使用队列实现栈(1)(Java)

 class MyStack
 {
     private Queue q1;
     private Queue q2;

     public MyStack(int size)
     {
         this.q1 = new Queue(size);
         this.q2 = new Queue(size);
     }

     public boolean isFull()
     {
         return q1.isFull();
     }

     public boolean isEmpty()
     {
         return q1.isEmpty();
     }

     //时间复杂度: O(n)
     public void push(int k) throws Exception
     {
         if(this.isFull())
             throw new Exception("Overflow.");
         else
         {
             while(!this.q1.isEmpty())
                 this.q2.EnQueue(this.q1.DeQueue());
             this.q1.EnQueue(k);
             while(!this.q2.isEmpty())
                 this.q1.EnQueue(this.q2.DeQueue());
         }
     }

     //时间复杂度: O(1)
     public int pop() throws Exception
     {
         if(this.isEmpty())
             throw new Exception("Underflow");
         else
             return this.q1.DeQueue();
     }
 }

 class Queue
 {
     private int front;
     private int rear;
     private int[] a;

     public Queue(int size)
     {
         this.front = this.rear = 0;
         this.a = new int[size];
     }

     public boolean isFull()
     {
         return (this.rear + 1) % this.a.length == this.front;
     }

     public boolean isEmpty()
     {
         return this.rear == this.front;
     }

     public void EnQueue(int k) throws Exception
     {
         //该判断是冗余的
         /*if(this.isFull())
          *
             throw new Exception("Overflow.");*/
         //else
         {
             this.a[this.rear] = k;
             this.rear = (this.rear + 1) % this.a.length;
         }

     }

     public int DeQueue() throws Exception
     {
         //该判断是冗余的
         /*if(this.isEmpty())
             throw new Exception("Underflow.");*/
         //else
         {
             int key = this.a[front];
             this.front = (this.front + 1) % this.a.length;
             return key;
         }
     }

     public int getLength()
     {
         return (this.rear - this.front + this.a.length) % this.a.length;
     }
 }