In Java what does NaN mean

Question

I have a program that tries to shrink a double down to a desired number  The output I get is NaN   What does NaN mean in Java

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Not a Java guy  but in JS and other languages I use it s  Not a Number   meaning some operation caused it to become not a valid number

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NaN means  Not a Number  and is the result of undefined operations on floating point numbers like for example dividing zero by zero   Note that while dividing a non-zero number by zero is also usually undefined in mathematics  it does not result in NaN but in positive or negative infinity

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NaN means  Not a number   It s a special floating point value that means that the result of an operation was not defined or not representable as a real number   See here for more explanation of this value

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NaN   Not a Number

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It literally means  Not a Number   I suspect something is wrong with your conversion process   Check out the Not A Number section at this reference

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Means Not a Number  It is a common representation for an impossible numeric value in many programming languages

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Taken from this page       NaN  stands for  not a number    Nan    is produced if a floating point   operation has some input parameters   that cause the operation to produce   some undefined result  For example    0 0 divided by 0 0 is arithmetically undefined  Taking the square root of a   negative number is also undefined

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NaN stands for Not a Number  It is used to signify any value that is mathematically undefined  Like dividing 0 0 by 0 0  You can look here for more information  https   web archive org web 20120819091816 http   www concentric net  ttwang tech javafloat htm  Post your program here if you need more help

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NaN means    Not a Number    and is basically a representation of a special floating point value in the IEE 754 floating point standard  NaN generally means that the value is something that cannot be expressed with a valid floating point number   A conversion will result in this value  when the value being converted is something else  for example when converting a string that does not represent a number

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Not a valid floating-point value  e g  the result of division by zero   http   en wikipedia org wiki NaN

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Minimal runnable example  The first thing that you have to know  is that the concept of NaN is implemented directly on the CPU hardware   All major modern CPUs seem to follow IEEE 754 which specifies floating point formats  and NaNs  which are just special float values  are part of that standard   Therefore  the concept will be the very similar across any language  including Java which just emits floating point code directly to the CPU   Before proceeding  you might want to first read up the following answers I ve written    a quick refresher of the IEEE 754 floating point format  What is a subnormal floating point number  some lower level NaN basics covered using C   C    What is difference between quiet NaN and signaling NaN    Now for some Java action  Most of the functions of interest that are not in the core language live inside java lang Float   Nan java  import java lang Float  import java lang Math   public class Nan       public static void main String   args               Generate some NaNs          float nan              Float NaN          float zero div zero    0 0f   0 0f          float sqrt negative     float Math sqrt -1 0           float log negative      float Math log -1 0           float inf minus inf    Float POSITIVE INFINITY - Float POSITIVE INFINITY          float inf times zero   Float POSITIVE INFINITY   0 0f          float quiet nan1       Float intBitsToFloat 0x7fc00001           float quiet nan2       Float intBitsToFloat 0x7fc00002           float signaling nan1   Float intBitsToFloat 0x7fa00001           float signaling nan2   Float intBitsToFloat 0x7fa00002           float nan minus        -nan              Generate some infinities          float positive inf     Float POSITIVE INFINITY          float negative inf     Float NEGATIVE INFINITY          float one div zero     1 0f   0 0f          float log zero          float Math log 0 0               Double check that they are actually NaNs          assert  Float isNaN nan           assert  Float isNaN zero div zero           assert  Float isNaN sqrt negative           assert  Float isNaN inf minus inf           assert  Float isNaN inf times zero           assert  Float isNaN quiet nan1           assert  Float isNaN quiet nan2           assert  Float isNaN signaling nan1           assert  Float isNaN signaling nan2           assert  Float isNaN nan minus           assert  Float isNaN log negative               Double check that they are infinities          assert  Float isInfinite positive inf           assert  Float isInfinite negative inf           assert  Float isNaN positive inf           assert  Float isNaN negative inf           assert one div zero    positive inf          assert log zero    negative inf                 Double check infinities              See what they look like          System out printf  nan            0x 08x  f n   Float floatToRawIntBits nan              nan                      System out printf  zero div zero  0x 08x  f n   Float floatToRawIntBits zero div zero    zero div zero            System out printf  sqrt negative  0x 08x  f n   Float floatToRawIntBits sqrt negative    sqrt negative            System out printf  log negative   0x 08x  f n   Float floatToRawIntBits log negative     log negative             System out printf  inf minus inf  0x 08x  f n   Float floatToRawIntBits inf minus inf    inf minus inf            System out printf  inf times zero 0x 08x  f n   Float floatToRawIntBits inf times zero   inf times zero           System out printf  quiet nan1     0x 08x  f n   Float floatToRawIntBits quiet nan1       quiet nan1               System out printf  quiet nan2     0x 08x  f n   Float floatToRawIntBits quiet nan2       quiet nan2               System out printf  signaling nan1 0x 08x  f n   Float floatToRawIntBits signaling nan1   signaling nan1           System out printf  signaling nan2 0x 08x  f n   Float floatToRawIntBits signaling nan2   signaling nan2           System out printf  nan minus      0x 08x  f n   Float floatToRawIntBits nan minus        nan minus                System out printf  positive inf   0x 08x  f n   Float floatToRawIntBits positive inf     positive inf             System out printf  negative inf   0x 08x  f n   Float floatToRawIntBits negative inf     negative inf             System out printf  one div zero   0x 08x  f n   Float floatToRawIntBits one div zero     one div zero             System out printf  log zero       0x 08x  f n   Float floatToRawIntBits log zero         log zero                     NaN comparisons always fail             Therefore  all tests that we will do afterwards will be just isNaN          assert   1 0f  lt  nan           assert   1 0f    nan           assert   1 0f  gt  nan           assert   nan    nan               NaN propagate through most operations          assert Float isNaN nan   1 0f           assert Float isNaN 1 0f   nan           assert Float isNaN nan   nan           assert Float isNaN nan   1 0f           assert Float isNaN 1 0f   nan           assert Float isNaN  float Math sqrt  double nan              GitHub upstream   Run with   javac Nan java  amp  amp  java -ea Nan   Output   nan            0x7fc00000 NaN zero div zero  0x7fc00000 NaN sqrt negative  0xffc00000 NaN log negative   0xffc00000 NaN inf minus inf  0x7fc00000 NaN inf times zero 0x7fc00000 NaN quiet nan1     0x7fc00001 NaN quiet nan2     0x7fc00002 NaN signaling nan1 0x7fa00001 NaN signaling nan2 0x7fa00002 NaN nan minus      0xffc00000 NaN positive inf   0x7f800000 Infinity negative inf   0xff800000 -Infinity one div zero   0x7f800000 Infinity log zero       0xff800000 -Infinity   So from this we learn a few things    weird floating operations that don t have any sensible result give NaN    0 0f   0 0f sqrt -1 0f  log -1 0f    generate a NaN   In C  it is actually possible to request signals to be raised on such operations with feenableexcept to detect them  but I don t think it is exposed in Java  Why does integer division by zero 1 0 give error but floating point 1 0 0 returns  quot Inf quot   weird operations that are on the limit of either plus or minus infinity however do give  - infinity instead of NaN   1 0f   0 0f log 0 0f    0 0 almost falls in this category  but likely the problem is that it could either go to plus or minus infinity  so it was left as NaN  if NaN is the input of a floating operation  the output also tends to be NaN there are several possible values for NaN 0x7fc00000  0x7fc00001  0x7fc00002  although x86 64 seems to generate only 0x7fc00000  NaN and infinity have similar binary representation   Let s break down a few of them   nan            0x7fc00000   0 11111111 10000000000000000000000 positive inf   0x7f800000   0 11111111 00000000000000000000000 negative inf   0xff800000   1 11111111 00000000000000000000000                                                                                 mantissa                               exponent                                                           sign   From this we confirm what IEEE754 specifies    both NaN and infinities have exponent    255  all ones  infinities have mantissa    0  There are therefore only two possible infinities    and -  differentiated by the sign bit NaN has mantissa    0  There are therefore several possibilities  except for mantissa    0 which is infinity  NaNs can be either positive or negative  top bit   although it this has no effect on normal operations   Tested in Ubuntu 18 10 amd64  OpenJDK 1 8 0 191

[java] In Java, what does NaN mean?

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