TheAlgorithms/Java · error · IllegalArgumentException

Position must be between 0 and {array.length}

Error message

Position must be between 0 and {array.length}

What it means

Thrown by InsertDeleteInArray.insertElement when the requested insertion position is outside the valid inclusive range [0, array.length]. The library enforces this so that System.arraycopy never reads out of bounds and the returned array stays well-formed. The message appends the actual array length so the caller sees the accepted upper bound.

Source

Thrown at src/main/java/com/thealgorithms/others/InsertDeleteInArray.java:60

     * Creates a new array with size = original array size + 1.
     * Elements at positions <= insertPos retain their positions,
     * while elements at positions > insertPos are shifted right by one position.
     * </p>
     *
     * @param array    the original array
     * @param element  the element to be inserted
     * @param position the index at which the element should be inserted (0-based)
     * @return a new array with the element inserted at the specified position
     * @throws IllegalArgumentException if position is negative or greater than
     *                                  array length
     * @throws IllegalArgumentException if array is null
     */
    public static int[] insertElement(int[] array, int element, int position) {
        if (array == null) {
            throw new IllegalArgumentException("Array cannot be null");
        }
        if (position < 0 || position > array.length) {
            throw new IllegalArgumentException("Position must be between 0 and " + array.length);
        }

        int[] newArray = new int[array.length + 1];

        // Copy elements before insertion position
        System.arraycopy(array, 0, newArray, 0, position);

        // Insert the new element
        newArray[position] = element;

        // Copy remaining elements after insertion position
        System.arraycopy(array, position, newArray, position + 1, array.length - position);

        return newArray;
    }

    /**
     * Deletes an element at the specified position from the array.

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Clamp or validate position to [0, array.length] before calling insertElement.
2. If you meant to append, pass position = array.length explicitly.
3. Re-derive the index from the same array instance you pass in, not a stale copy.
4. Sanitize external/user input (round, bound, reject) before it reaches this method.

Example fix

// before
int[] out = InsertDeleteInArray.insertElement(arr, val, arr.length + 1); // throws

// after
int pos = Math.max(0, Math.min(position, arr.length));
int[] out = InsertDeleteInArray.insertElement(arr, val, pos);

public static int safePosition(int[] array, int requested) {
    if (array == null) throw new IllegalArgumentException("array is null");
    return Math.max(0, Math.min(requested, array.length));
}
// usage:
InsertDeleteInArray.insertElement(arr, val, safePosition(arr, requested));

public static boolean isValidInsertPosition(int[] array, int position) {
    return array != null && position >= 0 && position <= array.length;
}

try {
    out = InsertDeleteInArray.insertElement(arr, val, pos);
} catch (IllegalArgumentException e) {
    // log pos and arr.length, fall back to appending at the end
    out = InsertDeleteInArray.insertElement(arr, val, arr.length);
}

When it happens

Trigger: Calling insertElement(array, element, position) with position < 0 or position > array.length. Inserting at exactly array.length IS allowed (appends); anything beyond it is rejected.

Common situations: Off-by-one from treating the valid insert slot as array.length-1 (forgetting append is legal); passing a position computed from a different/older array length; user-supplied index parsed from input without clamping; negative index coming from an arithmetic underflow.

Related errors

• Position must be between 0 and + (array.length - 1)
• Array is empty
• Node index out of bounds
• width and height must be > 0
• Key must contain integers from 1 to {}

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/8558ecf484d257df. Report an issue: GitHub.