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| </div><div id='content' class='page-1'><div class='row'><div class='row-fluid'><div class='col-lg-3'><ul class='nav-sidebar'><li><a href='./'>Blog index</a></li><li class='active'><a href='#doc'>Groovy Processing Nulls In Lists</a></li><li><a href='#_libraries_covered' class='anchor-link'>Libraries covered</a></li><li><a href='#_mutating_a_list_to_remove_its_nulls' class='anchor-link'>Mutating a list to remove its nulls</a></li><li><a href='#_producing_a_new_list_without_nulls' class='anchor-link'>Producing a new list without nulls</a></li><li><a href='#_other_null_related_functionality' class='anchor-link'>Other null related functionality</a></li><li><a href='#_further_information' class='anchor-link'>Further Information</a></li></ul><br/><ul class='nav-sidebar'><li style='padding: 0.35em 0.625em; background-color: #eee'><span>Related posts</span></li><li><a href='./groovy-list-processing-cheat-sheet'>Groovy List Processing Cheat Sheet</a></li><li><a href='./zipping-collections-with-groovy'>Zipping Collections with Groovy</a></li><li><a href='./wordle-checker'>Checking Wordle with Groovy</a></li><li><a href='./deep-learning-and-eclipse-collections'>Deep Learning and Eclipse Collections</a></li><li><a href='./deck-of-cards-with-groovy'>Deck of cards with Groovy, JDK collections and Eclipse Collections</a></li><li><a href='./lego-bricks-with-groovy'>Lego Bricks with Groovy</a></li><li><a href='./groovy-haiku-processing'>Groovy Haiku processing</a></li><li><a href='./fruity-eclipse-collections'>Fruity Eclipse Collections</a></li></ul></div><div class='col-lg-8 col-lg-pull-0'><a name='doc'></a><h1>Groovy Processing Nulls In Lists</h1><p><span>Author: <i>Paul King</i></span><br/><span>Published: 2023-02-06 12:00AM</span></p><hr/><div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>This <a href="https://www.programmergirl.com/java-remove-nulls-from-list/">article</a> by <a href="https://www.programmergirl.com/about-me/">Shubhra Srivastava</a> |
| looks at processing lists containing nulls in Java. Let’s look at doing the same in Groovy. |
| Shubhra’s article covered both mutating the list in place and producing a new list, |
| so we’ll cover both cases.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_libraries_covered">Libraries covered</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Shubhra’s article examined <em>"out-of-the-box"</em> Java and some other collections libraries. |
| We’ll look at using those same libraries with Groovy, but we’ll cover Eclipse Collections too.</p> |
| </div> |
| <div class="paragraph"> |
| <p>In summary, we’ll cover:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><em>"Out-of-the-box"</em> <a href="https://groovy-lang.org/">Groovy</a> (which includes JDK functionality)</p> |
| </li> |
| <li> |
| <p><a href="https://github.com/google/guava/wiki">Guava</a> which provides a number of extensions to the JDK collections ecosystem. In particular, it has immutable collections, new collection types like multisets and bidirectional maps and various powerful extensions and utilities.</p> |
| </li> |
| <li> |
| <p><a href="https://commons.apache.org/proper/commons-collections/">Apache Commons Collections</a> which extends upon the JDK collections framework adding some new types like bidirectional maps and bags |
| as well as providing many comparator and iterator implementations. The library was designed to fill |
| gaps in the JDK offerings and while some of those gaps in the JDK have now been filled by the JDK |
| itself, Commons Collections still contains much useful functionality.</p> |
| </li> |
| <li> |
| <p><a href="https://www.eclipse.org/collections/">Eclipse Collections</a> which comes with many container types including |
| immutable collections, primitive collections, bimaps, multimaps and bags as well as numerous utility |
| methods. It focuses on reduced memory footprint and efficient containers. It might be particularly |
| of interest if you need primitive collections, immutable collections or some more exotic collection |
| types like bag or bidirectional maps.</p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_mutating_a_list_to_remove_its_nulls">Mutating a list to remove its nulls</h2> |
| <div class="sectionbody"> |
| <div class="sect2"> |
| <h3 id="_groovy">Groovy</h3> |
| <div class="paragraph"> |
| <p>With Groovy, we can follow Java’s lead and use <code>removeIf</code> or use Groovy’s <code>removeAll</code>. |
| In either case, we can use a method reference, closure syntax or lambda syntax |
| to capture the desired non-null constraint.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var list = ['A', null, 'B', null, 'C'] |
| list.removeIf(Objects::isNull) |
| assert list.size() == 3</code></pre> |
| </div> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var list = ['A', null, 'B', null, 'C'] |
| list.removeAll(s -> s == null) |
| assert list.size() == 3</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_guava">Guava</h3> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var list = ['A', null, 'B', null, 'C'] |
| Iterables.removeIf(list, Predicates.isNull()) |
| assert list.size() == 3</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_apache_commons_collections">Apache Commons Collections</h3> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var list = ['A', null, 'B', null, 'C'] |
| CollectionUtils.filter(list, PredicateUtils.notNullPredicate()) |
| assert list.size() == 3</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_eclipse_collections">Eclipse Collections</h3> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">var list = Lists.mutable.of('A', null, 'B', null, 'C') |
| list.withoutAll([null]) |
| assert list.size() == 3</code></pre> |
| </div> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_producing_a_new_list_without_nulls">Producing a new list without nulls</h2> |
| <div class="sectionbody"> |
| <div class="sect2"> |
| <h3 id="_groovy_2">Groovy</h3> |
| <div class="paragraph"> |
| <p>We can use Java streams as per the original article or avoid streams and use Groovy’s <code>findAll</code> method:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert ['A', null, 'B'].stream().filter(Objects::nonNull).toList().size() == 2 |
| assert ['A', null, 'B'].findAll(Objects::nonNull).size() == 2</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>In this case, we can also use <code>findAll</code> and <code>grep</code> no-arg shortcuts. |
| These shortcuts follow <a href="https://groovy-lang.org/semantics.html#the-groovy-truth">Groovy truth</a> |
| which will remove nulls but also empty Strings and zeros. This may or may not be what we want.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert ['A', null, 'B'].findAll().size() == 2 |
| assert ['A', null, 'B'].grep().size() == 2 |
| |
| assert ['A', null, 'B', '', 0].findAll().size() == 2 |
| assert ['A', null, 'B', '', 0].grep().size() == 2</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Groovy also has the <code>findResults</code> method which specifically looks |
| for non-null results rather than applying Groovy truth:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert ['A', null, 'B'].findResults{ it }.size() == 2 |
| assert ['A', null, 'B'].findResults().size() == 2 // <b class="conum">(1)</b> |
| assert ['A', null, 'B', '', 0].findResults().size() == 4 // <b class="conum">(1)</b></code></pre> |
| </div> |
| </div> |
| <div class="colist arabic"> |
| <ol> |
| <li> |
| <p>The no-arg shortcut variants are available from Groovy 4.0.9 onwards.</p> |
| </li> |
| </ol> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_guava_2">Guava</h3> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert Iterables.filter(['A', null, 'B'], Predicates.notNull()).size() == 2</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_apache_commons_collections_2">Apache Commons Collections</h3> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert CollectionUtils.select(['A', null, 'B'], PredicateUtils.notNullPredicate()).size() == 2</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_eclipse_collections_2">Eclipse Collections</h3> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="prettyprint highlight"><code data-lang="groovy">assert Lists.mutable.of('A', null, 'B').select(Predicates.notNull()).size() == 2</code></pre> |
| </div> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_other_null_related_functionality">Other null related functionality</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Before concluding, we should mention some other Groovy functionality related to null. |
| Although not related to list processing, Groovy’s <code>@NullCheck</code> AST transform is useful |
| to automatically add null checking into your own classes, methods, and constructors. For further details, |
| see the <a href="https://docs.groovy-lang.org/latest/html/documentation/#xform-NullCheck">documentation</a>.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_further_information">Further Information</h2> |
| <div class="sectionbody"> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Java – Remove all nulls from a List (<a href="https://www.programmergirl.com/java-remove-nulls-from-list/">original</a> and <a href="https://www.javacodegeeks.com/2019/03/java-remove-nulls-from-list.html">javacodegeeks</a>)</p> |
| </li> |
| <li> |
| <p>Eclipse Collections (<a href="https://www.eclipse.org/collections/">website</a> and <a href="https://github.com/eclipse/eclipse-collections">github site</a>)</p> |
| </li> |
| <li> |
| <p>Guava (<a href="https://github.com/google/guava/wiki">user guide</a>)</p> |
| </li> |
| <li> |
| <p>Apache Commons Collections (<a href="https://commons.apache.org/proper/commons-collections/">website</a>)</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Have fun processing nulls with Groovy!</p> |
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