TheAlgorithms/Java · error · IllegalArgumentException

Array must be non-empty.

Error message

Array must be non-empty.

What it means

Thrown by FindMaxRecursion.max(int[] array, int low, int high) when array.length is 0. This divide-and-conquer method splits the range [low, high] into halves and recurses, terminating when low == high (returning array[low]). An empty array has no valid element to return. Note: the method checks array.length == 0 but does NOT validate that low/high are within bounds — passing an empty array is the only condition that triggers this specific message.

Source

Thrown at src/main/java/com/thealgorithms/maths/FindMaxRecursion.java:17

package com.thealgorithms.maths;

public final class FindMaxRecursion {

    private FindMaxRecursion() {
    }
    /**
     * Get max of an array using divide and conquer algorithm
     *
     * @param array contains elements
     * @param low the index of the first element
     * @param high the index of the last element
     * @return max of {@code array}
     */
    public static int max(final int[] array, final int low, final int high) {
        if (array.length == 0) {
            throw new IllegalArgumentException("Array must be non-empty.");
        }
        if (low == high) {
            return array[low]; // or array[high]
        }

        int mid = (low + high) >>> 1;

        int leftMax = max(array, low, mid); // get max in [low, mid]
        int rightMax = max(array, mid + 1, high); // get max in [mid+1, high]

        return Math.max(leftMax, rightMax);
    }

    /**
     * Get max of an array using recursion algorithm
     *
     * @param array contains elements
     * @return max value of {@code array}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Ensure array.length > 0 before calling max().
2. Validate that 0 <= low <= high < array.length in addition to non-emptiness.
3. Wrap in a defensive helper that checks both the array and index bounds before delegating.

Example fix

// before
int result = FindMaxRecursion.max(arr, 0, arr.length - 1);

// after
if (arr.length == 0) {
    throw new IllegalArgumentException("Cannot compute max of empty array");
}
if (low < 0 || high >= arr.length || low > high) {
    throw new IndexOutOfBoundsException("Invalid range [" + low + ", " + high + "]");
}
int result = FindMaxRecursion.max(arr, low, high);

if (array == null || array.length == 0) {
    throw new IllegalArgumentException("Array must be non-empty");
}
if (low < 0 || high >= array.length || low > high) {
    throw new IndexOutOfBoundsException("Invalid range [" + low + ", " + high + "]");
}
int result = FindMaxRecursion.max(array, low, high);

static boolean isValidRange(int[] array, int low, int high) {
    return array != null && array.length > 0
        && low >= 0 && high < array.length && low <= high;
}

try {
    int result = FindMaxRecursion.max(array, low, high);
} catch (IllegalArgumentException e) {
    // empty array; handle gracefully
}

When it happens

Trigger: Calling max(new int[0], 0, 0) or max(emptyArray, anyLow, anyHigh). The length check fires regardless of the low/high arguments. Also triggered if low/high are passed as values outside the array bounds without the length being zero (in that case you get a different ArrayIndexOutOfBoundsException, not this message).

Common situations: Passing empty arrays from filtered data. Mismatch between caller-supplied low/high indices and the actual array size. Recursive callers that shrink ranges without checking for emptiness.

Related errors

• array must be non-empty.
• Array must be non-empty.
• Array must be non-empty.
• k must be between 1 and the size of the array
• Input array must have length of at least two

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/89e18c326ed20af5. Report an issue: GitHub.