This is an automated email from the ASF dual-hosted git repository.
git-site-role pushed a commit to branch asf-site
in repository https://gitbox.apache.org/repos/asf/groovy-dev-site.git
The following commit(s) were added to refs/heads/asf-site by this push:
new cb6ad87 2026/04/01 22:24:28: Generated dev website from
groovy-website@2533259
cb6ad87 is described below
commit cb6ad87fb7598fa03facc133774273ca265e9c27
Author: jenkins <[email protected]>
AuthorDate: Wed Apr 1 22:24:28 2026 +0000
2026/04/01 22:24:28: Generated dev website from groovy-website@2533259
---
blog/feed.atom | 13 +-
blog/groovy-null-checker.html | 700 ++++++++++++++++++++++++++++++++++++++++++
blog/index.html | 4 +-
search/search-index.json | 9 +-
4 files changed, 722 insertions(+), 4 deletions(-)
diff --git a/blog/feed.atom b/blog/feed.atom
index b06e2e3..cae691f 100644
--- a/blog/feed.atom
+++ b/blog/feed.atom
@@ -4,7 +4,18 @@
<link href="http://groovy.apache.org/blog"/>
<link href="http://groovy.apache.org/blog/feed.atom"; rel="self"/>
<id>http://groovy.apache.org/blog</id>
- <updated>2026-03-27T16:30:00Z</updated>
+ <updated>2026-04-02T10:00:00Z</updated>
+ <entry>
+ <id>http://groovy.apache.org/blog/groovy-null-checker</id>
+ <author>
+ <name>Paul King</name>
+ </author>
+ <title type="html">Compile-time null safety for Groovy&trade;</title>
+ <link href="http://groovy.apache.org/blog/groovy-null-checker"/>
+ <updated>2026-04-02T10:00:00Z</updated>
+ <published>2026-04-02T10:00:00Z</published>
+ <summary type="html">This post looks at a proposed type-checking extension
for Groovy which catches null-safety violations at compile time.</summary>
+ </entry>
<entry>
<id>http://groovy.apache.org/blog/groovy-async-await</id>
<author>
diff --git a/blog/groovy-null-checker.html b/blog/groovy-null-checker.html
new file mode 100644
index 0000000..9bfda18
--- /dev/null
+++ b/blog/groovy-null-checker.html
@@ -0,0 +1,700 @@
+<!DOCTYPE html>
+<!--[if lt IE 7]> <html class="no-js lt-ie9 lt-ie8 lt-ie7"> <![endif]-->
+<!--[if IE 7]> <html class="no-js lt-ie9 lt-ie8"> <![endif]-->
+<!--[if IE 8]> <html class="no-js lt-ie9"> <![endif]-->
+<!--[if gt IE 8]><!--> <html class="no-js"> <!--<![endif]--><head>
+ <meta charset='utf-8'/><meta http-equiv='X-UA-Compatible'
content='IE=edge'/><meta name='viewport' content='width=device-width,
initial-scale=1'/><meta name='keywords' content='null safety, type checking,
static analysis, annotations'/><meta name='description' content='This post
looks at a proposed type-checking extension for Groovy which catches
null-safety violations at compile time.'/><title>The Apache Groovy programming
language - Blogs - Compile-time null safety for Groovy&trade [...]
+</head><body>
+ <div id='fork-me'>
+ <a href='https://github.com/apache/groovy'>
+ <img style='position: fixed; top: 20px; right: -58px; border: 0;
z-index: 100; transform: rotate(45deg);'
src='../img/horizontal-github-ribbon.png'/>
+ </a>
+ </div><div id='st-container' class='st-container st-effect-9'>
+ <nav class='st-menu st-effect-9' id='menu-12'>
+ <h2 class='icon icon-lab'>Socialize</h2><ul>
+ <li>
+ <a href='https://groovy-lang.org/mailing-lists.html'
class='icon'><span class='fa fa-classic fa-regular fa-envelope'></span> Discuss
on the mailing list</a>
+ </li><li>
+ <a href='https://x.com/ApacheGroovy' class='icon'><span
class='fa fa-brands fa-x-twitter'></span> Groovy on X</a>
+ </li><li>
+ <a href='https://bsky.app/profile/groovy.apache.org'
class='icon'><span class='fa fa-brands fa-bluesky'></span> Groovy on Bluesky</a>
+ </li><li>
+ <a href='https://fosstodon.org/@ApacheGroovy'
class='icon'><span class='fa fa-brands fa-mastodon'></span> Groovy on
Mastodon</a>
+ </li><li>
+ <a
href='https://www.linkedin.com/company/106402668/admin/dashboard/'
class='icon'><span class='fa fa-brands fa-linkedin'></span> Groovy on
LinkedIn</a>
+ </li><li>
+ <a href='https://groovy-lang.org/events.html'
class='icon'><span class='fa fa-classic fa-solid fa-calendar-days'></span>
Events and conferences</a>
+ </li><li>
+ <a href='https://github.com/apache/groovy'
class='icon'><span class='fa fa-brands fa-github'></span> Source code on
GitHub</a>
+ </li><li>
+ <a href='https://groovy-lang.org/reporting-issues.html'
class='icon'><span class='fa fa-classic fa-solid fa-bug'></span> Report issues
in Jira</a>
+ </li><li>
+ <a href='http://stackoverflow.com/questions/tagged/groovy'
class='icon'><span class='fa fa-brands fa-stack-overflow'></span> Stack
Overflow questions</a>
+ </li><li>
+ <a href='http://www.groovycommunity.com/'
class='icon'><span class='fa fa-brands fa-slack'></span> Slack Community</a>
+ </li>
+ </ul>
+ </nav><div class='st-pusher'>
+ <div class='st-content'>
+ <div class='st-content-inner'>
+ <!--[if lt IE 7]>
+ <p class="browsehappy">You are using an
<strong>outdated</strong> browser. Please <a
href="http://browsehappy.com/";>upgrade your browser</a> to improve your
experience.</p>
+ <![endif]--><div><div class='navbar navbar-default
navbar-static-top' role='navigation'>
+ <div class='container'>
+ <div class='navbar-header'>
+ <button type='button'
class='navbar-toggle' data-toggle='collapse' data-target='.navbar-collapse'>
+ <span class='sr-only'></span><span
class='icon-bar'></span><span class='icon-bar'></span><span
class='icon-bar'></span>
+ </button><a class='navbar-brand'
href='../index.html'>
+ <i class='fa-classic fa-solid
fa-star'></i> Apache Groovy™
+ </a>
+ </div><div class='navbar-collapse collapse'>
+ <ul class='nav navbar-nav navbar-right'>
+ <li class=''><a
href='https://groovy-lang.org/learn.html'>Learn</a></li><li class=''><a
href='https://groovy-lang.org/documentation.html'>Documentation</a></li><li
class=''><a href='/download.html'>Download</a></li><li class=''><a
href='https://groovy-lang.org/support.html'>Support</a></li><li class=''><a
href='/'>Contribute</a></li><li class=''><a
href='https://groovy-lang.org/ecosystem.html'>Ecosystem</a></li><li class=''><a
href='/blog'>Blog pos [...]
+ <a data-effect='st-effect-9'
class='st-trigger' href='#'>Socialize</a>
+ </li><li class=''>
+ <a href='../search.html'>
+ <i class='fa-classic fa-solid
fa-magnifying-glass'></i>
+ </a>
+ </li>
+ </ul>
+ </div>
+ </div>
+ </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'>Compile-time null safety for Groovy™</a></li><li><a
href='#_introduction' class='anchor-link'>Introduction</a></li><li><a
href='#_two_levels_of_strictness' class='anchor-link'>Two levels of
strictness</a></li><li><a href='#_the_problem_the_billion_dollar_mistake_at_r
[...]
+<a href="https://github.com/paulk-asert/"; target="_blank" rel="noopener
noreferrer"><img style="border-radius:50%;height:48px;width:auto"
src="img/paulk-asert.png" alt="Paul King"></a>
+<div style="display:grid;align-items:center;margin:0.1ex;padding:0ex">
+ <div><a href="https://github.com/paulk-asert/"; target="_blank" rel="noopener
noreferrer"><span>Paul King</span></a></div>
+ <div><small><i>PMC Member</i></small></div>
+</div>
+ </div><br/><span>Published: 2026-04-02 10:00AM</span></p><hr/><div
class="sect1">
+<h2 id="_introduction">Introduction</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>A proposed enhancement, targeted for Groovy 6,
+adds compile-time null-safety analysis as a type-checking extension
+(<a href="https://issues.apache.org/jira/browse/GROOVY-11894";>GROOVY-11894</a>,
+<a href="https://github.com/apache/groovy/pull/2426";>PR #2426</a>).
+Inspired by the
+<a href="https://checkerframework.org/manual/#nullness-checker";>Checker
Framework</a>,
+<a href="https://jspecify.dev/";>JSpecify</a>, and similar tools in Kotlin and
C#,
+the proposal catches null dereferences, unsafe assignments, and
+missing null checks <em>before</em> your code ever runs.</p>
+</div>
+<div class="paragraph">
+<p>The extension plugs into Groovy’s existing <code>@TypeChecked</code>
+infrastructure — no new compiler plugins, no separate build step,
+just an annotation on the classes or methods you want checked.
+You can also use a
+<a
href="https://docs.groovy-lang.org/latest/html/documentation/#_configscript_example_static_compilation_by_default";>compiler
configuration script</a>
+to apply it across your entire codebase without needing
+to explicitly add the <code>@TypeChecked</code> annotations.</p>
+</div>
+<div class="paragraph">
+<p>This post walks through a series of bite-sized examples showing
+what the day-to-day experience would feel like.
+To make things concrete, the examples follow a running theme:
+building the backend for <em>The Groovy Shelf</em>, a fictitious online
+bookshop where customers browse, reserve, and review books.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_two_levels_of_strictness">Two levels of strictness</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>The proposal provides two checkers. Pick the level that suits
+your code:</p>
+</div>
+<table class="tableblock frame-all grid-all stretch">
+<colgroup>
+<col style="width: 25%;">
+<col style="width: 37.5%;">
+<col style="width: 37.5%;">
+</colgroup>
+<thead>
+<tr>
+<th class="tableblock halign-left valign-top">Checker</th>
+<th class="tableblock halign-left valign-top">Behaviour</th>
+<th class="tableblock halign-left valign-top">Best for</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>NullChecker</code></p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">Checks
code annotated with <code>@Nullable</code> / <code>@NonNull</code> (or
equivalents). Unannotated code passes without error.</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">Existing
projects adopting null safety incrementally.</p></td>
+</tr>
+<tr>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>StrictNullChecker</code></p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">Everything
<code>NullChecker</code> does, <em>plus</em> flow-sensitive tracking — even
unannotated <code>def x = null; x.toString()</code> is flagged.</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">New code
or modules where you want full coverage.</p></td>
+</tr>
+</tbody>
+</table>
+<div class="paragraph">
+<p>Both are enabled through <code>@TypeChecked</code>:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+class RelaxedCode { /* … */ }
+
+@TypeChecked(extensions = 'groovy.typecheckers.StrictNullChecker')
+class StrictCode { /* … */ }</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>For code bases with a mix of strictness requirements, apply the
+appropriate checker per class or per method.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_the_problem_the_billion_dollar_mistake_at_runtime">The problem: the
billion-dollar mistake at runtime</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>Tony Hoare famously called null references his
+<a
href="https://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare/";>"billion-dollar
mistake"</a>.
+In Groovy and Java, nothing stops you from writing:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code data-lang="groovy">String name = null
+println name.toUpperCase() // NullPointerException at runtime</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>The code compiles, the tests might even pass if they don’t hit that
+path, and the exception surfaces in production. The NullChecker
+proposal moves this class of error to compile time.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_example_1_looking_up_a_book_nullable_parameters">Example 1: looking
up a book — <code>@Nullable</code> parameters</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>A customer searches for a book by title. The title might come from
+a form field that wasn’t filled in, so the parameter is
<code>@Nullable</code>:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+Book findBook(@Nullable String title) {
+ if (title != null) {
+ return catalog.search(title.trim()) // ok: inside null guard
+ }
+ return Book.FEATURED
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>The checker verifies that <code>title</code> is only dereferenced inside the
+null guard. Remove the <code>if</code> and you get a compile-time error:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code>[Static type checking] - Potential
null dereference: 'title' is @Nullable</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>No runtime surprise — the mistake is caught before the code ships.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_example_2_greeting_a_customer_catching_null_arguments">Example 2:
greeting a customer — catching null arguments</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>When a customer places an order, we greet them by name.
+The name is <code>@NonNull</code> — it must always be provided:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+class OrderService {
+ static String greet(@NonNull String name) {
+ "Welcome back, $name!"
+ }
+ static void main(String[] args) {
+ greet(null) // compile error
+ }
+}</code></pre>
+</div>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code>[Static type checking] - Cannot pass
null to @NonNull parameter 'name' of 'greet'</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>The checker also catches returning <code>null</code> from a
<code>@NonNull</code> method
+and assigning <code>null</code> to a <code>@NonNull</code> field — the same
principle
+applied consistently across assignments, parameters, and returns.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_example_3_safe_access_patterns_the_checker_is_smart">Example 3: safe
access patterns — the checker is smart</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>Groovy already offers the safe-navigation operator (<code>?.</code>) for
+working with nullable values. The NullChecker understands it,
+along with several other patterns:</p>
+</div>
+<div class="paragraph">
+<p><strong>Safe navigation:</strong></p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+String displayTitle(@Nullable String title) {
+ title?.toUpperCase() // ok: safe navigation
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p><strong>Null guards:</strong></p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+String formatTitle(@Nullable String title) {
+ if (title != null) {
+ return title.toUpperCase() // ok: null guard
+ }
+ return 'Untitled'
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p><strong>Early exit:</strong></p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+String formatTitle(@Nullable String title) {
+ if (title == null) return 'Untitled' // early exit
+ title.toUpperCase() // ok: title is non-null here
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p><strong>Elvis assignment:</strong></p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions =
'groovy.typecheckers.StrictNullChecker')
+static main(args) {
+ def title = null
+ title ?= 'Untitled'
+ title.toUpperCase() // ok: elvis cleared nullable
state
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>The checker performs the same kind of narrowing that a human reader
+does: once you’ve ruled out null — whether by an <code>if</code>, an
early
+<code>return</code>, a <code>throw</code>, or an elvis assignment — the
variable is safe.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_example_4_non_null_by_default_less_annotation_noise">Example 4:
non-null by default — less annotation noise</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>Annotating every parameter and field gets tedious. Class-level
+defaults let you flip the polarity: everything is <code>@NonNull</code> unless
+you say otherwise with <code>@Nullable</code>:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code data-lang="groovy">@NonNullByDefault
+@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+class BookService {
+ String name // implicitly @NonNull
+
+ static String formatISBN(String isbn) { // isbn is implicitly @NonNull
+ "ISBN: $isbn"
+ }
+
+ static void main(String[] args) {
+ formatISBN(null) // compile error
+ }
+}</code></pre>
+</div>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code>[Static type checking] - Cannot pass
null to @NonNull parameter 'isbn' of 'formatISBN'</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>The checker recognises several class-level annotations for this:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><code>@NonNullByDefault</code> (SpotBugs, Eclipse JDT)</p>
+</li>
+<li>
+<p><code>@NullMarked</code> (<a href="https://jspecify.dev/";>JSpecify</a>)</p>
+</li>
+<li>
+<p><code>@ParametersAreNonnullByDefault</code> (JSR-305 — parameters only)</p>
+</li>
+</ul>
+</div>
+<div class="paragraph">
+<p>JSpecify’s <code>@NullUnmarked</code> can be applied to a nested
class to opt
+out of a surrounding <code>@NullMarked</code> scope.</p>
+</div>
+<div class="sect2">
+<h3 id="_integration_with_nullcheck">Integration with
<code>@NullCheck</code></h3>
+<div class="paragraph">
+<p>Groovy’s existing <code>@NullCheck</code> annotation generates
<em>runtime</em> null
+checks for method parameters. The NullChecker complements this by
+catching violations at <em>compile</em> time:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code data-lang="groovy">@NullCheck
+@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+class Greeter {
+ static String greet(String name) {
+ "Hello, $name!"
+ }
+ static void main(String[] args) {
+ greet(null) // caught at compile time
+ }
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>With <code>@NullCheck</code> on the class, the checker treats all
non-primitive
+parameters as effectively <code>@NonNull</code>. You still get the runtime
+guard as a safety net, but now you also get a compile-time error
+alerting you before the code ever executes. Parameters explicitly
+annotated <code>@Nullable</code> override this behaviour.</p>
+</div>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_example_5_lazy_initialisation_monotonicnonnull_and_lazy">Example 5:
lazy initialisation — <code>@MonotonicNonNull</code> and <code>@Lazy</code></h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>Some fields start as <code>null</code> but, once initialised, should never
be
+<code>null</code> again. The <code>@MonotonicNonNull</code> annotation
expresses this
+"write once, then non-null forever" contract:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
+class RecommendationEngine {
+ @MonotonicNonNull String cachedResult
+
+ String getRecommendation() {
+ if (cachedResult != null) {
+ return cachedResult.toUpperCase() // ok: null guard
+ }
+ cachedResult = 'Groovy in Action'
+ return cachedResult.toUpperCase() // ok: just assigned non-null
+ }
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>The checker treats <code>@MonotonicNonNull</code> fields as nullable
(requiring
+a null guard before use) but prevents re-assignment to <code>null</code> after
+initialisation:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code data-lang="groovy">void reset() {
+ cachedResult = 'something'
+ cachedResult = null // compile error
+}</code></pre>
+</div>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code>[Static type checking] - Cannot
assign null to @MonotonicNonNull variable 'cachedResult' after non-null
assignment</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>Groovy’s <code>@Lazy</code> annotation is implicitly treated as
+<code>@MonotonicNonNull</code>. Since <code>@Lazy</code> generates a getter
that handles
+initialisation automatically, property access through the getter is
+always safe and won’t trigger null dereference warnings.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_example_6_going_strict_flow_sensitive_analysis">Example 6: going
strict — flow-sensitive analysis</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>The standard <code>NullChecker</code> only flags issues involving annotated
+code — unannotated code passes silently. The <code>StrictNullChecker</code>
+goes further, tracking nullability through assignments and control
+flow even without annotations:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions =
'groovy.typecheckers.StrictNullChecker')
+static main(args) {
+ def x = null
+ x.toString() // compile error
+}</code></pre>
+</div>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code>[Static type checking] - Potential
null dereference: 'x' may be null</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>The checker tracks nullability through ternary expressions, elvis
+expressions, method return values, and reassignments. Assigning a
+non-null value clears the nullable state:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@TypeChecked(extensions =
'groovy.typecheckers.StrictNullChecker')
+static main(args) {
+ def x = null
+ x = 'hello'
+ assert x.toString() == 'hello' // ok: reassigned non-null
+}</code></pre>
+</div>
+</div>
+<div class="paragraph">
+<p>This is ideal for new modules where you want comprehensive null
+coverage from the start, without annotating every declaration.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_annotation_compatibility">Annotation compatibility</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>The checker matches annotations by <em>simple name</em>, not by
fully-qualified
+class name. This means it works with annotations from any library:</p>
+</div>
+<table class="tableblock frame-all grid-all stretch">
+<colgroup>
+<col style="width: 40%;">
+<col style="width: 60%;">
+</colgroup>
+<thead>
+<tr>
+<th class="tableblock halign-left valign-top">Library</th>
+<th class="tableblock halign-left valign-top">Annotations</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td class="tableblock halign-left valign-top"><p class="tableblock"><a
href="https://jspecify.dev/";>JSpecify</a></p></td>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>@Nullable</code>, <code>@NullMarked</code>,
<code>@NullUnmarked</code></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-left valign-top"><p class="tableblock">JSR-305
(<code>javax.annotation</code>)</p></td>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>@Nullable</code>, <code>@Nonnull</code>,
<code>@ParametersAreNonnullByDefault</code></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-left valign-top"><p
class="tableblock">JetBrains</p></td>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>@Nullable</code>, <code>@NotNull</code></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-left valign-top"><p class="tableblock">SpotBugs /
FindBugs</p></td>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>@Nullable</code>, <code>@NonNull</code>,
<code>@NonNullByDefault</code></p></td>
+</tr>
+<tr>
+<td class="tableblock halign-left valign-top"><p class="tableblock">Checker
Framework</p></td>
+<td class="tableblock halign-left valign-top"><p
class="tableblock"><code>@Nullable</code>, <code>@NonNull</code>,
<code>@MonotonicNonNull</code></p></td>
+</tr>
+</tbody>
+</table>
+<div class="paragraph">
+<p>If you prefer not to add an external dependency, you can define
+your own minimal annotations — the checker only cares about the
+simple name:</p>
+</div>
+<div class="listingblock">
+<div class="content">
+<pre class="prettyprint highlight"><code
data-lang="groovy">@Target([ElementType.PARAMETER, ElementType.METHOD,
ElementType.FIELD])
+@Retention(RetentionPolicy.CLASS)
+@interface Nullable {}
+
+@Target([ElementType.PARAMETER, ElementType.METHOD, ElementType.FIELD])
+@Retention(RetentionPolicy.CLASS)
+@interface NonNull {}</code></pre>
+</div>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_how_this_compares_to_java_approaches">How this compares to Java
approaches</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>Java developers wanting compile-time null safety currently reach
+for external tools — the
+<a href="https://checkerframework.org/manual/#nullness-checker";>Checker
Framework</a>,
+<a href="https://errorprone.info/";>Error Prone</a>, or IDE-specific inspections
+(IntelliJ, Eclipse). Each brings its own setup, annotation flavour,
+and build integration.</p>
+</div>
+<div class="paragraph">
+<p>Groovy’s NullChecker offers several advantages:</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><strong>Zero setup.</strong> It’s a type-checking extension — add one
+annotation and you’re done. No annotation processor configuration,
+no extra compiler flags, no Gradle plugin.</p>
+</li>
+<li>
+<p><strong>Works with any annotation library.</strong> Simple-name matching
means
+you can use JSpecify, JSR-305, JetBrains, SpotBugs, Checker
+Framework, or your own — interchangeably.</p>
+</li>
+<li>
+<p><strong>Understands Groovy idioms.</strong> Safe navigation
(<code>?.</code>), elvis
+assignment (<code>?=</code>), <code>@Lazy</code> fields, and Groovy truth are
all
+recognised. A Java-only tool can’t help here.</p>
+</li>
+<li>
+<p><strong>Two-tier strictness.</strong> Start with annotation-only checking on
+existing code, then enable flow-sensitive mode for new modules —
+no all-or-nothing migration.</p>
+</li>
+<li>
+<p><strong>Complements <code>@NullCheck</code>.</strong> Catch violations at
compile time
+while keeping the runtime guard as a safety net.</p>
+</li>
+</ul>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_the_full_picture">The full picture</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>The examples above cover the most common scenarios. The complete
+proposal also includes detection of nullable method return value
+dereferences, <code>@Nullable</code> values flowing into <code>@NonNull</code>
parameters
+through variables, nullable propagation in ternary and elvis
+expressions, and integration with JSpecify’s <code>@NullMarked</code> /
+<code>@NullUnmarked</code> scoping. The full spec is available in the
+<a href="https://github.com/apache/groovy/pull/2426";>PR</a>.</p>
+</div>
+<div class="paragraph">
+<p>For complementary null-related checks — such as detecting broken
+null-check logic, unnecessary null guards before <code>instanceof</code>, or
+<code>Boolean</code> methods returning <code>null</code> — consider using
+<a href="https://codenarc.org/";>CodeNarc</a>'s null-related rules alongside
+these type checkers.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_wed_love_your_feedback">We’d love your feedback</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>The NullChecker feature is currently a proposal in
+<a href="https://github.com/apache/groovy/pull/2426";>PR #2426</a>
+(tracking issue
+<a href="https://issues.apache.org/jira/browse/GROOVY-11894";>GROOVY-11894</a>).
+Null safety is a foundational concern, and we want to get the
+design right.</p>
+</div>
+<div class="ulist">
+<ul>
+<li>
+<p><strong>Comment</strong> on the <a
href="https://github.com/apache/groovy/pull/2426";>PR</a> or
+the <a href="https://issues.apache.org/jira/browse/GROOVY-11894";>JIRA issue</a>
+with your thoughts, use cases, or design suggestions.</p>
+</li>
+<li>
+<p><strong>Vote</strong> on the JIRA issue if you’d like to see this
feature land.</p>
+</li>
+</ul>
+</div>
+<div class="paragraph">
+<p>Your feedback helps us gauge interest and shape the final design.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_conclusion">Conclusion</h2>
+<div class="sectionbody">
+<div class="paragraph">
+<p>Through our <em>Groovy Shelf</em> bookshop examples we’ve seen how the
+proposed NullChecker catches null dereferences, unsafe assignments,
+and missing null checks at compile time — from looking up books
+with nullable titles, to enforcing non-null parameters, recognising
+Groovy’s safe-navigation idioms, applying class-level defaults with
+<code>@NonNullByDefault</code>, handling lazy initialisation with
+<code>@MonotonicNonNull</code>, and tracking nullability through control flow
+with the <code>StrictNullChecker</code>. The setup is minimal, the annotation
+compatibility is broad, and the two-tier strictness model lets you
+adopt null safety at your own pace.</p>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_references">References</h2>
+<div class="sectionbody">
+<div class="ulist">
+<ul>
+<li>
+<p><a href="https://github.com/apache/groovy/pull/2426";>PR #2426 — NullChecker
type-checking extension</a></p>
+</li>
+<li>
+<p><a href="https://issues.apache.org/jira/browse/GROOVY-11894";>GROOVY-11894 —
Tracking issue</a></p>
+</li>
+<li>
+<p><a href="https://jspecify.dev/";>JSpecify — Standard Java annotations for
null safety</a></p>
+</li>
+<li>
+<p><a href="https://checkerframework.org/manual/#nullness-checker";>Checker
Framework — Nullness Checker</a></p>
+</li>
+<li>
+<p><a
href="https://groovy-lang.org/objectorientation.html#_safe_navigation_operator";>Groovy
safe navigation operator</a></p>
+</li>
+<li>
+<p><a href="https://codenarc.org/";>CodeNarc</a></p>
+</li>
+</ul>
+</div>
+</div>
+</div></div></div></div></div><footer id='footer'>
+ <div class='row'>
+ <div class='colset-3-footer'>
+ <div class='col-1'>
+ <h1>Groovy</h1><ul>
+ <li><a
href='https://groovy-lang.org/learn.html'>Learn</a></li><li><a
href='https://groovy-lang.org/documentation.html'>Documentation</a></li><li><a
href='/download.html'>Download</a></li><li><a
href='https://groovy-lang.org/support.html'>Support</a></li><li><a
href='/'>Contribute</a></li><li><a
href='https://groovy-lang.org/ecosystem.html'>Ecosystem</a></li><li><a
href='/blog'>Blog posts</a></li><li><a
href='https://groovy.apache.org/events.ht [...]
+ </ul>
+ </div><div class='col-2'>
+ <h1>About</h1><ul>
+ <li><a
href='https://github.com/apache/groovy'>Source code</a></li><li><a
href='https://groovy-lang.org/security.html'>Security</a></li><li><a
href='https://groovy-lang.org/learn.html#books'>Books</a></li><li><a
href='https://groovy-lang.org/thanks.html'>Thanks</a></li><li><a
href='http://www.apache.org/foundation/sponsorship.html'>Sponsorship</a></li><li><a
href='https://groovy-lang.org/faq.html'>FAQ</a></li><li><a
href='https://groovy-lang.or [...]
+ </ul>
+ </div><div class='col-3'>
+ <h1>Socialize</h1><ul>
+ <li><a
href='https://groovy-lang.org/mailing-lists.html'>Discuss on the mailing
list</a></li><li><a href='https://x.com/ApacheGroovy'>Groovy on
X</a></li><li><a href='https://bsky.app/profile/groovy.apache.org'>Groovy on
Bluesky</a></li><li><a href='https://fosstodon.org/@ApacheGroovy'>Groovy on
Mastodon</a></li><li><a
href='https://www.linkedin.com/company/106402668/admin/dashboard/'>Groovy on
LinkedIn</a></li><li><a href='https://groovy-lang. [...]
+ </ul>
+ </div><div class='col-right'>
+ <p>
+ The Groovy programming language is
supported by the <a href='https://www.apache.org'>Apache Software
Foundation</a> and the Groovy community.
+ </p><div text-align='right'>
+ <img
src='https://www.apache.org/img/asf_logo.png' title='The Apache Software
Foundation' alt='The Apache Software Foundation' style='width:60%'/>
+ </div><p>Apache, Apache Groovy,
Groovy, and the ASF logo are either registered trademarks or trademarks of The
Apache Software Foundation.</p>
+ </div>
+ </div><div class='clearfix'>© 2003-2026
the Apache Groovy project — Groovy is Open Source: <a
href='https://www.apache.org/licenses/LICENSE-2.0.html' alt='Apache 2
License'>license</a>, <a
href='https://privacy.apache.org/policies/privacy-policy-public.html'>privacy
policy</a>.</div>
+ </div>
+ </footer></div>
+ </div>
+ </div>
+ </div>
+ </div><script src='../js/vendor/jquery-1.10.2.min.js'
defer></script><script src='../js/vendor/classie.js' defer></script><script
src='../js/vendor/bootstrap.js' defer></script><script
src='../js/vendor/sidebarEffects.js' defer></script><script
src='../js/vendor/modernizr-2.6.2.min.js' defer></script><script
src='../js/plugins.js' defer></script><script
src='../js/vendor/prettify.min.js'></script><script>document.addEventListener('DOMContentLoaded',prettyPrint)</script>
+</body></html>
\ No newline at end of file
diff --git a/blog/index.html b/blog/index.html
index 4c10b01..5a61e3b 100644
--- a/blog/index.html
+++ b/blog/index.html
@@ -59,7 +59,7 @@
</ul>
</div>
</div>
- </div><div id='content' class='page-1'><div
class='row'><div class='row-fluid'><div class='col-lg-3' id='blog-index'><ul
class='nav-sidebar list'><li class='active'><a
href='/blog/'>Blogs</a></li><li><a href='groovy-async-await'>Async/await for
Groovy™</a></li><li><a href='loop-invariants'>Design by contract with
Groovy™: loop invariants</a></li><li><a
href='groovy-graph-databases'>Using Graph Databases with
Groovy™</a></li><li><a href='fruity-ec [...]
+ </div><div id='content' class='page-1'><div
class='row'><div class='row-fluid'><div class='col-lg-3' id='blog-index'><ul
class='nav-sidebar list'><li class='active'><a
href='/blog/'>Blogs</a></li><li><a href='groovy-null-checker'>Compile-time null
safety for Groovy™</a></li><li><a href='groovy-async-await'>Async/await
for Groovy™</a></li><li><a href='loop-invariants'>Design by contract with
Groovy™: loop invariants</a></li><li><a href='groovy-gra [...]
<div class='row'>
<div class='colset-3-footer'>
<div class='col-1'>
@@ -103,7 +103,7 @@
colors: am5.ColorSet.new(root, {})
}));
wc.data.setAll([
- { category: "groovy", value: 89 }, { category: "asf", value: 2
}, { category: "apachecon", value: 3 }, { category: "communityovercode", value:
2 }, { category: "natural language processing", value: 2 }, { category: "nlp",
value: 1 }, { category: "nlpcraft", value: 1 }, { category: "combinations",
value: 1 }, { category: "permutations", value: 1 }, { category: "testing",
value: 2 }, { category: "junit", value: 2 }, { category: "spock", value: 2 }, {
category: "jqwik", valu [...]
+ { category: "groovy", value: 89 }, { category: "asf", value: 2
}, { category: "apachecon", value: 3 }, { category: "communityovercode", value:
2 }, { category: "natural language processing", value: 2 }, { category: "nlp",
value: 1 }, { category: "nlpcraft", value: 1 }, { category: "combinations",
value: 1 }, { category: "permutations", value: 1 }, { category: "testing",
value: 2 }, { category: "junit", value: 2 }, { category: "spock", value: 2 }, {
category: "jqwik", valu [...]
]);
wc.labels.template.setAll({
paddingTop: 5,
diff --git a/search/search-index.json b/search/search-index.json
index a3c547b..40a2cd7 100644
--- a/search/search-index.json
+++ b/search/search-index.json
@@ -167,6 +167,13 @@
"url": "blog/groovy-gatherers.html",
"site": "dev"
},
+ {
+ "id": "blog/groovy-null-checker.html",
+ "title": "The Apache Groovy programming language - Blogs -
Compile-time null safety for Groovy™",
+ "content": "The Apache Groovy programming language - Blogs -
Compile-time null safety for Groovy™ Socialize Discuss on the mailing
list Groovy on X Groovy on Bluesky Groovy on Mastodon Groovy on LinkedIn Events
and conferences Source code on GitHub Report issues in Jira Stack Overflow
questions Slack Community You are using an outdated browser. Please upgrade
your browser to improve your experience. Apache Groovy™ Learn
Documentation Download Support Contribute Ecosys [...]
+ "url": "blog/groovy-null-checker.html",
+ "site": "dev"
+ },
{
"id": "blog/seasons-greetings-emoji.html",
"title": "The Apache Groovy programming language - Blogs -
Season’s Greetings with Emojis",
@@ -688,7 +695,7 @@
{
"id": "blog/index.html",
"title": "The Apache Groovy programming language - Blogs",
- "content": "The Apache Groovy programming language - Blogs Socialize
Discuss on the mailing list Groovy on X Groovy on Bluesky Groovy on Mastodon
Groovy on LinkedIn Events and conferences Source code on GitHub Report issues
in Jira Stack Overflow questions Slack Community You are using an outdated
browser. Please upgrade your browser to improve your experience. Apache
Groovy™ Learn Documentation Download Support Contribute Ecosystem Blog
posts Socialize Blogs Async/await fo [...]
+ "content": "The Apache Groovy programming language - Blogs Socialize
Discuss on the mailing list Groovy on X Groovy on Bluesky Groovy on Mastodon
Groovy on LinkedIn Events and conferences Source code on GitHub Report issues
in Jira Stack Overflow questions Slack Community You are using an outdated
browser. Please upgrade your browser to improve your experience. Apache
Groovy™ Learn Documentation Download Support Contribute Ecosystem Blog
posts Socialize Blogs Compile-time n [...]
"url": "blog/index.html",
"site": "dev"
},
