Binary Search Tree Iterator

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class BSTIterator {
    PriorityQueue<Integer> vals = new PriorityQueue<Integer>();
    public BSTIterator(TreeNode root) {
        fillPri(root);
    }
    
    /** @return the next smallest number */
    public int next() {
        return vals.poll();
    }
    
    /** @return whether we have a next smallest number */
    public boolean hasNext() {
        if(vals.isEmpty()){
            return false;
        }
        return true;
    }
    public void fillPri(TreeNode root){
        if(root == null){
            return ;
        }
        vals.add(root.val);
        fillPri(root.left);
        fillPri(root.right);
    }
}

/**
 * Your BSTIterator object will be instantiated and called as such:
 * BSTIterator obj = new BSTIterator(root);
 * int param_1 = obj.next();
 * boolean param_2 = obj.hasNext();
 */