用两个栈实现队列（完整代码用Java语言实现）

package com.jzoffer.stackandqueue;

import java.util.Scanner;
import java.util.Stack;



class CQueue {
    private Stack stack1;
    private Stack stack2;
    public CQueue() {
        this.stack1 = new Stack<>();
        this.stack2 = new Stack<>();
    }

    public void appendTail(int value) {
        while (!stack2.isEmpty()) {
            stack1.push(stack2.pop());
        }
        stack1.push(value);
    }

    public int deleteHead() {
        while (!stack1.isEmpty()) {
            stack2.push(stack1.pop());
        }
        if (stack2.isEmpty()) {
            System.out.println("队列为空");
            return -1;
        }
        System.out.printf("队首元素%d已删除",stack2.peek());
        System.out.println();
        return stack2.pop();
    }

    public void showQueue() {
        while (!stack1.isEmpty()) {
            stack2.push(stack1.pop());//如果栈1非空，那么要将栈1中的元素转移到栈2，再输出
        }
        if (stack2.isEmpty()) {
            System.out.println("队列为空");
        }

        if (!stack2.isEmpty()) {
            System.out.println("队列如下（队首---队尾）");
            for (int index = stack2.size() - 1; index >= 0; index--) {
                System.out.printf("%d   ", stack2.get(index));
            }
            System.out.println();
        }
    }
}

public class CQueueDemo {
    public static void main(String[] args) {
        CQueue q = new CQueue();
        Scanner in = new Scanner(System.in);
        char key = ' ';
        boolean loop = true;
        while (loop) {
            System.out.println("a---添加元素");
            System.out.println("d---删除队首元素");
            System.out.println("s---显示队列");
            System.out.println("q---退出");
            System.out.println("请选择操作:");
            key = in.next().charAt(0);
            switch (key) {
                case 'a' :
                    System.out.println("请输入一个数字");
                    int val = in.nextInt();
                    q.appendTail(val);
                    break;
                case 'd' :
                    q.deleteHead();
                    break;
                case 's' :
                    q.showQueue();
                    break;
                case 'q' :
                    loop = false;
                    break;
                default:
                    break;
            }
        }
        in.close();
    }
}