BQLCompiler.java 文件源码

private static TerminalNode getStartNode(ParseTree tree) {
  if (tree instanceof TerminalNode) {
    return (TerminalNode) tree;
  }

  Deque<ParseTree> workList = new ArrayDeque<ParseTree>();
  IntegerStack workIndexStack = new IntegerStack();
  workList.push(tree);
  workIndexStack.push(0);
  while (!workList.isEmpty()) {
    ParseTree currentTree = workList.peek();
    int currentIndex = workIndexStack.peek();
    if (currentIndex == currentTree.getChildCount()) {
      workList.pop();
      workIndexStack.pop();
      continue;
    }

    // move work list to next child
    workIndexStack.push(workIndexStack.pop() + 1);

    // process the current child
    ParseTree child = currentTree.getChild(currentIndex);
    if (child instanceof TerminalNode) {
      return (TerminalNode) child;
    }

    workList.push(child);
    workIndexStack.push(0);
  }

  return null;
}