利用栈实现队列

public class MyQueue {

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

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

    public void push(int pushInt) {
        stackPush.push(pushInt);
        dump();
    }

    public int poll() {
        if (stackPop.empty() && stackPush.empty()) {
            throw new RuntimeException("Queue is empty!");
        }
        dump();
        return stackPop.pop();
    }

    public int peek() {
        if (stackPop.empty() && stackPush.empty()) {
            throw new RuntimeException("Queue is empty!");
        }
        dump();
        return stackPop.peek();
    }

    public void dump() {
        if (!stackPop.isEmpty()) {
            return;
        }
        while (!stackPush.isEmpty()) {
            stackPop.push(stackPush.pop());
        }
    }
}