TheAlgorithms/Java · error · IllegalArgumentException

Input array must have length of at least two

Error message

Input array must have length of at least two

What it means

Thrown by SecondMinMax.findSecondMin / findSecondMax (via private checkInput) when the supplied int[] has fewer than 2 elements. A second-smallest or second-largest value is mathematically undefined for a 0- or 1-element array, so the method refuses to return a meaningless sentinel.

Source

Thrown at src/main/java/com/thealgorithms/maths/SecondMinMax.java:51

    /**
     * @brief Finds the Second minimum / maximum value from the array
     * @param arr the input array
     * @exception IllegalArgumentException => if input array is of length less than 2 also if all elements are same
     * @return the second minimum / maximum value from the input array
     * @author Bharath Sanjeevi ( https://github.com/BharathSanjeeviT )
     */

    public static int findSecondMin(final int[] arr) {
        return secondBest(arr, Integer.MAX_VALUE, (a, b) -> a < b);
    }

    public static int findSecondMax(final int[] arr) {
        return secondBest(arr, Integer.MIN_VALUE, (a, b) -> a > b);
    }

    private static void checkInput(final int[] arr) {
        if (arr.length < 2) {
            throw new IllegalArgumentException("Input array must have length of at least two");
        }
    }

    private static void checkOutput(final int secNum, final int initialVal) {
        if (secNum == initialVal) {
            throw new IllegalArgumentException("Input array should have at least 2 distinct elements");
        }
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Guard the call site: only invoke findSecondMin/findSecondMax when arr.length >= 2.
2. Fix the upstream data source so it actually supplies >= 2 elements.
3. Return an Optional<Integer> from a wrapper if 'no second value' is a legitimate business state.

Example fix

// before
int second = SecondMinMax.findSecondMin(arr);

// after
if (arr == null || arr.length < 2) {
    throw new IllegalArgumentException("Need at least 2 elements, got " + (arr == null ? 0 : arr.length));
}
int second = SecondMinMax.findSecondMin(arr);

if (arr == null || arr.length < 2) {
    throw new IllegalArgumentException("Need >= 2 elements");
}
int s = SecondMinMax.findSecondMin(arr);

try {
    int s = SecondMinMax.findSecondMin(arr);
} catch (IllegalArgumentException e) {
    return OptionalInt.empty();
}

When it happens

Trigger: Call findSecondMin(new int[]{5}), findSecondMax(new int[]{}), or pass an array whose length was derived from an empty collection via stream/mapToInt without a size check.

Common situations: Processing a list that the caller assumed had multiple entries (e.g., results of a filter that returned one match), deserializing JSON into an array that arrived empty, or test data with a single fixture.

Related errors

• k must be between 1 and the size of the array
• Array must be non-empty.
• Array must be non-empty.
• Array must be non-empty.
• array must be non-empty.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/86abb755901260f3. Report an issue: GitHub.