剑指Offer07-两个栈实现队列

import java.util.Stack;

public class No7 {

    public static void main(String[] args) {
        No7 queue = new No7();
        queue.offer(1);
        queue.offer(2);
        queue.offer(3);
        queue.poll();
        queue.poll();
        queue.poll();
    }
    
    private Stack s1 = new Stack();
    private Stack s2 = new Stack();
    //实现队列的的offer方法：将元素加入到队列的末尾
    public void offer(Object x) {
        s1.push(x);
    }
    
    public void poll() {
        if(s1.size()==0 && s2.size()==0 ) {
            
            try {
                throw new Exception("队列为空");
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        else {
            if(s2.size()!=0) {
                System.out.println(s2.peek().toString());
                s2.pop();
            }
            else {
                //将s1的数据赋值给s2
                while(s1.size()>0) {
                    s2.push(s1.pop());
                }
                System.out.println(s2.peek().toString());
                s2.pop();
            }
        }
    }

}