TheAlgorithms/Java · error · IllegalArgumentException

The input matrix cannot be null

Error message

The input matrix cannot be null

What it means

Thrown by MatrixUtil.validateInputMatrix (the double[][] overload) when the matrix argument is null. MatrixUtil also handles BigDecimal matrices via separate helpers; this validator guards the primitive double matrix path. A null matrix has no dimensions or rows for subsequent hasValidRows/isJaggedMatrix checks, so it is rejected first.

Source

Thrown at src/main/java/com/thealgorithms/matrix/utils/MatrixUtil.java:31

    private MatrixUtil() {
    }

    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;
            }
        }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Ensure the double[][] is instantiated before calling MatrixUtil.
2. Fix the upstream null-return path in the data source.
3. Add an early null guard at the call site with a context-specific message.

Example fix

// before
double[][] a = readMatrix(file);
MatrixUtil.validateInputMatrix(a); // throws if readMatrix returned null

// after
double[][] a = readMatrix(file);
if (a == null) throw new IllegalStateException("Matrix missing for " + file);
MatrixUtil.validateInputMatrix(a);

Objects.requireNonNull(matrix, "matrix");
MatrixUtil.validateInputMatrix(matrix);

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

When it happens

Trigger: Calling a MatrixUtil operation with a double[][] that is null — e.g., a result of a method returning null on error, a field never assigned, or a deserialized object missing its matrix field.

Common situations: Upstream data source returns null on missing input, refactoring dropped the assignment, or a null propagated through a chain of operations.

Related errors

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

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/f1b3bac5d96d5647. Report an issue: GitHub.