Java-----实现一个简单的栈结构

这是一道很常见的面试题  不用Java的内置的Array、List、Set去完成

 

public class Stack<V> {

   //模拟队列
    private class Queue {
        public V v;
        public Queue next;
    }

    //栈顶
    private Queue sp;  
    //长度
    private long length;

   //入栈
    public void push(V v) {
        Queue q = new Queue();
        q.v = v;
        if (sp == null) {
            sp = q;
        }else {
            q.next = sp;
            sp = q;
        }
        length ++;
    }

   //出栈
    public V poll() throws Exception {
        if (sp == null) {
            throw new Exception("空栈");
        }else {
            Queue q= sp;
            sp = q.next;
            length--;
            return r.v;
        }
    }

    public long getLength() {
        return length;
    }
}