, which doesn't affect us programmers) would ultimately translate into higher CPU usage when dealing with ints, and it is *that* cost (which may be converted to dollars) that I am comparing the "cost" of the extra functionality gained (again convertable to dollars). Whether it is "prohibitive" or not depends on those dollar cost. I actually doubt very much whether it would be "prohibitive" - we are talking about changing, or rather adding to, the underlying implementation, which should be left "hidden",
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