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ch11a.html
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ch11a.html
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<!doctype html>
<html lang="en">
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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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<div class="header">
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<div class="chapter-title">
<h1><i class="chapter">Chapter ELEVEN</i><br />
Method References</h1>
<p><br /></p>
<h3 style="text-align: center;"><i>Exam Objectives</i></h3>
<p style="text-align: center;"><i>Use method references with Streams.</i><br /></p>
</div>
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<div class="column">
<h2>Answers</h2>
<p><b>1. The correct answer is B.</b><br /></p>
<p><code class="java hljs">Runnable r = Question_11_1::print;</code></p>
<p>It's equivalent to:<br /></p>
<p><code class="java hljs">Runnable r = () -> Question_11_1.print();</code></p>
<p>And equivalent to:<br /></p>
<p><code class="java hljs">Runnable r = <span class="hljs-keyword">new</span> Runnable() {<br />
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span><span class="hljs-params">()</span></span> {<br />
Question_11_1.print();<br />
}<br />
}</code></p>
<p>The <code>print()</code> method returns another <code>Runnable</code> instance, but as this is not saved or executed, nothing is done.</p>
<p><br /></p>
<p><b>2. The correct answer is A.</b><br /></p>
<p><code class="java hljs">Consumer c = Question_11_2::print;</code></p>
<p>It's equivalent to:<br /></p>
<p><code class="java hljs">Consumer c = (Question_11_2 q) -> q.print();</code></p>
<p>And equivalent to:<br /></p>
<p><code class="java hljs">Consumer c = <span class="hljs-keyword">new</span> Consumer() {<br />
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">accept</span><span class="hljs-params">(Question_11_2 q)</span></span> {<br />
q.print();<br />
}<br />
}</code></p>
<p>That when executed, it just prints <code>"Hi"</code>.</p>
<p><br /></p>
<p><b>3. The correct answers are A and C.</b><br /> Option A is true. You can have a method reference of a constructor.<br /> Option B is false. Method references only replace one-method lambda expressions.<br /> Option C is true. When using method references, you don't have to specify the arguments the method receives.<br /> Option D is false. The <code>::</code> operator is just used in method references.</p>
<p><br /></p>
<p><b>4. The correct answer is D.</b><br /> Option A and B are not valid method references.<br /> Option C would be right if the method <code>drive(int)</code> were <code>static</code>, but because it's an instance method, option D is the right one.</p>
<p><br /></p>
<p><b>5. The correct answer is B.</b><br /></p>
<p><code class="java hljs">Runnable r = Question_11_5::<span class="hljs-keyword">new</span>;</code></p>
<p>It's equivalent to:<br /></p>
<p><code class="java hljs">Runnable r = () -> <span class="hljs-keyword">new</span> Question_11_5();</code></p>
<p>And equivalent to:<br /></p>
<p><code class="java hljs">Runnable r = <span class="hljs-keyword">new</span> Runnable() {<br />
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span><span class="hljs-params">()</span></span> {<br />
<span class="hljs-keyword">new</span> Question_11_5();<br />
}<br />
}</code></p>
<p>However, <code>r.run()</code> is never executed, so nothing is printed.</p>
<p><br /></p>
<p><b>6. The correct answer is D.</b><br /> Compilation fails because<br /></p>
<p><code class="java hljs">BiFunction<String, String, Test> f = Test::<span class="hljs-keyword">new</span>;</code></p>
<p>It's equivalent to:<br /></p>
<p><code class="java hljs">BiFunction<String, String, Test> f =<br />
(String s1, String s2) -> <span class="hljs-keyword">new</span> Test(s1, s2);</code></p>
<p>And class <code>Test</code> only has constructors that take zero and one arguments.</p>
<p><br /></p>
<p><b>7. The correct answers are A and D.</b><br /> Option A is correct because the private constructor can be used inside the <code>main</code> method.<br /> Option B is wrong because with an <code>UnaryOperator</code>, a parameter of type <code>Question_11_7</code> is expected.<br /> Option C is wrong because with a <code>Consumer</code> a parameter of type <code>Question_11_7</code> is expected, and nothing is returned.<br /> Option D is correct because a <code>Supplier</code> returns an instance of <code>Question_11_7</code> by calling the <code>static</code> method <code>create()</code>.</p>
<p><b><br /></b></p>
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