javapublic static void postOrderNonrecur(Treenode rootnode){ if(rootnode==null){ return; } Stack stack = new Stack(); Treenode current = rootnode; while(current !=null || stack.isEmpty()!=true){ //step 1 while(current!=null){ if(current.rightchild!=null){ stack.push(current.rightchild); } stack.push(current); current = current.leftchild; } current = stack.pop(); if(current.rightchild!=null && current.rightchild == stack.peek() ){ System.out.println("here"); stack.pop(); //出栈右孩子 stack.push(current); current = current.rightchild; } else{ System.out.println(current.value); current = null; } } }

测试用例是

出错是：
Exception in thread "main" 4
7
8
6
12
16
14
java.util.EmptyStackException
at java.util.Stack.peek(Unknown Source)
at gsm.Tree.postOrderNonrecur(Tree.java:110)
at gsm.Tree.main(Tree.java:140)
请问代码哪里出错了？