Algs4-1.3.39环形缓冲区

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