两个栈实现一个队列

import java.util.Stack;public class Demo07 {Stack<Integer> stack1 = new Stack<Integer>();Stack<Integer> stack2 = new Stack<Integer>();public void push(int node) {stack1.push(node);}public int pop() {if(stack2.size()<=0){while(stack1.size()>0){/*int data = stack1.peek();//查看栈顶元素，但不移除它stack1.pop();//弹出栈顶元素stack2.push(data);//压入*/                             stack2.push(stack1.pop());}}if(stack2.isEmpty()){try {throw new Exception("queue is empty.");} catch (Exception e) {}}/*** int head = stack2.peek();* stack2.pop();*/int head = stack2.pop();return head;}
}

两个队列实现一个栈

import java.util.ArrayDeque;
import java.util.Queue;public class Demo08 {Queue<Integer> queue1 = new ArrayDeque<>();Queue<Integer> queue2 = new ArrayDeque<>();public void push(int node) {//两个栈都为空时，优先考虑queue1if (queue1.isEmpty()&&queue2.isEmpty()) {queue1.add(node);return;}//如果queue1为空，queue2有元素，直接放入queue2if (queue1.isEmpty()) {queue2.add(node);return;}if (queue2.isEmpty()) {queue1.add(node);return;}}public int pop() {//两个栈都为空时，没有元素可以弹出if (queue1.isEmpty()&&queue2.isEmpty()) {try {throw new Exception("stack is empty");} catch (Exception e) {}}//如果queue1为空，queue2有元素， 将queue2的元素依次放入queue1中，直到最后一个元素，我们弹出。if (queue1.isEmpty()) {while (queue2.size()>1) {queue1.add(queue2.poll());}return queue2.poll();}if (queue2.isEmpty()) {while (queue1.size()>1) {queue2.add(queue1.poll());}return queue1.poll();}return (Integer) null;}public static void main(String[] args) {Demo08 demo08 = new Demo08();demo08.push(1);demo08.push(2);demo08.push(3);demo08.push(4);System.out.println(demo08.pop());System.out.println(demo08.pop());demo08.push(5);System.out.println(demo08.pop());System.out.println(demo08.pop());System.out.println(demo08.pop());}
}