{"record":{"id":"617b2b100f93b7c9","repo":"TheAlgorithms/Java","slug":"invalid-input-parameters","errorCode":null,"errorMessage":"Invalid input parameters","messagePattern":"Invalid input parameters","errorType":"exception","errorClass":"IllegalArgumentException","httpStatus":null,"severity":"error","filePath":"src/main/java/com/thealgorithms/randomized/MonteCarloIntegration.java","lineNumber":65,"sourceCode":"\n    /**\n     * Approximates the definite integral of a given function over a specified\n     * interval using the Monte Carlo method with a random seed based on the\n     * current system time for more randomness.\n     *\n     * @param fx    the function to integrate\n     * @param a     the lower bound of the interval\n     * @param b     the upper bound of the interval\n     * @param n     the number of random samples to use\n     * @return      the approximate value of the integral\n     */\n    public static double approximate(Function<Double, Double> fx, double a, double b, int n) {\n        return doApproximate(fx, a, b, n, new Random(System.currentTimeMillis()));\n    }\n\n    private static double doApproximate(Function<Double, Double> fx, double a, double b, int n, Random generator) {\n        if (!validate(fx, a, b, n)) {\n            throw new IllegalArgumentException(\"Invalid input parameters\");\n        }\n        double total = 0.0;\n        double interval = b - a;\n        int pairs = n / 2;\n        for (int i = 0; i < pairs; i++) {\n            double u = generator.nextDouble();\n            double x1 = a + u * interval;\n            double x2 = a + (1.0 - u) * interval;\n            total += fx.apply(x1);\n            total += fx.apply(x2);\n        }\n        if ((n & 1) == 1) {\n            double x = a + generator.nextDouble() * interval;\n            total += fx.apply(x);\n        }\n        return interval * total / n;\n    }\n","sourceCodeStart":47,"sourceCodeEnd":83,"githubUrl":"https://github.com/TheAlgorithms/Java/blob/fdfb9a395b310167a66bd29e311e36e0e3e9b964/src/main/java/com/thealgorithms/randomized/MonteCarloIntegration.java#L47-L83","documentation":"Thrown by MonteCarloIntegration.approximate/doApproximate when validate() fails. validate() requires ALL of: fx != null, a < b (strict — a == b is invalid), and n > 0. The single generic message hides which condition failed, so you must check all three.","triggerScenarios":"approximate(null, 0, 1, 100) (null function); approximate(f, 2, 1, 100) (a >= b); approximate(f, 0, 1, 0) (n <= 0); approximate(f, 0, 0, 10) (degenerate zero-width interval).","commonSituations":"Passing bounds in the wrong order (upper as lower); defaulting sample count to 0 in a config; a null Function reference when the integrand wasn't set; flipping a/b when integrating a descending interval.","solutions":["Ensure the integrand fx is a non-null Function<Double,Double> before calling.","Pass bounds with a < b strictly; if your interval is [b, a] with b > a, swap them (or negate the result).","Pass a positive sample count n (e.g. 1000 or more for usable accuracy)."],"exampleFix":"// before\nMonteCarloIntegration.approximate(fx, upper, lower, 0); // bounds reversed, n=0\n\n// after\ndouble lo = Math.min(upper, lower);\ndouble hi = Math.max(upper, lower);\ndouble result = (fx != null && hi > lo && samples > 0)\n    ? MonteCarloIntegration.approximate(fx, lo, hi, samples)\n    : Double.NaN;","handlingStrategy":"validation","validationCode":"if (fx == null || !(a < b) || n <= 0) {\n    throw new IllegalArgumentException(\"fx must be non-null, a < b, n > 0\");\n}\ndouble approx = MonteCarloIntegration.approximate(fx, a, b, n);","typeGuard":"static boolean validMonteCarlo(Function<Double,Double> fx, double a, double b, int n) {\n    return fx != null && a < b && n > 0;\n}","tryCatchPattern":"try {\n    double approx = MonteCarloIntegration.approximate(fx, a, b, n);\n} catch (IllegalArgumentException e) {\n    // message is generic; re-check fx/a/b/n yourself to report the real cause\n    logger.warn(\"Monte Carlo rejected params: fx={}, a={}, b={}, n={}\", fx != null, a, b, n);\n}","preventionTips":["The exception message gives no detail — validate all three conditions yourself for a clear error.","Always pass a < b strictly; swap bounds (and negate the result) for descending intervals.","Use a non-trivial sample count (1000+) for usable accuracy; never default n to 0."],"tags":["randomized","monte-carlo","input-validation","illegal-argument","generic-message"],"backgroundTag":null,"analyzedSha":"fdfb9a395b310167a66bd29e311e36e0e3e9b964","analyzedAt":"2026-08-13T23:36:13.315Z","schemaVersion":2},"datasetVersion":"2026-08-14T00:17:13.853Z"}