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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 SIXTEEN</i><br />
Stream Operations on Collections</h1>
<p><br /></p>
<h3 style="text-align: center;"><i>Exam Objectives</i></h3>
<p style="text-align: center;"><i>Develop code that uses Stream data methods and calculation methods.<br /></i><i>Use java.util.Comparator and java.lang.Comparable interfaces.<br /></i><i>Sort a collection using Stream API.</i></p>
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<h2>Answers</h2>
<p><b>1. The correct answer is A.</b><br />
<code>String::compareTo</code> is a valid method reference. Since <code>compareTo</code> sorts in natural order (<code>A</code>, <code>B</code>, <code>C</code>, etc.), <code>"Collections"</code> becomes the first element of the <code>List</code>.</p>
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<p><b>2. The correct answer is D.</b><br /> Option A is invalid. <code>Comparator</code> takes two arguments.<br /> Option B is invalid. <code>reversed()</code> is not a <code>static</code> method.<br /> Option C is invalid. <code>thenComparing</code> is not a <code>static</code> method.<br /> Option D is valid. The <code>static</code> method <code>Comparator.comparing</code> takes a lambda expression with one argument that represents a <code>Function</code> that returns the property on which a <code>Comparator</code> is created.</p>
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<p><b>3. The correct answer is C.</b><br /> The <code>max</code> method of the <code>Stream</code> interface takes a <code>Comparator</code> as an argument. It's not like the <code>max</code> method of the primitive streams that know how to calculate the maximum element.</p>
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<p><b>4. The correct answer is C.</b><br /> The <code>static</code> method <code>Comparator.comparing</code> takes a lambda expression with one argument that represents a <code>Function</code>. Taking two arguments would require a <code>BiFunction</code>.</p>
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