leetcode-java-225. Implement Stack using Queues

class MyStack {    // Push element x onto stack.    List<Integer> queue1 = new LinkedList<Integer>();    List<Integer> queue2 = new LinkedList<Integer>();    public void push(int x) {        if(!queue1.isEmpty()) {            queue1.add(x);        } else {            queue2.add(x);        }    }    // Removes the element on top of the stack.    public void pop() {        // 两个队列中至少有一个为空，将queue1设置非空        if(queue1.isEmpty()) {            List<Integer> tmp = queue2;            queue2 = queue1;            queue1 = tmp;        }        while(queue1.size() > 1) {            queue2.add(queue1.remove(0));        }        queue1.clear();    }    // Get the top element.    public int top() {        // 两个队列中至少有一个为空，将queue1设置非空        if(queue1.isEmpty()) {            List<Integer> tmp = queue2;            queue2 = queue1;            queue1 = tmp;        }        while(queue1.size() > 1) {            queue2.add(queue1.remove(0));        }        queue2.add(queue1.get(0));        return queue1.remove(0);    }    // Return whether the stack is empty.    public boolean empty() {        return queue1.isEmpty() && queue2.isEmpty();    }}