The annotated expression is between -1 and -a.length - 1, inclusive, for each sequence a listed in the annotation.

This type should rarely (if ever) be written by programmers. It is inferred by the SearchIndexChecker when the result of a call to one of the JDK's binary search methods (like Arrays.binarySearch) is known to be less than zero. For example, consider the following code:

    int index = Arrays.binarySearch(array, target);
    if (index < 0) {
         // index's type here is @NegativeIndexFor("array")
         index = index * -1;
         // now index's type is @IndexFor("array")
    }