/
ch27a.html
67 lines (41 loc) · 3.12 KB
/
ch27a.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
<!doctype html>
<html lang="en">
<head>
<meta http-equiv="x-ua-compatible" content="ie=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="Study guide for the Oracle Certified Professional, Java SE 8 Programmer Exam ">
<title>Java 8 Programmer II Study Guide: Exam 1Z0-809</title>
<link href="css/code.css" rel="stylesheet" type="text/css" />
<link href="css/style.css" rel="stylesheet" type="text/css" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.2.2/jquery.min.js"></script>
<script src="js/common-sections.js"></script>
</head>
<body>
<div class="header">
<div class="title-container">
<div class="chapter-title">
<h1><i class="chapter">Chapter TWENTY-SEVEN</i><br />
Concurrency</h1>
<p><br /></p>
<h3 style="text-align: center;"><i>Exam Objectives</i></h3>
<p style="text-align: center;"><i>Use synchronized keyword and java.util.concurrent.atomic package to control the order of thread execution.<br /></i><i>Use java.util.concurrent collections and classes including CyclicBarrier and CopyOnWriteArrayList.</i></p>
</div>
</div>
</div>
<div class="container">
<div class="column">
<h2>Answers</h2>
<p><b>1. The correct answer is B.</b><br /> Option A is false. <code>ConcurrentSkipListMap</code> is the only implementation of <code>ConcurrentNavigableMap</code>.<br /> Option B is true. Whenever there's a modification to a <code>CopyOnWriteArrayList</code> list, it creates a new copy of the underlying array.<br /> Option C is false. A <code>static</code> method can only use static variables, so it can only acquire the lock of static variables or the lock of variables defined inside the method.<br /> Option D is false. A constructor cannot be synchronized because only one thread has access to the object when it is being created.</p>
<p><br /></p>
<p><b>2. The correct answer is D.</b><br /> Only option D performs the operation atomically. The other options perform the operation in two steps, which makes it vulnerable to race conditions.</p>
<p><br /></p>
<p><b>3. The correct answer is D.</b><br />
<code>offerLast()</code> inserts <code>10</code> to the <code>Deque</code> (the timeout value doesn't apply here because the <code>Deque</code> is not full). Then, <code>pollLast()</code> removes that value and returns it. At this point, the deque is empty, so <code>pollFirst()</code> will wait for 5 seconds to see if another thread inserts another value. Since this didn't happen, <code>null</code> is finally returned.</p>
<p><br /></p>
<p><b>4. The correct answer is C.</b><br /> The <code>await()</code> method throws an <code>InterruptedException</code> if the current thread was interrupted while waiting and a <code>BrokenBarrierException</code> if another thread was interrupted or timed out.</p>
<p><br /></p>
</div>
</div>
<footer></footer>
</body>
</html>