Question

How to check whether a floating-point variable is an integer (has no fractional part) in Java

Answer 1

class Program {
    public static void main(String[] args) {
        double d = 24278.0;
        
        if (d == Math.floor(d)) {
            System.out.println("The double variable contains an integer");
        } else {
            System.out.println("The double variable contains a floating point");
        }
    }
}




/*
run:
 
The double variable contains an integer
 
*/

 

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Answer 2

public class DoubleIntegerLikeCheck {

    // -------------------------------------------------------------------------
    // Determines whether a double represents an integer value.
    // Uses a small tolerance to handle floating‑point precision issues.
    // -------------------------------------------------------------------------
    public static boolean isInteger(double value) {
        final double epsilon = 1e-12;

        // Casting to long truncates toward zero; compare with tolerance.
        long truncated = (long) value;

        // If the absolute difference is extremely small, treat it as an integer.
        return Math.abs(value - truncated) < epsilon;
    }

    // -------------------------------------------------------------------------
    // Prints a descriptive message for the given double.
    // -------------------------------------------------------------------------
    public static void printCheck(double value) {
        System.out.println("Checking value: " + value);

        if (isInteger(value)) {
            System.out.println("Result: The value contains an integer.\n");
        } else {
            System.out.println("Result: The value contains a floating-point number.\n");
        }
    }

    // -------------------------------------------------------------------------
    // Entry point.
    // -------------------------------------------------------------------------
    public static void main(String[] args) {

        // Example input values
        double a = 42.0;                 // integer-like
        double b = 42.00000000001;       // floating-point due to tiny fraction
        double c = 89.0000000000001;     // integer-like
        double d = -7.0;                 // negative integer-like
        double e = 3.14;                 // floating-point

        // Run checks
        printCheck(a);
        printCheck(b);
        printCheck(c);
        printCheck(d);
        printCheck(e);
    }
}


/*
run:

Checking value: 42.0
Result: The value contains an integer.

Checking value: 42.00000000001
Result: The value contains a floating-point number.

Checking value: 89.0000000000001
Result: The value contains an integer.

Checking value: -7.0
Result: The value contains an integer.

Checking value: 3.14
Result: The value contains a floating-point number.

*/

 

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