stanfordnlp/CoreNLP · warning · NoSuchElementException

ArrayCoreMap keySet iterator exhausted

Error message

ArrayCoreMap keySet iterator exhausted

What it means

ArrayCoreMap's keySet iterator converts an ArrayIndexOutOfBoundsException from indexing past the internal keys array into a NoSuchElementException with this message. It is the standard Iterator contract: calling next() after the last key throws. The message is only a diagnostic rethrow, not a corruption indicator.

Solutions

1. Use a for-each loop over coremap.keySet() instead of manual next() calls.
2. Always check hasNext() before next().
3. Avoid removing keys from the ArrayCoreMap while iterating over its key set.
4. If index-based access is needed, bounds-check against size() first.

Example fix

// before
Iterator<Class<?>> it = map.keySet().iterator();
while (true) { process(it.next()); } // throws at end
// after
for (Class<?> key : map.keySet()) { process(key); }

try { Class<?> k = it.next(); } catch (NoSuchElementException e) { /* iterator exhausted: normal end-of-iteration signal */ }

When it happens

Trigger: Calling next() on the keySet()/keyIterator() of an ArrayCoreMap after hasNext() would return false — i.e. iterating past the end, including concurrent modification that shrinks the map while iterating.

Common situations: Manual index-based loops over keys without checking i < size(); nested iteration that removes keys mid-loop; forgetting hasNext() when consuming the iterator directly.

Related errors

• DocumentIterator exhausted.
• Processed trees, but there are more trees and text is empty
• DocumentIterator exhausted.
• Graph edge iterator exhausted.
• ERROR: Sentences must instantiate Annotation!

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/e1b3e39ede96e118. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/ArrayCoreMap.java:178

  public Set<Class<?>> keySet() {

    return new AbstractSet<Class<?>>() {
      @Override
      public Iterator<Class<?>> iterator() {
        return new Iterator<Class<?>>() {
          private int i; // = 0;

          @Override
          public boolean hasNext() {
            return i < size;
          }

          @Override
          public Class<?> next() {
            try {
              return keys[i++];
            } catch (ArrayIndexOutOfBoundsException aioobe) {
              throw new NoSuchElementException("ArrayCoreMap keySet iterator exhausted");
            }
          }

          @Override
          @SuppressWarnings("unchecked")
          public void remove() {
            ArrayCoreMap.this.remove((Class) keys[i]);
          }
        };
      }

      @Override
      public int size() {
        return size;
      }
    };
  }

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