stanfordnlp/CoreNLP · error · IllegalStateException

Old root not a child of it's parent

Error message

Old root not a child of it's parent

What it means

rightRotate moves oldRoot down to the left and its left child up. After rotating, if the new root still has a parent, that parent's child pointer must reference oldRoot before the rotation so it can be swapped to newRoot; if neither parent.left nor parent.right equals oldRoot, the tree linkage is inconsistent and the library throws instead of silently corrupting the tree.

Solutions

1. Avoid direct manipulation of IntervalTree internals; use add/remove API
2. Verify parent/child back-pointers are symmetric before invoking rotation helpers
3. Rebuild the tree from its elements to restore invariants
4. File a bug with reproduction if reachable via public API

Example fix

// before
someNode.parent = p; // p.left/right not updated
IntervalTree.Node r = tree.rightRotate(someNode); // throws
// after
// reattach via the tree API so p.left/right and someNode.parent stay consistent

if (newRoot.parent != null && newRoot.parent.left != oldRoot && newRoot.parent.right != oldRoot) {
  throw new IllegalStateException("rotation precondition violated");
}
Node r = tree.rightRotate(oldRoot);

boolean isChildOfParent(Node oldRoot) {
  return oldRoot.parent == null || oldRoot.parent.left == oldRoot || oldRoot.parent.right == oldRoot;
}

try {
  Node r = tree.rightRotate(node);
} catch (IllegalStateException e) {
  // restore via rebuild; do not continue with corrupted tree
  tree = rebuildFromElements(elements);
}

When it happens

Trigger: Calling rightRotate on a node whose parent pointer is stale or whose parent's child pointers no longer reference it — typically after manual node mutation or an out-of-band structural change.

Common situations: Hand-written tree surgery, subclass overrides, or debugging experiments that detach/reattach nodes without updating the symmetric pointer.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

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• allSentences != allWords
• Error -- attempt to operate with key of wrong length…
• Error: cannot insert multiple keys with the same value
• mapDependencies: HeadFinder failed!

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/66e41f44a390c5f4. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/IntervalTree.java:498

    if (oldRoot == null || oldRoot.isEmpty() || oldRoot.left == null) return oldRoot;

    TreeNode<E,T> oldLeftRight = oldRoot.left.right;

    TreeNode<E,T> newRoot = oldRoot.left;
    newRoot.right = oldRoot;
    oldRoot.left = oldLeftRight;

    // Adjust parents and such
    newRoot.parent = oldRoot.parent;
    newRoot.maxEnd = oldRoot.maxEnd;
    newRoot.size = oldRoot.size;
    if (newRoot.parent != null) {
      if (newRoot.parent.left == oldRoot) {
        newRoot.parent.left = newRoot;
      } else if (newRoot.parent.right == oldRoot) {
        newRoot.parent.right = newRoot;
      } else {
        throw new IllegalStateException("Old root not a child of it's parent");
      }
    }

    oldRoot.parent = newRoot;
    if (oldLeftRight != null) oldLeftRight.parent = oldRoot;
    adjust(oldRoot);
    return newRoot;
  }

  // Moves this node to the left and the right child up and returns the new root
  public TreeNode<E,T> leftRotate(TreeNode<E,T> oldRoot) {
    if (oldRoot == null || oldRoot.isEmpty() || oldRoot.right == null) return oldRoot;

    TreeNode<E,T> oldRightLeft = oldRoot.right.left;

    TreeNode<E,T> newRoot = oldRoot.right;
    newRoot.left = oldRoot;
    oldRoot.right = oldRightLeft;

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