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ch26a.html
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<!doctype html>
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<title>Java 8 Programmer II Study Guide: Exam 1Z0-809</title>
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<h1><i class="chapter">Chapter TWENTY-SIX</i><br />
Thread Basics</h1>
<p><br /></p>
<h3 style="text-align: center;"><i>Exam Objectives</i></h3>
<p style="text-align: center;"><i>Create worker threads using Runnable, Callable and use an ExecutorService to concurrently execute tasks.<br /></i><i>Identify potential threading problems among deadlock, starvation, livelock, and race conditions.</i></p>
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<h2>Answers</h2>
<p><b>1. The correct answer is B.</b><br />
<code>submit()</code> only takes either a <code>Runnable</code> or a <code>Callable</code> instance as an argument. The method signature of the <code>Callable</code> interface doesn't take any argument and returns a value.</p>
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<p><b>2. The correct answers are C and D.</b><br /> Option A is false. The <code>submit()</code> method accepts a <code>Runnable</code> and returns a <code>Future</code> object.<br /> Option B is false. <code>Executors</code> don't implement <code>AutoCloseable</code>. They are closed by calling the <code>shutdown()</code> or <code>shutdownNow()</code> methods.<br /> Option C is true. A <code>Callable</code> task can be canceled with the <code>Future.cancel()</code> method.<br /> Option D is true. A thread pool contains worker threads, which are generic threads that can execute any <code>Runnable</code> or <code>Callable</code> task.</p>
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<p><b>3. The correct answer is A.</b><br /> The <code>get(long, TimeUnit)</code> method waits for at most the given time for the task to complete, and then retrieves its result. If there's no result yet, an exception is thrown.</p>
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<p><b>4. The correct answer is B.</b><br /> One thread locks A and is trying to acquire the lock of B. At the same another thread is doing the opposite, it locks B and is trying the acquire the lock of A, so they are permanently blocked. This is a deadlock situation.</p>
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