java how to check that a number is an integer?

To check if a number is an integer in Java, you can use the 'isInteger' method of the 'NumberUtils' class of the Apache Commons Lang library. This method takes a string as an argument and returns 'true' if the string represents an integer, or 'false' otherwise.

Here's an example of how to use the 'isInteger' method to check if a number is an integer:

import org.apache.commons.lang3.math.NumberUtils;

public class Main {
  public static void main(String[] args) {
    String str = "123";

    if (NumberUtils.isInteger(str)) {
      System.out.println("The string is an integer");
    } else {
      System.out.println("The string is not an integer");
    }
  }
}

This example uses the 'isInteger' method to check whether the string '"123"' represents an integer. Because the string is an integer, the method returns 'true' and the message "The string is an integer" is printed.

Note that the 'isInteger' method can only check whether a string represents an integer. If you want to verify whether a number is an integer using another type of data, such as a numeric variable, you must use another approach. For example, you can use the module operator ('%') to check if a number is divisible by 1 without leaving any remainder:

int num = 123;

if (num % 1 == 0) {
  System.out.println("The number is integer");
} else {
  System.out.println("The number is not an integer");
}