1 package hello;
 2 import java.util.*;
 3 
 4 public class TwoStackOneQueue<E> {
 5     private Stack<E> s1 = new Stack<>();
 6     private Stack<E> s2 = new Stack<>();
 7 
 8     public void enqueue(E item){
 9         s1.push(item);
10     }
11 
12     public E dequeue(){
13         if (s2.empty()){
14             if(s1.empty()){
15                 throw new ArrayIndexOutOfBoundsException();
16             }else{
17                 popS1ToS2();
18                 return s2.pop();
19             }
20         }else{
21             return s2.pop();
22         }
23     }
24 
25     private void popS1ToS2(){
26         while(!s1.empty()){
27             s2.push(s1.pop());
28         }
29     }
30 
31     public static void main(String[] args){
32         TwoStackOneQueue<Integer> tsoq = new TwoStackOneQueue<>();
33         for (int i = 0; i < 20; i++){
34             tsoq.enqueue(i);
35         }
36         for (int i = 0; i < 10; i++) {
37             System.out.println(tsoq.dequeue());
38         }
39         for (int i = 20; i < 40; i++){
40             tsoq.enqueue(i);
41         }
42         for (int i = 0; i < 30; i++) {
43             System.out.println(tsoq.dequeue());
44         }
45     }
46 }