使用栈实现队列(2)(Java)

 class MyQueue
 {
     private Stack s1;
     private Stack s2;

     public MyQueue(int size)
     {
         this.s1 = new Stack(size);
         this.s2 = new Stack(size);
     }

     public boolean isFull()
     {
         return s1.isFull();
     }

     public boolean isEmpty()
     {
         return s1.isEmpty();
     }

     //时间复杂度: O(n)
     public void EnQueue(int k) throws Exception
     {
         if(s1.isFull())
             throw new Exception("Overflow.");
         else
         {
             while(!s1.isEmpty())
                 s2.push(s1.pop());
             s1.push(k);
             while(!s2.isEmpty())
                 s1.push(s2.pop());
         }
     }

     //时间复杂度: O(1)
     public int DeQueue() throws Exception
     {
         if(s1.isEmpty())
             throw new Exception("Underflow.");
         else
             return s1.pop();
     }
 }

 class Stack
 {
     private int top;
     private int[] a;

     public Stack(int size)
     {
         this.top = -1;
         this.a = new int[size];
     }

     public boolean isFull()
     {
         return this.top == this.a.length - 1;
     }

     public boolean isEmpty()
     {
         return this.top == -1;
     }

     public void push(int k) throws Exception
     {
         /*if(this.isFull())
             throw new Exception("Overflow.");*/
         //else
             this.a[++top] = k;
     }

     public int pop() throws Exception
     {
         /*if(this.isEmpty())
             throw new Exception("Underflow.");*/
         //else
             return this.a[top--];
     }

     public int getLength()
     {
         return this.top + 1;
     }
 }