TheAlgorithms/Java · error · IllegalArgumentException

Input must be a non-empty binary string.

Error message

Input must be a non-empty binary string.

What it means

Thrown by OnesComplement.onesComplement(String) when the input is null or empty. The method inverts each bit of a binary string; with no characters there is nothing to invert, so null and empty strings are rejected before processing begins.

Source

Thrown at src/main/java/com/thealgorithms/bitmanipulation/OnesComplement.java:24

 *            The class OnesComplement computes the complement of binary number
 *            and returns
 *            the complemented binary string.
 * @return the complimented binary string
 */
public final class OnesComplement {
    private OnesComplement() {
    }

    /**
     * Returns the 1's complement of a binary string.
     *
     * @param binary A string representing a binary number (e.g., "1010").
     * @return A string representing the 1's complement.
     * @throws IllegalArgumentException if the input is null or contains characters other than '0' or '1'.
     */
    public static String onesComplement(String binary) {
        if (binary == null || binary.isEmpty()) {
            throw new IllegalArgumentException("Input must be a non-empty binary string.");
        }

        StringBuilder complement = new StringBuilder(binary.length());
        for (char bit : binary.toCharArray()) {
            switch (bit) {
                case '0' -> complement.append('1');
                case '1' -> complement.append('0');
                default -> throw new IllegalArgumentException("Input must contain only '0' and '1'. Found: " + bit);
            }
        }
        return complement.toString();
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Validate the string is non-null and non-empty before calling.
2. Treat empty input as a no-op/empty result upstream rather than passing it through.
3. Provide a default non-empty binary string when the source is missing.

Example fix

// before
String out = OnesComplement.onesComplement(inputField.getText());

// after
String raw = inputField.getText();
String out = (raw == null || raw.isEmpty()) ? "" : OnesComplement.onesComplement(raw);

if (binary == null || binary.isEmpty()) {
    return ""; // or throw your own error
}
String out = OnesComplement.onesComplement(binary);

static boolean isNonEmptyBinary(String s) { return s != null && !s.isEmpty(); }

try {
    String out = OnesComplement.onesComplement(binary);
} catch (IllegalArgumentException e) {
    out = ""; // nothing to invert
}

When it happens

Trigger: Calling onesComplement(null) or onesComplement(""). Also triggered by a value that becomes empty after trim(), or a field/config that was never set.

Common situations: User input left blank; reading from a property file where the key is absent (null); trimming whitespace-padded input down to empty.

Related errors

• Input must contain only '0' and '1'. Found: {}
• Input must contain only '0' and '1'.
• Input cannot be negative
• The exponent must be positive
• Input data contains invalid characters. Only uppercase A-Z a

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/01b32d2ebb411ee5. Report an issue: GitHub.