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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 FIFTEEN</i><br />
Data Search</h1>
<p><br /></p>
<h3 style="text-align: center;"><i>Exam Objectives</i></h3>
<p style="text-align: center;"><i>Search for data by using search methods of the Stream classes including findFirst, findAny, anyMatch, allMatch, noneMatch.</i><br /></p>
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<h2>Finding and Matching</h2>
<p>Searching is a common operation when you have a set of data.</p>
<p>The Stream API has two types of operation for searching.</p>
<p>Methods starting with <i>Find</i>:</p>
<p><code class="java hljs"><span class="hljs-function">Optional<T> <span class="hljs-title">findAny</span><span class="hljs-params">()</span><br />
Optional<T> <span class="hljs-title">findFirst</span><span class="hljs-params">()</span></span></code></p>
<p>That search for an element in a stream. Since there's a possibility that an element couldn't be found (if the stream is empty, for example), the return type of this methods is an <code><b>Optional</b></code>.</p>
<p>And method ending with <i>Match</i>:</p>
<p><code class="java hljs"><span class="hljs-function"><span class="hljs-keyword">boolean</span> <span class="hljs-title">allMatch</span><span class="hljs-params">(Predicate<? <span class="hljs-keyword">super</span> T> predicate)</span><br />
<span class="hljs-keyword">boolean</span> <span class="hljs-title">anyMatch</span><span class="hljs-params">(Predicate<? <span class="hljs-keyword">super</span> T> predicate)</span><br />
<span class="hljs-keyword">boolean</span> <span class="hljs-title">noneMatch</span><span class="hljs-params">(Predicate<? <span class="hljs-keyword">super</span> T> predicate)</span></span></code></p>
<p>That indicate if a certain element matches the given predicate, that's why they return a <code><b>boolean</b></code>.</p>
<p>Since all these methods return a type different than a stream, they are considered <b>TERMINAL</b> operations.</p>
<h2>findAny() and findFirst()</h2>
<p><code>findAny()</code> and <code>findFirst()</code> practically do the same, they return the first element they find in a stream:</p>
<p><code class="java hljs">IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
stream.findFirst()<br />
.ifPresent(System.out::println); <span class="hljs-comment">// 1</span><br />
<br />
IntStream stream2 = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
stream2.findAny()<br />
.ifPresent(System.out::println); <span class="hljs-comment">// 1</span></code></p>
<p>If the stream is empty, they return an empty <code>Optional</code>:</p>
<p><code class="java hljs">Stream<String> stream = Stream.empty();<br />
System.out.println(<br />
stream.findAny().isPresent()<br />
); <span class="hljs-comment">// false</span></code></p>
<p>Of course, you can combine these methods with other stream operations:</p>
<p><code class="java hljs">IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
stream<br />
.filter(i -> i > <span class="hljs-number">4</span>)<br />
.findFirst()<br />
.ifPresent(System.out::println); <span class="hljs-comment">// 5</span></code></p>
<p>When to use <code>findAny()</code> and when to use <code>findFirst()</code>?</p>
<p>When working with parallel streams, it's harder to find the first element. In this case, it's better to use <code>findAny()</code> if you don't really mind which element is returned.</p>
<h2>anyMatch(), allMatch(), and noneMatch()</h2>
<p><code>anyMatch()</code> returns true if any of the elements in a stream matches the given predicate:</p>
<p><code class="java hljs">IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
System.out.println(<br />
stream.anyMatch(i -> i%<span class="hljs-number">3</span> == <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// true</span></code></p>
<p>If the stream is empty or if there's no matching element, this method returns <code>false</code>:</p>
<p><code class="java hljs">IntStream stream = IntStream.empty();<br />
System.out.println(<br />
stream.anyMatch(i -> i%<span class="hljs-number">3</span> == <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// false</span><br />
<br />
IntStream stream2 = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
System.out.println(<br />
stream2.anyMatch(i -> i%<span class="hljs-number">10</span> == <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// false</span></code></p>
<p><code>allMatch()</code> returns true only if <b>ALL</b> elements in the stream match the given predicate:</p>
<p><code class="java hljs">IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
System.out.println(<br />
stream.allMatch(i -> i > <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// true</span><br />
<br />
IntStream stream2 = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
System.out.println(<br />
stream2.allMatch(i -> i%<span class="hljs-number">3</span> == <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// false</span></code></p>
<p>If the stream is empty, this method returns <b>TRUE</b> without evaluating the predicate:</p>
<p><code class="java hljs">IntStream stream = IntStream.empty();<br />
System.out.println(<br />
stream.allMatch(i -> i%<span class="hljs-number">3</span> == <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// true</span></code></p>
<p><code>noneMatch()</code> is the opposite of <code>allMatch()</code>, it returns true if <b>NONE</b> of the elements in the stream match the given predicate:</p>
<p><code class="java hljs">IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
System.out.println(<br />
stream.noneMatch(i -> i > <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// false</span><br />
<br />
IntStream stream2 = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
System.out.println(<br />
stream2.noneMatch(i -> i%<span class="hljs-number">3</span> == <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// false</span><br />
<br />
IntStream stream3 = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
System.out.println(<br />
stream3.noneMatch(i -> i > <span class="hljs-number">10</span>)<br />
); <span class="hljs-comment">// true</span></code></p>
<p>If the stream is empty, this method returns also <b>TRUE</b> without evaluating the predicate:</p>
<p><code class="java hljs">IntStream stream = IntStream.empty();<br />
System.out.println(<br />
stream.noneMatch(i -> i%<span class="hljs-number">3</span> == <span class="hljs-number">0</span>)<br />
); <span class="hljs-comment">// true</span></code></p>
<h2>Short-circuiting</h2>
<p>All of these operations use something similar to the short-circuiting of <code>&&</code> and <code>||</code> operators.</p>
<p>Short-circuiting means that the evaluation stops once a result is found.</p>
<p>In the case of the <i>find*</i> operations, it's obvious that they stop at the first found element.</p>
<p>But in the case of the <i>*Match</i> operations, think about it, why would you evaluate all the elements of a stream when by evaluating the third element (for example) you can know if all or none (for example) of the elements will match?</p>
<p>Consider this code:</p>
<p><code class="java hljs">IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
<span class="hljs-keyword">boolean</span> b = stream<br />
.filter(i -> {<br />
System.out.println(<span class="hljs-string">"Filter:"</span> + i);<br />
<span class="hljs-keyword"> return</span> i % <span class="hljs-number">2</span> == <span class="hljs-number">0</span>; })<br />
.allMatch(i -> {<br />
System.out.println(<span class="hljs-string">"AllMatch:"</span> + i);<br />
<span class="hljs-keyword"> return</span> i < <span class="hljs-number">3</span>;<br />
});<br />
System.out.println(b);</code></p>
<p>What would you think the output will be?</p>
<p>The output:</p>
<p><code class="java hljs">Filter:<span class="hljs-number">1</span><br />
Filter:<span class="hljs-number">2</span><br />
AllMatch:<span class="hljs-number">2</span><br />
Filter:<span class="hljs-number">3</span><br />
Filter:<span class="hljs-number">4</span><br />
AllMatch:<span class="hljs-number">4</span><br />
<span class="hljs-keyword">false</span></code></p>
<p>As you can see, first of all, operations on a stream are not evaluated sequentially (in this case, first filter all the elements and then evaluate if all elements match the predicate of <code>allMatch()</code>).</p>
<p>Second, we can see that as soon as an element passes the filter predicate (like <code>2</code>) the predicate of <code>allMatch()</code> is evaluated.</p>
<p>Finally, we can see short-circuiting in action. As soon as the predicate of <code>allMatch()</code> finds an element that doesn't evaluate to true (like <code>4</code>), the two stream operations are canceled, no further elements are processed and the result is returned.</p>
<p>Just remember:</p>
<ul>
<li>With some operations, the whole stream doesn't need to be processed.</li>
<li>Stream operations are not performed sequentially.</li>
</ul>
<h2>Key Points</h2>
<ul>
<li>The Stream API has two types of operation for searching. Methods starting with <i>Find</i>: <code class="java hljs"><span class="hljs-function">Optional<T> <span class="hljs-title">findAny</span><span class="hljs-params">()</span><br />
Optional<T> <span class="hljs-title">findFirst</span><span class="hljs-params">()</span></span></code></li>
<li>And method ending with <i>Match</i>:</li>
<li style="list-style: none; display: inline"><code class="java hljs"><span class="hljs-function"><span class="hljs-keyword">boolean</span> <span class="hljs-title">allMatch</span><span class="hljs-params">(Predicate<? <span class="hljs-keyword">super</span> T> predicate)</span><br />
<span class="hljs-keyword">boolean</span> <span class="hljs-title">anyMatch</span><span class="hljs-params">(Predicate<? <span class="hljs-keyword">super</span> T> predicate)</span><br />
<span class="hljs-keyword">boolean</span> <span class="hljs-title">noneMatch</span><span class="hljs-params">(Predicate<? <span class="hljs-keyword">super</span> T> predicate)</span></span></code></li>
<li>Both types are considered <b>TERMINAL</b> operations.</li>
<li><code>findAny()</code> and <code>findFirst()</code> practically do the same, they return the first element they find in a stream. If the stream is empty, they return an empty <code>Optional</code>.</li>
<li>When working with parallel streams, it's harder to find the first element, so in this case, it's better to use <code>findAny()</code> if you don't really mind which element is returned.</li>
<li><code>anyMatch()</code> returns true if any of the elements in a stream matches the given predicate. If the stream is empty or if there's no matching element, it returns <code>false</code>.</li>
<li><code>allMatch()</code> returns true only if <b>ALL</b> elements in the stream match the given predicate.</li>
<li><code>noneMatch()</code> returns true if <b>NONE</b> of the elements in the stream match the given predicate.</li>
<li>Both <code>allMatch()</code> and <code>noneMatch()</code> return <code>true</code> if the stream is empty.</li>
<li>All of these operations are short-circuiting, meaning that the evaluation stops once a result is found.</li>
</ul>
<h2>Self Test</h2>
<p>1. Given:</p>
<p><code class="java hljs"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Question_15_1</span></span> {<br />
<span class="hljs-function"><span class="hljs-keyword"> public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">main</span><span class="hljs-params">(String[] args)</span></span> {<br />
Stream<Integer> s = Stream.of(<span class="hljs-number">100</span>, <span class="hljs-number">45</span>, <span class="hljs-number">98</span>, <span class="hljs-number">33</span>);<br />
s.anyMatch(i -> i > <span class="hljs-number">50</span>)<br />
.findAny()<br />
.ifPresent(System.out::println);<br />
}<br />
}</code></p>
<p>What is the result?<br /> A. <code>100</code><br /> B. <code>98</code><br /> C. Nothing is printed<br /> D. Compilation fails</p>
<p>2. Which of the following methods of the Stream interface returns an <code>Optional</code> type?<br /> A. <code>filter()</code><br /> B. <code>findMatch()</code><br /> C. <code>findAny()</code><br /> D. <code>anyMatch()</code></p>
<p>3. Given:</p>
<p><code class="java hljs"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Question_15_3</span></span> {<br />
<span class="hljs-function"><span class="hljs-keyword"> public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">main</span><span class="hljs-params">(String[] args)</span></span> {<br />
IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
stream.allMatch(i -> {<br />
System.out.print(i);<br />
<span class="hljs-keyword"> return</span> i % <span class="hljs-number">3</span> == <span class="hljs-number">0</span>;<br />
});<br />
}<br />
}</code></p>
<p>What is the result?<br /> A. <code>1234567</code><br /> B. <code>36</code><br /> C. <code>1</code><br /> D. Compilation fails</p>
<p>4. Given:</p>
<p><code class="java hljs"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Question_15_4</span></span> {<br />
<span class="hljs-function"><span class="hljs-keyword"> public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">main</span><span class="hljs-params">(String[] args)</span></span> {<br />
IntStream stream = IntStream.of(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>);<br />
stream.filter(i -> {<br />
<span class="hljs-keyword"> return</span> i > <span class="hljs-number">3</span>;<br />
}).anyMatch(i -> {<br />
System.out.print(i);<br />
<span class="hljs-keyword"> return</span> i % <span class="hljs-number">2</span> == <span class="hljs-number">1</span>;<br />
});<br />
}<br />
}</code></p>
<p>What is the result?<br /> A. <code>45</code><br /> B. <code>5</code><br /> C. <code>4567</code><br /> D. Compilation fails</p>
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