Checking if a number is an Integer in Java

Is there any method or quick way to check whether a number is an Integer (belongs to Z field) in Java?

I thought of maybe subtracting it from the rounded number, but I didn't find any method that will help me with this.

Where should I check? Integer Api?

Quick and dirty...

if (x == (int)x)
{
   ...
}

edit: This is assuming x is already in some other numeric form. If you're dealing with strings, look into Integer.parseInt.

One example more :)

double a = 1.00

if(floor(a) == a) {
   // a is an integer
} else {
   //a is not an integer.
}

In this example, ceil can be used and have the exact same effect.

if you're talking floating point values, you have to be very careful due to the nature of the format.

the best way that i know of doing this is deciding on some epsilon value, say, 0.000001f, and then doing something like this:

boolean nearZero(float f)
{
    return ((-episilon < f) && (f <epsilon)); 
}

then

if(nearZero(z-(int)z))
{ 
    //do stuff
}

essentially you're checking to see if z and the integer case of z have the same magnitude within some tolerance. This is necessary because floating are inherently imprecise.

NOTE, HOWEVER: this will probably break if your floats have magnitude greater than Integer.MAX_VALUE (2147483647), and you should be aware that it is by necessity impossible to check for integral-ness on floats above that value.

With Z I assume you mean Integers , i.e 3,-5,77 not 3.14, 4.02 etc.

A regular expression may help:

Pattern isInteger = Pattern.compile("\\d+");

    if((number%1)!=0)
    {
        System.out.println("not a integer");
    }
    else
    {
        System.out.println("integer");
    }

 int x = 3;

 if(ceil(x) == x) {

  System.out.println("x is an integer");

 } else {

  System.out.println("x is not an integer");

 }

user3080471

change x to 1 and output is integer, else its not an integer add to count example whole numbers, decimal numbers etc.

   double x = 1.1;
   int count = 0;
   if (x == (int)x)
    {
       System.out.println("X is an integer: " + x);
       count++; 
       System.out.println("This has been added to the count " + count);
    }else
   {
       System.out.println("X is not an integer: " + x);
       System.out.println("This has not been added to the count " + count);


   }

/**
 * Check if the passed argument is an integer value.
 *
 * @param number double
 * @return true if the passed argument is an integer value.
 */
boolean isInteger(double number) {
    return number % 1 == 0;// if the modulus(remainder of the division) of the argument(number) with 1 is 0 then return true otherwise false.
}

Check if ceil function and floor function returns the same value

static boolean isInteger(int n) 
{ 
return (int)(Math.ceil(n)) == (int)(Math.floor(n)); 
}

Klevie Jun

// in C language.. but the algo is same

#include <stdio.h>

int main(){
  float x = 77.6;

  if(x-(int) x>0)
    printf("True! it is float.");
  else
    printf("False! not float.");        

  return 0;
}

来源：https://stackoverflow.com/questions/5502548/checking-if-a-number-is-an-integer-in-java

标签

java

utilities