What is the fundamental requirement of an index when working with arrays?

The fundamental requirement of an index when working with arrays is that it must be a nonnegative integer. In Java, as well as in many programming languages, the indexing of arrays starts from zero, which means the first element of the array is accessed using the index of zero. This leads to the necessity for the index to be nonnegative because negative indices are not valid and will result in runtime errors.

Nonnegative integers encompass all whole numbers starting from zero and going upwards. For instance, if you have an array of size 5, the valid indices are 0, 1, 2, 3, and 4. Using any negative number or any other number that is not an integer (like a decimal point) would not correspond to a valid position in the array, resulting in an ArrayIndexOutOfBoundsException.

The other options do not correctly describe array indexing in Java. The idea that it must always start from one is not accurate, as zero-indexing is a foundational concept in many programming languages, including Java. Saying it should never be zero is also incorrect, as zero is the starting index for the first element of the array. Lastly, allowing any integer would be invalid because negative integers would lead to errors, and thus