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Functional Java

- Java BGGA Examples

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<h2>Java BGGA Examples</h2>

<p><div id="preamble">

<div class="sectionbody">

<div class="paragraph">

<p>These examples use the original (now obsolete) BGGA proposed syntax. Corresponding examples are also available in <a href="examples-java8.html">Java 8</a> and <a href="examples-java7.html">Java 7</a>.</p>

</div>

<div class="paragraph">

<p>The BGGA closure prototype is required to compile these examples, which can be downloaded from <a href="http://javac.info/" class="bare">http://javac.info/</a>. Any JVM version 1.5 or higher is required to use the Functional Java library or run the compiled examples.</p>

</div>

<div class="paragraph">

<p>The example list is:</p>

</div>

<div class="ulist">

<ul>

<li> <p><a href="#arrayExists">Array exists</a></p> </li>

<li> <p><a href="#arrayFilter">Array filter</a></p> </li>

<li> <p><a href="#arrayFoldLeft">Array foldLeft</a></p> </li>

<li> <p><a href="#arrayForall">Array forall</a></p> </li>

<li> <p><a href="#arrayMap">Array map</a></p> </li>

<li> <p><a href="#listMap">List map</a></p> </li>

<li> <p><a href="#optionBind">Option bind</a></p> </li>

<li> <p><a href="#optionFilter">Option filter</a></p> </li>

<li> <p><a href="#optionMap">Option map</a></p> </li>

</ul>

</div>

</div>

</div>

<div class="sect1">

<h2 id="arrayExists">Array Exists</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Checks for the existence of a String that has all lower case characters. In this case it is true (since, the case of "what"), but without this specific case, it is false. This example uses List.forall to test the characters of the String.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Array;

import static fj.data.Array.array;

import static fj.data.List.fromString;

import static java.lang.Character.isLowerCase;

public final class Array_exists {

public static void main(final String[] args) {

final Array&lt;String&gt; a = array("Hello", "There", "what", "DAY", "iS", "iT");

final boolean b = a.exists({String s =&gt; fromString(s).forall({char c =&gt; isLowerCase(c)})});

System.out.println(b); // true ("what" provides the only example; try removing it)

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="arrayFilter">Array Filter</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Removes elements from an array that do not meet a certain criteria. In this case, we are using an array of integers and the filter removes any odd numbers.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Array;

import static fj.data.Array.array;

import static fj.Show.arrayShow;

import static fj.Show.intShow;

public final class Array_filter {

public static void main(final String[] args) {

final Array&lt;Integer&gt; a = array(97, 44, 67, 3, 22, 90, 1, 77, 98, 1078, 6, 64, 6, 79, 42);

final Array&lt;Integer&gt; b = a.filter({int i =&gt; i % 2 == 0});

arrayShow(intShow).println(b); // {44,22,90,98,1078,6,64,6,42}

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="arrayFoldLeft">Array Fold Left</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Reduces the list applying a function per element. In this case, the fold sums the elements with a starting value of 0. Since 0 + 97 + 44 + 67 + 3 + 22 + 90 + 1 + 77 + 98 + 1078 + 6 + 64 + 6 + 79 + 42 == 1774 the result of the fold is 1774.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Array;

import static fj.data.Array.array;

public final class Array_foldLeft {

public static void main(final String[] args) {

final Array&lt;Integer&gt; a = array(97, 44, 67, 3, 22, 90, 1, 77, 98, 1078, 6, 64, 6, 79, 42);

final int b = a.&lt;Integer&gt;foldLeft({int i =&gt; {int j =&gt; i + j}}, 0);

System.out.println(b); // 1774

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="arrayForall">Array Forall</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Checks that all Strings in the array have lower case characters. In this case, the check fails because of the case of "There", however, the removal of this case produces a result of true.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Array;

import static fj.data.Array.array;

import static fj.data.List.fromString;

import static java.lang.Character.isLowerCase;

public final class Array_forall {

public static void main(final String[] args) {

final Array&lt;String&gt; a = array("hello", "There", "what", "day", "is", "it");

final boolean b = a.forall({String s =&gt; fromString(s).forall({char c =&gt; isLowerCase(c)})});

System.out.println(b); // false ("There" is a counter-example; try removing it)

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="arrayMap">Array Map</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Maps a function across the array of integers. In this case, the function adds 42 to each element of the array to produce a new array.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Array;

import static fj.data.Array.array;

import static fj.Show.arrayShow;

import static fj.Show.intShow;

public final class Array_map {

public static void main(final String[] args) {

final Array&lt;Integer&gt; a = array(1, 2, 3);

final Array&lt;Integer&gt; b = a.map({int i =&gt; i + 42});

arrayShow(intShow).println(b); // {43,44,45}

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="listMap">List Map</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Maps a function across a list of integers. This is similar to the Array map. This example adds 42 to each element of the list to produce a new list.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import static fj.data.List.list;

import fj.data.List;

import static fj.Show.intShow;

import static fj.Show.listShow;

public final class List_map {

public static void main(final String[] args) {

final List&lt;Integer&gt; a = list(1, 2, 3);

final List&lt;Integer&gt; b = a.map({int i =&gt; i + 42});

listShow(intShow).println(b); // [43,44,45]

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="optionBind">Option Bind</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Binds a function across the optional value type. The function checks if the contained value is even and if it is multiples that value by 3 and returns that new value. If the contained value is odd (or if there is no value), then no value is returned (none).</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Option;

import static fj.data.Option.none;

import static fj.data.Option.some;

import static fj.Show.intShow;

import static fj.Show.optionShow;

public final class Option_bind {

public static void main(final String[] args) {

final Option&lt;Integer&gt; o1 = some(7);

final Option&lt;Integer&gt; o2 = some(8);

final Option&lt;Integer&gt; o3 = none();

final Option&lt;Integer&gt; p1 = o1.bind({int i =&gt; i % 2 == 0 ? some(i * 3) : Option.&lt;Integer&gt;none()});

final Option&lt;Integer&gt; p2 = o2.bind({int i =&gt; i % 2 == 0 ? some(i * 3) : Option.&lt;Integer&gt;none()});

final Option&lt;Integer&gt; p3 = o3.bind({int i =&gt; i % 2 == 0 ? some(i * 3) : Option.&lt;Integer&gt;none()});

optionShow(intShow).println(p1); // None

optionShow(intShow).println(p2); // Some(24)

optionShow(intShow).println(p3); // None

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="optionFilter">Option Filter</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Removes the value from the optional value if it does not match a given predicate. In this case the condition for preservation is that the contained value is an even number.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Option;

import static fj.data.Option.none;

import static fj.data.Option.some;

import static fj.Show.intShow;

import static fj.Show.optionShow;

public final class Option_filter {

public static void main(final String[] args) {

final Option&lt;Integer&gt; o1 = some(7);

final Option&lt;Integer&gt; o2 = none();

final Option&lt;Integer&gt; o3 = some(8);

final Option&lt;Integer&gt; p1 = o1.filter({int i =&gt; i % 2 == 0});

final Option&lt;Integer&gt; p2 = o2.filter({int i =&gt; i % 2 == 0});

final Option&lt;Integer&gt; p3 = o3.filter({int i =&gt; i % 2 == 0});

optionShow(intShow).println(p1); // None

optionShow(intShow).println(p2); // None

optionShow(intShow).println(p3); // Some(8)

}

}</code></pre>

</div>

</div>

</div>

</div>

<div class="sect1">

<h2 id="optionMap">Option Map</h2>

<div class="sectionbody">

<div class="paragraph">

<p>Maps a function across the optional value type. The function adds 42 to any contained value.</p>

</div>

<div class="listingblock">

<div class="content">

<pre class="prettyprint highlight"><code class="language-java" data-lang="java">import fj.data.Option;

import static fj.data.Option.none;

import static fj.data.Option.some;

import static fj.Show.intShow;

import static fj.Show.optionShow;

public final class Option_map {

public static void main(final String[] args) {

final Option&lt;Integer&gt; o1 = some(7);

final Option&lt;Integer&gt; o2 = none();

final Option&lt;Integer&gt; p1 = o1.map({int i =&gt; i + 42});

final Option&lt;Integer&gt; p2 = o2.map({int i =&gt; i + 42});

optionShow(intShow).println(p1); // Some(49)

optionShow(intShow).println(p2); // None

}

}</code></pre>

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