Binary Search Tree Iterator

自己能不能不要总犯下面那种那么2的错误。。

嫩不能尽量明白，自己写的每段code是做啥的，能负责任！！！

/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/

public class BSTIterator {

Stack<TreeNode> stack;
public BSTIterator(TreeNode root) {
stack = new Stack<>();
TreeNode node = root;
while (node != null) {
stack.push(node);
node = node.left;
}
}

/** @return whether we have a next smallest number */
public boolean hasNext() {
//return stack.isEmpty();
return !stack.isEmpty();
}

/** @return the next smallest number */
public int next() {
TreeNode smallest = stack.pop();
if (smallest.right != null) {
TreeNode node = smallest.right;
while (node != null) {
stack.push(node);
node = node.left;
}
}
return smallest.val;
}
}

/**
* Your BSTIterator will be called like this:
* BSTIterator i = new BSTIterator(root);
* while (i.hasNext()) v[f()] = i.next();
*/