didi/DoKit · error · IndexOutOfBoundsException

Index cannot be negative: " + index

Error message

Index cannot be negative: " + index

What it means

CollectionUtils.get(object, index) rejects any negative index immediately with IndexOutOfBoundsException. The method supports Map, List, Object[], Iterator, Collection, Enumeration and reflective arrays, and the negative check runs before any dispatch, so it applies to all of them. This is a strict argument-validation failure, independent of the container's contents.

Source

Thrown at Android/dokit-util/src/main/java/com/didichuxing/doraemonkit/util/CollectionUtils.java:710

     * <li> Collection -- the value returned is the <code>index</code>-th object
     * returned by the collection's default iterator, if there is such an element.</li>
     * <li> Iterator or Enumeration -- the value returned is the
     * <code>index</code>-th object in the Iterator/Enumeration, if there
     * is such an element.  The Iterator/Enumeration is advanced to
     * <code>index</code> (or to the end, if <code>index</code> exceeds the
     * number of entries) as a side effect of this method.</li>
     * </ul>
     *
     * @param object the object to get a value from
     * @param index  the index to get
     * @return the object at the specified index
     * @throws IndexOutOfBoundsException if the index is invalid
     * @throws IllegalArgumentException  if the object type is invalid
     */
    public static Object get(Object object, int index) {
        if (object == null) return null;
        if (index < 0) {
            throw new IndexOutOfBoundsException("Index cannot be negative: " + index);
        }
        if (object instanceof Map) {
            Map map = (Map) object;
            Iterator iterator = map.entrySet().iterator();
            return get(iterator, index);
        } else if (object instanceof List) {
            return ((List) object).get(index);
        } else if (object instanceof Object[]) {
            return ((Object[]) object)[index];
        } else if (object instanceof Iterator) {
            Iterator it = (Iterator) object;
            while (it.hasNext()) {
                index--;
                if (index == -1) {
                    return it.next();
                } else {
                    it.next();
                }

View on GitHub (pinned to 626827cddb)

Solutions

1. Check index >= 0 before calling, returning null or a default when it is not.
2. Never feed an indexOf()/find() result straight in; check for -1 (or use ArrayUtils.INDEX_NOT_FOUND) first.
3. Clamp the index: Math.max(0, Math.min(index, size - 1)) when a boundary element is acceptable.

Example fix

// before
Object prev = CollectionUtils.get(items, currentPosition - 1); // throws at position 0

// after
Object prev = currentPosition > 0
        ? CollectionUtils.get(items, currentPosition - 1)
        : null;

if (index < 0) return null;
return CollectionUtils.get(object, index);

When it happens

Trigger: Passing index < 0, e.g. CollectionUtils.get(list, position - 1) when position == 0; computing an index with Math.round or integer division that can go negative on empty input.

Common situations: RecyclerView/ListView adapter code translating an item position to a collection index; 'previous element' lookups (i - 1) at i == 0; sentinel -1 from indexOf being passed through unchecked.

Related errors

• Entry does not exist: " + index
• Transformation list must not be null.
• maxStoredHeapDumps must be at least 1
• Index: " + index + ", array1 Length: 0
• Index: " + index + ", array1 Length: " + len1

AI-assisted analysis of didi/DoKit@626827cddb (2026-08-14). Data as JSON: /api/errors/9ff5bba24d97f3bf. Report an issue: GitHub.