用java中的HashMap实现队列

 

1. import java.util.*;
3. public class VarCostRateQueue {
4.     private final static int size=20;
5.     private static HashMap storage=new HashMap(size);
6.     private static String[] keySet=new String[size];
7.     private static int head=-1,trail=-1;
8.     public VarCostRateQueue(){}
9.     public static void push(String key,Object obj)throws Exception
10.     {
11.         synchronized(storage)
12.         {
13.             synchronized(keySet)
14.             {
15.                 if(storage.get(key)==null)
16.                 {
17.                     trail=(trail+1)%20;
18.                     if(trail==head)
19.                     {
20.                         storage.remove(keySet[head]);
21.                         head=(head+1)%20;
22.                         storage.put(key, obj);
23.                         keySet[trail]=key;
24.                     }else
25.                     {
26.                         storage.put(key, obj);
27.                         keySet[trail]=key;
28.                         if(head==-1)
29.                             head=0;
30.                     }
31.                 }
32.             }
33.         }
34.     }
35.     public static Object get(String key)throws Exception
36.     {
37.         return storage.get(key);
38.     }
39.     private static void clear()throws Exception
40.     {
41.         synchronized(storage)
42.         {
43.             storage.clear();
44.             head=-1;
45.             trail=-1;
46.         }
47.         
48.     }
50. }