stanfordnlp/CoreNLP · error · IllegalStateException

node is not parent's left or right child!!!

Error message

node is not parent's left or right child!!!

What it means

While validating ordering, check() walks from a node up through n.parent and asserts n is either n.parent.left or n.parent.right. If it is neither, this IllegalStateException fires: the node is unreachable as a proper child of its claimed parent, i.e. the tree's parent/child links are torn. This is a catch-all corruption detector in the validator, thrown as an internal invariant failure.

Solutions

1. Rebuild the IntervalTree from scratch and re-insert all intervals.
2. Never modify TreeNode parent/left/right pointers outside the library's own algorithms.
3. Serialize all access to the tree (no internal thread safety) to avoid interleaved structural updates.
4. Capture a minimal insert/remove/rotate sequence and report it to Stanford CoreNLP if reproducible via public API.

try {
  tree.check(tree.root);
} catch (IllegalStateException e) {
  // ancestry chain broken -> rebuild from source intervals
}

try {
  intervalTree.remove(iv, v);
  intervalTree.check(intervalTree.root);
} catch (IllegalStateException e) {
  intervalTree = rebuildTree(intervals);
}

When it happens

Trigger: check() (or balance()/rotateUp()) climbs an ancestry chain and reaches a node whose parent pointer exists but whose parent's left/right fields don't include it — after a rotation spliced pointers incorrectly or a remove left a phantom parent link.

Common situations: Hit during CoreNLP interval-tree debugging after failed rotations; after concurrent unsynchronized insert/remove; after external code or custom subclasses re-linking nodes.

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

• node left parent is not same as node!!!
• node right parent is not same as node!!!
• Empty node shouldn't have left branch
• Empty node shouldn't have right branch
• max end is not as expected!!!

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/e15a8987dabd87b1. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/IntervalTree.java:411

      if (node.parent != null) {
        // Go up parent and make sure we are on correct side
        TreeNode<E,T> n = node;
        while (n != null && n.parent != null) {
          // Check we are either right or left
          if (n == n.parent.left) {
            // Check that node is less than the parent
            if (node.value != null) {
              if (node.value.getInterval().compareTo(n.parent.value.getInterval()) > 0) {
                throw new IllegalStateException("node is not on the correct side!!!");
              }
            }
          } else if (n == n.parent.right) {
            // Check that node is greater than the parent
            if (node.value.getInterval().compareTo(n.parent.value.getInterval()) <= 0) {
              throw new IllegalStateException("node is not on the correct side!!!");
            }
          } else {
            throw new IllegalStateException("node is not parent's left or right child!!!");
          }
          n = n.parent;
        }
      }
      if (node.left != null) todo.add(node.left);
      if (node.right != null) todo.add(node.right);
    }
  }


  public boolean isAlphaBalanced(TreeNode<E,T> node, double alpha) {
    int leftSize = (node.left != null)? node.left.size:0;
    int rightSize = (node.right != null)? node.right.size:0;
    int threshold = (int) (alpha*node.size) + 1;
    return (leftSize <= threshold) && (rightSize <= threshold);
  }

  public void balance() {

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