stanfordnlp/CoreNLP · error · IllegalArgumentException

t insert tree after the

Error message

t insert tree after the 

What it means

Thrown by Tree.insertDtr(Tree dtr, int position) when the requested insertion position is greater than the current number of daughters. The tree has only kids.length children, so a position beyond that (only position == kids.length, append at end, is legal) is invalid.

Solutions

1. Clamp the position: call insertDtr(dtr, Math.min(position, children().length)).
2. Verify the daughter count with tree.children().length before inserting.
3. Recompute the position against the current tree rather than a cached one.

Example fix

// before
tree.insertDtr(newNode, idx);
// after
tree.insertDtr(newNode, Math.min(idx, tree.children().length));

if (position < 0 || position > tree.children().length) throw new IllegalArgumentException("invalid insert position");
tree.insertDtr(dtr, position);

try { tree.insertDtr(dtr, position); } catch (IllegalArgumentException e) { /* clamp and retry */ tree.insertDtr(dtr, tree.children().length); }

When it happens

Trigger: Calling tree.insertDtr(dtr, position) with position > tree.children().length, e.g. computing the index from a stale or differently-sized daughter array, or appending with position = kids.length + 1 instead of kids.length.

Common situations: Programmatic tree rewriting in parsers/annotators that insert nodes; off-by-one errors when the daughter list changed since the position was computed; using 1-based indices in a 0-based API.

Related errors

• Error -- tree does not contain
• Tree is not a descendant of root.
• ancestor: height cannot be negative
• Attempt to open file with null name
• Bad arguments: " + x + " and " + lambda

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/b3b59defb55e8e2d. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/trees/Tree.java:2669

   */
  public List<Tree> siblings(Tree root) {
    Tree parent = parent(root);
    if (parent == null) {
      return null;
    }
    List<Tree> siblings = parent.getChildrenAsList();
    siblings.remove(this);
    return siblings;
  }

  /**
   * insert {@code dtr} after {@code position} existing
   * daughters in {@code this}.
   */
  public void insertDtr(Tree dtr, int position) {
    Tree[] kids = children();
    if (position > kids.length) {
      throw new IllegalArgumentException("Can't insert tree after the " + position + "th daughter in " + this + "; only " + kids.length + " daughters exist!");
    }
    Tree[] newKids = new Tree[kids.length + 1];
    int i = 0;
    for (; i < position; i++) {
      newKids[i] = kids[i];
    }
    newKids[i] = dtr;
    for (; i < kids.length; i++) {
      newKids[i + 1] = kids[i];
    }
    setChildren(newKids);
  }

  // --- composition methods to implement Label interface

  @Override
  public String value() {
    Label lab = label();

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