TheAlgorithms/Java · warning · IllegalArgumentException

Cannot convert NaN to long!

Error message

Cannot convert NaN to long!

What it means

Thrown inside MathBuilder.toLong() when the internal result is NaN. IMPORTANT: this exception is immediately caught by the method's own catch (Exception ex) block at line 44, which silently returns 0. The caller never sees the exception; the observable symptom is that toLong() returns an unexpected 0. NaN typically results from operations like sqrt of a negative number, log of a negative, or 0.0/0.0.

Source

Thrown at src/main/java/com/thealgorithms/maths/MathBuilder.java:29

 * Date: Oct 20, 2024
 */
public final class MathBuilder {
    private final double result;

    private MathBuilder(Builder builder) {
        this.result = builder.number;
    }

    // Returns final result
    public double get() {
        return result;
    }

    // Return result in long
    public long toLong() {
        try {
            if (Double.isNaN(result)) {
                throw new IllegalArgumentException("Cannot convert NaN to long!");
            }
            if (result == Double.POSITIVE_INFINITY) {
                return Long.MAX_VALUE;
            }
            if (result == Double.NEGATIVE_INFINITY) {
                return Long.MIN_VALUE;
            }
            if (result > Long.MAX_VALUE) {
                return Long.MAX_VALUE;
            }
            if (result < Long.MIN_VALUE) {
                return Long.MIN_VALUE;
            }
            return Math.round(result);
        } catch (Exception ex) {
            return 0;
        }
    }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Check Double.isNaN(builder.get()) before calling toLong() to detect NaN results
2. Avoid operations that produce NaN: validate inputs to sqrt, log, and division before applying them
3. Be aware that toLong() silently returns 0 for NaN — do not rely on it to signal errors

Example fix

// before
MathBuilder mb = new MathBuilder.Builder(-1.0).sqrt().build();
long result = mb.toLong();  // silently returns 0

// after
MathBuilder mb = new MathBuilder.Builder(-1.0).sqrt().build();
if (Double.isNaN(mb.get())) {
    throw new ArithmeticException("Result is NaN, cannot convert to long");
}
long result = mb.toLong();

MathBuilder mb = builder.build();
double value = mb.get();
if (Double.isNaN(value)) {
    throw new ArithmeticException("MathBuilder result is NaN, cannot convert to long");
}
long result = mb.toLong();

static boolean isConvertibleToLong(double value) {
    return !Double.isNaN(value);
}

When it happens

Trigger: Building a MathBuilder whose result is NaN (e.g., via sqrt() on a negative, log() on a negative) and then calling toLong(). The caller gets 0, not the exception. The exception is only visible in a debugger or if the catch block is removed.

Common situations: Chaining builder operations that produce NaN without checking intermediate state. Debugging why toLong() returns 0 unexpectedly — the swallowed exception hides the real cause.

Related errors

• Number must be zero for random assignment!
• Number must be zero for PI assignment!
• Number must be zero for E assignment!
• Number must be zero to set!
• Slope and intercept must be valid numbers.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/505d402ca5eafa02. Report an issue: GitHub.