剑指offer——用两个栈实现队列

import java.util.Stack;
 
public class Solution {
    Stack<Integer> stack1 = new Stack<Integer>();
    Stack<Integer> stack2 = new Stack<Integer>();
     
    public void push(int node) {
        stack1.push(node);
    }
     
    public int pop() throws Exception{
        if(stack2.isEmpty()){
            while(!stack1.isEmpty()){
                stack2.push(stack1.pop());
            }
        }
        if(stack2.isEmpty()){
            throw new Exception("stack1 is empty");
        }
        return stack2.pop();
    }
}