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<!doctype html>
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<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>
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<h1><i class="chapter">Chapter EIGHTEEN</i><br />
Parallel Streams</h1>
<p><br /></p>
<h3 style="text-align: center;"><i>Exam Objectives</i></h3>
<p style="text-align: center;"><i>Use parallel Streams including reduction, decomposition, merging processes, pipelines and performance.</i><br /></p>
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<h2>Answers</h2>
<p><b>1. The correct answer is B.</b><br /> Sums are associative operations, therefore, the <code>reduce()</code> method ensures that the stream can be processed in parallel while preserving the order of its elements.</p>
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<p><b>2. The correct answer is C.</b><br /> Option A is false. <code>Collection</code>s use the <code>parallelStream()</code> method.<br /> Option B is false. Operations that are computationally expensive, generally have a better performance using a parallel stream.<br /> Option C is true. <code>filter()</code> is considered stateless.<br /> Option D is false. Parallel streams don't always perform better than sequential streams.</p>
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<p><b>3. The correct answer is A.</b><br /> If you remember from the previous chapter, the <code>average()</code>, <code>sum()</code>, <code>max()</code>, and <code>min()</code> methods are implemented as a reduce operation with the <code>collect()</code> method, so the stream can be safely processed in parallel.</p>
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<p><b>4. The correct answer is D.</b><br /> The call of <code>sequential()</code> turns the whole stream pipeline into a sequential one. In general, we can say that the last call to <code>parallel()</code> or <code>sequential()</code> is the one that affects the whole stream pipeline.</p>
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