1.3.39环形缓冲区。环形缓冲区，又称环形队列，是一种定长为N的先进先出的数据结构。它在进程间的异步数据传输或记录日志文件时十分有用。当缓冲区为空时，消费者会在数据存入缓冲区前等待;当缓冲区满时，生产者会等待将数据存入缓冲区。为RingBuffer设计一份API并用(回环)数组将其实现。

答：

import java.util.Iterator;

public class RingBuffer<Item> implements Iterable<Item>

{

   private Item[] a;

   private int N;

   private int left;

   private int right;

 

    public RingBuffer(int arraryLength)

    {

        a=(Item[]) new Object[arraryLength];

        left=0;

        right=0;

        N=0;

    }

  

    public boolean isEmpty()

    {return N==0;}

   

    public boolean isFull()

    {return N==a.length;}

  

    public int size()

    {return N;}

  

  

    public void enqueue(Item item)

    {

       if(isFull()) return;

        right++;

        if(right==a.length) right=0;

        a[right]=item;

        if(isEmpty()) left=right;

        N++;

    }

  

    public Item dequeue()

    {

        Item item;

       if(isEmpty())

       {

           item=null;

       }

       else if(size()==1)

       {

           item=a[left];

           N--;

       }

       else

       {

           item=a[left];

           left++;

           if(left==a.length) left=0;

           N--;

       }

        return item;

    }

      

    public Iterator<Item> iterator()  {return new ListIterator();}

  

    private class ListIterator implements Iterator<Item>

    {

        private int current=left;

        public boolean hasNext(){return current!=right+1;}

        public void remove(){}

        public Item next()

        {

            Item item=a[current];

            current++;

            if(current==a.length) current=0;

            return item;

        }//end next

      }//end class ListIterator

}//end class