TheAlgorithms/Java · error · IllegalArgumentException

The input matrix cannot be empty

Error message

The input matrix cannot be empty

What it means

Thrown by MatrixUtil.validateInputMatrix when matrix.length == 0 — the outer array exists but contains zero rows. Matrix operations need at least one row to determine column count and perform arithmetic; an empty matrix (0x0) is degenerate. This check follows the null check and precedes the row-validity check.

Source

Thrown at src/main/java/com/thealgorithms/matrix/utils/MatrixUtil.java:34

    private static boolean isValid(final BigDecimal[][] matrix) {
        return matrix != null && matrix.length > 0 && matrix[0].length > 0;
    }

    private static boolean hasEqualSizes(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2) {
        return isValid(matrix1) && isValid(matrix2) && matrix1.length == matrix2.length && matrix1[0].length == matrix2[0].length;
    }

    private static boolean canMultiply(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2) {
        return isValid(matrix1) && isValid(matrix2) && matrix1[0].length == matrix2.length;
    }

    public static void validateInputMatrix(double[][] matrix) {
        if (matrix == null) {
            throw new IllegalArgumentException("The input matrix cannot be null");
        }
        if (matrix.length == 0) {
            throw new IllegalArgumentException("The input matrix cannot be empty");
        }
        if (!hasValidRows(matrix)) {
            throw new IllegalArgumentException("The input matrix cannot have null or empty rows");
        }
        if (isJaggedMatrix(matrix)) {
            throw new IllegalArgumentException("The input matrix cannot be jagged");
        }
    }

    private static boolean hasValidRows(double[][] matrix) {
        for (double[] row : matrix) {
            if (row == null || row.length == 0) {
                return false;
            }
        }
        return true;
    }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Verify the data source yields at least one row before building the matrix.
2. Branch around the operation if an empty matrix is legitimate in your domain.
3. Log matrix.length right before the call to confirm it is zero.

Example fix

// before
double[][] m = rows.toArray(new double[0][]);
MatrixUtil.validateInputMatrix(m); // throws when rows empty

// after
if (rows.isEmpty()) throw new IllegalStateException("No rows to build matrix");
double[][] m = rows.toArray(new double[0][]);
MatrixUtil.validateInputMatrix(m);

if (matrix == null || matrix.length == 0) {
    throw new IllegalStateException("Matrix must have at least one row");
}

static boolean isNonEmptyMatrix(double[][] m) {
    return m != null && m.length > 0;
}

When it happens

Trigger: Passing new double[0][], an empty matrix from a list-to-array conversion with no elements, or a parser that produced no rows from blank input.

Common situations: Empty input file, an upstream filter that removed all rows, or a default-initialized matrix before appending data.

Related errors

• The input matrix cannot be empty
• The input matrix cannot be null
• The input matrix cannot have null or empty rows
• The input matrix cannot be jagged
• The input matrix cannot be null

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/dba9b595dca06909. Report an issue: GitHub.