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<div class="sub-title"><span class="package-label-in-type">Package</span>&nbsp;<a href="package-summary.html">org.apache.calcite.linq4j.function</a></div>
<h1 title="Annotation Type Parameter" class="title">Annotation Type Parameter</h1>
</div>
<section class="class-description" id="class-description">
<hr>
<div class="type-signature"><span class="annotations"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/annotation/Retention.html" title="class or interface in java.lang.annotation" class="external-link">@Retention</a>(<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/annotation/RetentionPolicy.html#RUNTIME" title="class or interface in java.lang.annotation" class="external-link">RUNTIME</a>)
<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/annotation/Target.html" title="class or interface in java.lang.annotation" class="external-link">@Target</a>(<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/annotation/ElementType.html#PARAMETER" title="class or interface in java.lang.annotation" class="external-link">PARAMETER</a>)
</span><span class="modifiers">public @interface </span><span class="element-name type-name-label">Parameter</span></div>
<div class="block">Annotation that supplies metadata about a function parameter.
<p>A typical use is to derive names for the parameters of user-defined
functions.
<p>Here is an example:
<blockquote><pre>
public static class MyLeftFunction {
public String eval(
&#64;Parameter(name = "s") String s,
&#64;Parameter(name = "n", optional = true) Integer n) {
return s.substring(0, n == null ? 1 : n);
}
}</pre></blockquote>
<p>The first parameter is named "s" and is mandatory,
and the second parameter is named "n" and is optional.
<p>If this annotation is present, it supersedes information that might be
available via
<code>Executable.getParameters()</code> (JDK 1.8 and above).
<p>If the annotation is not specified, parameters will be named "arg0",
"arg1" et cetera, and will be mandatory.</div>
</section>
<section class="summary">
<ul class="summary-list">
<!-- =========== ANNOTATION TYPE REQUIRED MEMBER SUMMARY =========== -->
<li>
<section class="member-summary" id="annotation-interface-required-element-summary">
<h2>Required Element Summary</h2>
<div class="caption"><span>Required Elements</span></div>
<div class="summary-table three-column-summary">
<div class="table-header col-first">Modifier and Type</div>
<div class="table-header col-second">Required Element</div>
<div class="table-header col-last">Description</div>
<div class="col-first even-row-color"><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></code></div>
<div class="col-second even-row-color"><code><a href="#name()" class="member-name-link">name</a></code></div>
<div class="col-last even-row-color">
<div class="block">The name of the parameter.</div>
</div>
</div>
</section>
</li>
<!-- =========== ANNOTATION TYPE OPTIONAL MEMBER SUMMARY =========== -->
<li>
<section class="member-summary" id="annotation-interface-optional-element-summary">
<h2>Optional Element Summary</h2>
<div class="caption"><span>Optional Elements</span></div>
<div class="summary-table three-column-summary">
<div class="table-header col-first">Modifier and Type</div>
<div class="table-header col-second">Optional Element</div>
<div class="table-header col-last">Description</div>
<div class="col-first even-row-color"><code>boolean</code></div>
<div class="col-second even-row-color"><code><a href="#optional()" class="member-name-link">optional</a></code></div>
<div class="col-last even-row-color">
<div class="block">Returns whether the parameter is optional.</div>
</div>
</div>
</section>
</li>
</ul>
</section>
<section class="details" id="annotation-interface-element-detail">
<ul class="details-list">
<!-- ============ ANNOTATION TYPE MEMBER DETAIL =========== -->
<li>
<section class="member-details">
<h2>Element Details</h2>
<ul class="member-list">
<li>
<section class="detail" id="name()">
<h3>name</h3>
<div class="member-signature"><span class="return-type"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></span>&nbsp;<span class="element-name">name</span></div>
<div class="block">The name of the parameter.
<p>The name is used when the function is called
with parameter assignment, for example <code>foo(x =&gt; 1, y =&gt; 'a')</code>.</div>
</section>
</li>
</ul>
</section>
</li>
<!-- ============ ANNOTATION TYPE MEMBER DETAIL =========== -->
<li>
<section class="member-details">
<ul class="member-list">
<li>
<section class="detail" id="optional()">
<h3>optional</h3>
<div class="member-signature"><span class="return-type">boolean</span>&nbsp;<span class="element-name">optional</span></div>
<div class="block">Returns whether the parameter is optional.
<p>An optional parameter does not need to be specified when you call the
function.
<p>If you call a function using positional parameter syntax, you can omit
optional parameters on the trailing edge. For example, if you have a
function
<code>baz(int a, int b optional, int c, int d optional, int e optional)</code>
then you can call <code>baz(a, b, c, d, e)</code>
or <code>baz(a, b, c, d)</code>
or <code>baz(a, b, c)</code>
but not <code>baz(a, b)</code> because <code>c</code> is not optional.
<p>If you call a function using parameter name assignment syntax, you can
omit any parameter that has a default value. For example, you can call
<code>baz(a =&gt; 1, e =&gt; 5, c =&gt; 3)</code>, omitting optional parameters <code>b</code>
and <code>d</code>.
<p>Currently, the default value used when a parameter is not specified
is NULL, and therefore optional parameters must be nullable.</div>
<dl class="notes">
<dt>Default:</dt>
<dd>false</dd>
</dl>
</section>
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