stanfordnlp/CoreNLP · error · IllegalStateException

Not on parent's left or right branches.

Error message

Not on parent's left or right branches.

What it means

IntervalTree.rotateUp walks up the tree splaying/rotating nodes toward the root. Each node must be linked to its parent via the parent's left or right child pointer; if a node's parent reference is set but the parent does not point back to it, the tree's link invariants are broken and the library refuses to guess a rotation direction.

Solutions

1. Do not mutate IntervalTree node parent/left/right fields directly; only use the public add/remove/query API
2. Rebuild the tree from its elements if corruption is suspected (new IntervalTree + re-add all values)
3. Check any overridden or wrapped IntervalTree operations for missed adjust()/parent reassignment steps
4. Report the bug with a minimal reproduction if it occurs through public API only

Example fix

// before: manual mutation
node.parent.left = otherNode; // breaks back-pointer, rotateUp throws
// after
intervalTree.remove(node.value);
intervalTree.add(otherValue); // let the tree maintain invariants

if (n.parent == null || (n.parent.left != n && n.parent.right != n)) {
  throw new IllegalStateException("node not linked to parent; tree corrupted");
}
tree.rotateUp(n); // safe

boolean isLinkedToParent(Node n) {
  return n.parent != null && (n.parent.left == n || n.parent.right == n);
}

try {
  tree.rotateUp(node);
} catch (IllegalStateException e) {
  // tree invariants broken: rebuild
  tree = rebuildFromElements(elements);
}

When it happens

Trigger: Calling rotateUp (directly or via balance) on a node whose parent pointer is non-null but whose parent's left/right references were corrupted by manual mutation of IntervalTree nodes, incorrect custom rebalancing, or a stale parent reference after an out-of-band remove.

Common situations: Custom code poking at the internal node fields, subclassing IntervalTree and overriding adjust/remove, or a bug in another operation that left parent/child pointers asymmetric.

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

• Old root not a child of it's parent
• allSentences != allWords
• Empty node shouldn't have left branch
• Empty node shouldn't have right branch
• Error -- attempt to operate with key of wrong length…

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/c9ad0837c7def604. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/IntervalTree.java:472

      if (median.right != null) todo.push(median.right);
    }
    if (newRoot == null) return node;
    else return newRoot;
  }

  // Moves this node up the tree until it replaces the target node
  public void rotateUp(TreeNode<E,T> node, TreeNode<E,T> target) {
    TreeNode<E,T> n = node;
    boolean done = false;
    while (n != null && n.parent != null && !done) {
      // Check if we are the left or right child
      done = (n.parent == target);
      if (n == n.parent.left) {
        n = rightRotate(n.parent);
      } else if (n == n.parent.right) {
        n = leftRotate(n.parent);
      } else {
        throw new IllegalStateException("Not on parent's left or right branches.");
      }
      if (debug) check(n);
    }
  }

  // Moves this node to the right and the left child up and returns the new root
  public TreeNode<E,T> rightRotate(TreeNode<E,T> oldRoot) {
    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;

View on GitHub (pinned to 1b7edd19c4)