因此，我正在研究构建一个简单的对象缓存，该缓存在给定时间后会使对象过期。 显而易见的机制是使用Java并发包中的DelayedQueue类。 但我想知道是否有可能在将对象添加到队列后更新延迟。 看一下Delayed接口，似乎没有充分的理由不在文档中，所以我认为是时候进行实验了。

因此，首先您需要创建一个Delayed实例，这是一个非常简单的实现，通过切换标志，您基本上可以反转列表中的超时顺序。 （并添加适当的偏移量，以便按正确的顺序进行操作

static int COUNT=100;class DelayedSwap implements Delayed, Comparable<Delayed> {int index = 0;volatile boolean swap = false;long starttime;public DelayedSwap(int index, long starttime) {super();this.index = index;this.starttime = starttime;}private long getDelay() {return (swap ? starttime + (2*COUNT - index) * 100 :starttime + index * 100) - System.currentTimeMillis();}public String toString(){return index + ' swapped ' + swap + ' delay ' + getDelay();}@Overridepublic long getDelay(TimeUnit unit) {return unit.convert(getDelay(), TimeUnit.MILLISECONDS);}@Overridepublic int compareTo(Delayed delayed) {if (delayed == this)return 0;return (int)(getDelay(TimeUnit.MILLISECONDS) - delayed.getDelay(TimeUnit.MILLISECONDS));}}

因此，为了测试这一点，我创建了一个方法，该方法将创建一堆DelayedSwap对象，并在处理列表的一半过程中切换标志，从而更改到期顺序。

public static void main(String[] args) throws InterruptedException {long start = System.currentTimeMillis();final Listdelayed = new ArrayList();for (int i = 1; i < COUNT; i++) {delayed.add(new DelayedSwap(i, start));}final DelayQueue dq = new DelayQueue();dq.addAll(delayed);new Thread(new Runnable() {@Overridepublic void run() {try {TimeUnit.SECONDS.sleep(5);} catch (InterruptedException e) {}for (DelayedSwap d : delayed) {d.swap = true;}}}).start();while (!dq.isEmpty()) {System.out.println(dq.take());}}

因此，我期望的是以正确的顺序写出元素1-50，但是在交换元素之后，它们以任意顺序出现，与请求延迟时间相去甚远。

1 swapped false delay -19
2 swapped false delay -4
3 swapped false delay -4
4 swapped false delay -4
5 swapped false delay -4
6 swapped false delay -4
7 swapped false delay -4
8 swapped false delay -4
9 swapped false delay -4
10 swapped false delay -4
11 swapped false delay -4
12 swapped false delay -4
13 swapped false delay -4
14 swapped false delay -4
15 swapped false delay -4
16 swapped false delay -4
17 swapped false delay -4
18 swapped false delay -4
19 swapped false delay -4
20 swapped false delay -4
21 swapped false delay -4
22 swapped false delay -4
23 swapped false delay -4
24 swapped false delay -4
25 swapped false delay -4
26 swapped false delay -4
27 swapped false delay -4
28 swapped false delay -4
29 swapped false delay -4
30 swapped false delay -4
31 swapped false delay -4
32 swapped false delay -4
33 swapped false delay -4
34 swapped false delay -4
35 swapped false delay -4
36 swapped false delay -4
37 swapped false delay -4
38 swapped false delay -4
39 swapped false delay -5
40 swapped false delay -4
41 swapped false delay -4
42 swapped false delay -5
43 swapped false delay -4
44 swapped false delay -5
45 swapped false delay -5
46 swapped false delay -5
47 swapped false delay -5
48 swapped false delay -5
49 swapped false delay -5
50 swapped false delay -5
51 swapped true delay -6
94 swapped true delay -4306
96 swapped true delay -4506
87 swapped true delay -3606
91 swapped true delay -4006
97 swapped true delay -4606
95 swapped true delay -4406
98 swapped true delay -4706
92 swapped true delay -4106
82 swapped true delay -3106
80 swapped true delay -2906
90 swapped true delay -3906
93 swapped true delay -4206
74 swapped true delay -2306
99 swapped true delay -4806
70 swapped true delay -1906
69 swapped true delay -1806
66 swapped true delay -1506
83 swapped true delay -3206
62 swapped true delay -1107
61 swapped true delay -1007
58 swapped true delay -707
71 swapped true delay -2007
89 swapped true delay -3807
85 swapped true delay -3407
78 swapped true delay -2707
86 swapped true delay -3507
81 swapped true delay -3007
88 swapped true delay -3707
84 swapped true delay -3307
79 swapped true delay -2807
76 swapped true delay -2507
72 swapped true delay -2107
68 swapped true delay -1707
65 swapped true delay -1407
60 swapped true delay -907
57 swapped true delay -608
55 swapped true delay -408
75 swapped true delay -2408
77 swapped true delay -2608
73 swapped true delay -2208
63 swapped true delay -1208
67 swapped true delay -1608
64 swapped true delay -1308
59 swapped true delay -808
56 swapped true delay -508
54 swapped true delay -308
53 swapped true delay -208
52 swapped true delay -108
Process exited with exit code 0.

因此，诀窍是，当您知道要修改时，请先删除延迟，然后再将元素重新添加到队列中。

// Replacement swap loopfor (DelayedSwap d : delayed) {if (dq.remove(d)){d.swap = true;dq.add(d);}}

此运行产生了一组更合理的结果：

1 swapped false delay -4
2 swapped false delay -8
3 swapped false delay -14
4 swapped false delay -8
5 swapped false delay -4
6 swapped false delay -4
7 swapped false delay -4
8 swapped false delay -4
9 swapped false delay -4
10 swapped false delay -4
11 swapped false delay -4
12 swapped false delay -4
13 swapped false delay -4
14 swapped false delay -4
15 swapped false delay -4
16 swapped false delay -4
17 swapped false delay -4
18 swapped false delay -8
19 swapped false delay -4
20 swapped false delay -4
21 swapped false delay -4
22 swapped false delay -4
23 swapped false delay -4
24 swapped false delay -4
25 swapped false delay -4
26 swapped false delay -4
27 swapped false delay -4
28 swapped false delay -4
29 swapped false delay -4
30 swapped false delay -4
31 swapped false delay -4
32 swapped false delay -4
33 swapped false delay -4
34 swapped false delay -4
35 swapped false delay -4
36 swapped false delay -4
37 swapped false delay -4
38 swapped false delay -4
39 swapped false delay -5
40 swapped false delay -5
41 swapped false delay -5
42 swapped false delay -4
43 swapped false delay -4
44 swapped false delay -5
45 swapped false delay -5
46 swapped false delay -5
47 swapped false delay -5
48 swapped false delay -5
49 swapped false delay -5
50 swapped false delay -5
99 swapped true delay -5
98 swapped true delay -5
97 swapped true delay -11
96 swapped true delay -1
95 swapped true delay -5
94 swapped true delay -9
93 swapped true delay -5
92 swapped true delay -5
91 swapped true delay -5
90 swapped true delay -5
89 swapped true delay -5
88 swapped true delay -5
87 swapped true delay -5
86 swapped true delay -5
85 swapped true delay -5
84 swapped true delay -5
83 swapped true delay -5
82 swapped true delay -5
81 swapped true delay -5
80 swapped true delay -5
79 swapped true delay -5
78 swapped true delay -5
77 swapped true delay -5
76 swapped true delay -5
75 swapped true delay -5
74 swapped true delay -5
73 swapped true delay -5
72 swapped true delay -6
71 swapped true delay -5
70 swapped true delay -5
69 swapped true delay -5
68 swapped true delay -5
67 swapped true delay -5
66 swapped true delay -5
65 swapped true delay -5
64 swapped true delay -5
63 swapped true delay -6
62 swapped true delay -5
61 swapped true delay -6
60 swapped true delay -6
59 swapped true delay -6
58 swapped true delay -6
57 swapped true delay -6
56 swapped true delay -6
55 swapped true delay -6
54 swapped true delay -6
53 swapped true delay -6
52 swapped true delay -6
51 swapped true delay -6
Process exited with exit code 0.

我不认为这是对象本身的错误，因为您不会期望键更改时HashTable会命令其自身为自己，但是我对此行为感到有些惊讶。

祝您编程愉快，别忘了分享！

参考：在Gerard Davison博客博客中，我们的JCG合作伙伴 Gerard Davison在DelayQueue中更改了延迟，从而更改了顺序 。