stanfordnlp/CoreNLP · error · UnsupportedOperationException

Can only set spans on trees which use CoreLabel

Error message

Can only set spans on trees which use CoreLabel

What it means

Tree.setSpans() annotates every node with its token span via CoreAnnotations.SpanAnnotation, which requires each node's label to be a CoreLabel. In constituentsNodes (leaf case) a label that is not a CoreLabel cannot hold the annotation, so the library throws UnsupportedOperationException.

Solutions

1. Rebuild or re-label the tree using CoreLabel instances: use a TreeFactory with CoreLabelFactory / LabeledScoredTreeFactory(CoreLabelFactory.instance()) so all labels are CoreLabels
2. Convert labels via setLabel(new CoreLabel(...)) for every node, copying the value into the CoreLabel, before calling setSpans
3. Read the tree with TreeReader that specifies CoreLabel as the label type, then call setSpans

Example fix

// before: StringLabel leaves
TreeFactory tf = new TreeFactory(StringLabel.factory());
tree.setSpans(); // throws
// after
TreeFactory tf = new TreeFactory(CoreLabel.factory());
tree.setSpans(); // OK

boolean allCoreLabels = true; for (Tree t : tree) { if (!(t.label() instanceof CoreLabel)) { allCoreLabels = false; break; } }

boolean canSetSpans(Tree t) { return t.getLeaves().stream().allMatch(l -> l.label() instanceof CoreLabel); }

try { tree.setSpans(); } catch (UnsupportedOperationException e) { tree = relabelWithCoreLabels(tree); tree.setSpans(); }

When it happens

Trigger: Calling tree.setSpans() on a tree whose leaf labels are not CoreLabel instances (e.g. StringLabel, WordTag, IndexedWord), which reaches the leaf branch of constituentsNodes.

Common situations: Parsing trees from string formats with a default (non-CoreLabel) TreeReader/label factory, then calling span-dependent methods; mixing trees built with TreeFactory(StringLabel) into CoreNLP annotation pipelines.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Cannot set from string
• : Does not support parse operation.
• CORE: CoreLabel.initFromStrings: Can't handle
• CORE: CoreLabel.initFromStrings: Bad type for…
• This code branch left blank because we do not understand…

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/55ef910f13840fc1. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/trees/Tree.java:552

  public Set<Constituent> constituents(ConstituentFactory cf, boolean charLevel, Predicate<Tree> filter) {
    Set<Constituent> constituentsSet = Generics.newHashSet();
    constituents(constituentsSet, 0, cf, charLevel, filter, -1, 0);
    return constituentsSet;
  }

  /**
   * Same as int constituents but just puts the span as an IntPair
   * in the CoreLabel of the nodes.
   *
   * @param left The left position to begin labeling from
   * @return The index of the right frontier of the constituent
   */
  private int constituentsNodes(int left) {
    if (isLeaf()) {
      if (label() instanceof CoreLabel) {
        ((CoreLabel) label()).set(CoreAnnotations.SpanAnnotation.class, new IntPair(left, left));
      } else {
        throw new UnsupportedOperationException("Can only set spans on trees which use CoreLabel");
      }
      return (left + 1);
    }
    int position = left;

    // enumerate through daughter trees
    Tree[] kids = children();
    for (Tree kid : kids)
      position = kid.constituentsNodes(position);

    //Parent span
    if (label() instanceof CoreLabel) {
      ((CoreLabel) label()).set(CoreAnnotations.SpanAnnotation.class, new IntPair(left, position - 1));
    } else {
      throw new UnsupportedOperationException("Can only set spans on trees which use CoreLabel");
    }

    return position;

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