Arrays.fill() methods that fill an entire array, e.g.,

    public static void fill(long[] a, long val) {
        fill(a, 0, a.length, val);
    }

call the from/to-index form, e.g.,

    public static void fill(long[] a, int fromIndex, int toIndex, long val) {
        rangeCheck(a.length, fromIndex, toIndex);
        for (int i=fromIndex; i<toIndex; i++)
            a[i] = val;
    }

which call rangeCheck(), vis,

    private static void rangeCheck(int arrayLen, int fromIndex, int toIndex) {
        if (fromIndex > toIndex)
            throw new IllegalArgumentException("fromIndex(" + fromIndex +
                       ") > toIndex(" + toIndex+")");
        if (fromIndex < 0)
            throw new ArrayIndexOutOfBoundsException(fromIndex);
        if (toIndex > arrayLen)
            throw new ArrayIndexOutOfBoundsException(toIndex);
    }

When filling an entire array, none of the exceptions in rangeCheck can happen,
because fromIndex == 0 and toIndex == arrayLen and is always >= 0.

For these fill() methods, the call to rangeCheck can be elided.