TheAlgorithms/Java · error · NumberFormatException

Input parameter must not be empty!

Error message

Input parameter must not be empty!

What it means

Thrown by ParseInteger.checkInput when the input string s is empty (s.isEmpty()). An empty string has no digits and cannot represent an integer, so parsing would be meaningless. This is the second guard, after the null check.

Solutions

1. Validate that the trimmed string is non-empty before parsing: if (s == null || s.isBlank()) handle accordingly.
2. Treat empty input as a domain-level missing value rather than passing it through to parse.
3. Sanitize upstream: filter out empty tokens from splits before iteration.

Example fix

// before
int v = ParseInteger.parse(raw);

// after
if (raw == null || raw.isBlank()) {
    throw new IllegalArgumentException("raw is missing");
}
int v = ParseInteger.parse(raw.trim());

if (s == null || s.isBlank()) {
    throw new IllegalArgumentException("input is missing");
}
int v = ParseInteger.parse(s.trim());

try {
    int v = ParseInteger.parse(s);
} catch (NumberFormatException e) {
    throw new IllegalArgumentException("invalid integer input: " + s, e);
}

When it happens

Trigger: Calling the public parse method with "" — e.g., ParseInteger.parse("").

Common situations: User submitted an empty form field; a CSV/regex split produced an empty token; a default value of "" was never overwritten; trimming whitespace left an empty string.

Related errors

• Input parameter must not be null!
• Input parameter of incorrect format:
• Input string must be a valid integer
• additivePersistence() does not accept negative values
• All side lengths must be positive

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/2b80aea5c56cd4db. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/com/thealgorithms/maths/ParseInteger.java:12

package com.thealgorithms.maths;

public final class ParseInteger {
    private ParseInteger() {
    }

    private static void checkInput(final String s) {
        if (s == null) {
            throw new NumberFormatException("Input parameter must not be null!");
        }
        if (s.isEmpty()) {
            throw new NumberFormatException("Input parameter must not be empty!");
        }
    }

    private static void checkDigitAt(final String s, final int pos) {
        if (!Character.isDigit(s.charAt(pos))) {
            throw new NumberFormatException("Input parameter of incorrect format: " + s);
        }
    }

    private static int digitToInt(final char digit) {
        return digit - '0';
    }

    /**
     * Parse a string to integer
     *
     * @param s the string
     * @return the integer value represented by the argument in decimal.

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