用栈实现队列

代码简单，不在解释

package lesson01;

import java.util.Stack;

public class Code03_TwoStackQueue {

	Stack<Integer> stackPush;
	Stack<Integer> stackPop;

	public Code03_TwoStackQueue() {
		stackPush = new Stack<Integer>();
		stackPop = new Stack<Integer>();
	}

	public void push(int item) {
		stackPush.push(item);
	}

	public int poll() throws Exception {
		if (stackPush.isEmpty() && stackPop.isEmpty()) {
			throw new Exception("Queue is empty!");
		} else if (stackPop.isEmpty()) {
			while (!stackPush.isEmpty()) {
				stackPop.push(stackPush.pop());
			}
		}
		return stackPop.pop();

	}

	public int peek() throws Exception {
		if (stackPush.isEmpty() && stackPop.isEmpty()) {
			throw new Exception("Queue is empty!");
		} else if (stackPop.isEmpty()) {
			while (!stackPush.isEmpty()) {
				stackPop.push(stackPush.pop());
			}
		}
		return stackPop.peek();

	}

	public static void main(String[] args) throws Exception {
		Code03_TwoStackQueue queue = new Code03_TwoStackQueue();
		for (int i = 0; i < 7; i++) {
			queue.push(i);
		}

		for (int i = 0; i < 7; i++) {
			System.out.print(" " + queue.poll());
		}

	}

}