How to test if a double is an integer

Question

Is it possible to do this   double variable  variable   5     the below should return true  since 5 is an int   if variable were to equal 5 7  then it would return false     if variable    int          do stuff     I know the code probably doesn t go anything like that  but how does it go

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public static boolean isInt double d        return d     int  d

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if   variable    Math floor variable    amp  amp   Double isInfinite variable            integer type     This checks if the rounded-down value of the double is the same as the double   Your variable could have an int or double value and Math floor variable  always has an int value  so if your variable is equal to Math floor variable  then it must have an int value   This also doesn t work if the value of the variable is infinite or negative infinite hence adding  as long as the variable isn t inifinite  to the condition

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Here is a good solution   if  variable     int variable          logic

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The best way is with modulus operator  if val   1    0

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Similar to SkonJeet s answer above  but the performance is better  at least in java    Double zero   0d      zero longValue      zero doubleValue

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My simple solution  private boolean checkIfInt double value    return value - Math floor value     0

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Guava  DoubleMath isMathematicalInteger    Disclosure  I wrote it    Or  if you aren t already importing Guava  x    Math rint x  is the fastest way to do it  rint is measurably faster than floor or ceil

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A simple way for doing this could be     double d   7 88       sample example     int x floor d         floor of number     int y ceil d          ceil of number     if x  y               both floor and ceil will be same for integer number         cout lt  lt  quot integer number quot       else         cout lt  lt  quot double number quot

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Try this way   public static boolean isInteger double number       return Math ceil number     Math floor number        for example     Math ceil 12 9    13  Math floor 12 9    12    hence 12 9 is not integer   nevertheless    Math ceil 12 0    12  Math floor 12 0   12     hence 12 0 is integer

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Personally  I prefer the simple modulo operation solution in the accepted answer  Unfortunately  SonarQube doesn t like equality tests with floating points without setting a round precision  So we have tried to find a more compliant solution  Here it is   if  new BigDecimal decimalValue  remainder new BigDecimal 1   equals BigDecimal ZERO            no decimal places   else          decimal places     Remainder BigDecimal  returns a BigDecimal whose value is  this   divisor   If this one s equal to zero  we know there is no floating point

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Here s a solution   float var   Your Value  if   var - Math floor var      0 0f           var is an integer  so do stuff

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Because of   operator cannot apply to BigDecimal and int  i e  1  directly  so I am using the following snippet to check if the BigDecimal is an integer  value stripTrailingZeros   scale    lt   0

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Consider   Double isFinite  value   amp  amp  Double compare  value  StrictMath rint  value      0   This sticks to core Java and avoids an equality comparison between floating point values      which is consdered bad   The isFinite   is necessary as rint   will pass-through infinity values

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Or you could use the modulo operator    d   1     0

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public static boolean isInteger double d         Note that Double NaN is not equal to anything  even itself    return  d    Math floor d    amp  amp   Double isInfinite d

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you could try in this way  get the integer value of the double  subtract this from the original double value  define a rounding range and tests if the absolute number of the new double value without the integer part  is larger or smaller than your defined range  if it is smaller you can intend it it is an integer value  Example   public final double testRange   0 2   public static boolean doubleIsInteger double d       int i    int d      double abs   Math abs d-i       return abs  lt   testRange      If you assign to d the value 33 15 the method return true  To have better results you can assign lower values to testRange  as 0 0002  at your discretion

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Here s a version for Integer and Double       private static boolean isInteger Double variable        if      variable equals Math floor variable    amp  amp                Double isInfinite variable            amp  amp               Double isNaN variable                 amp  amp              variable  lt   Integer MAX VALUE          amp  amp              variable  gt   Integer MIN VALUE            return true        else           return false            To convert Double to Integer   Integer intVariable   variable intValue

[java] How to test if a double is an integer

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