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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</a></div>
<h1 title="Class Extensions" class="title">Class Extensions</h1>
</div>
<div class="inheritance" title="Inheritance Tree"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">java.lang.Object</a>
<div class="inheritance">org.apache.calcite.linq4j.Extensions</div>
</div>
<section class="class-description" id="class-description">
<hr>
<div class="type-signature"><span class="modifiers">public abstract class </span><span class="element-name type-name-label">Extensions</span>
<span class="extends-implements">extends <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">Object</a></span></div>
<div class="block">Contains what, in LINQ.NET, would be extension methods.
<h2>Notes on mapping from LINQ.NET to Java</h2>
<p>We have preserved most of the API. But we've changed a few things, so that
the API is more typical Java API:</p>
<ul>
<li>Java method names start with a lower-case letter.</li>
<li>A few methods became keywords when their first letter was converted
to lower case; hence
<a href="tree/Expressions.html#break_(org.apache.calcite.linq4j.tree.LabelTarget)"><code>Expressions.break_(org.apache.calcite.linq4j.tree.LabelTarget)</code></a></li>
<li>We created a Java interface <a href="Enumerable.html" title="interface in org.apache.calcite.linq4j"><code>Enumerable</code></a>, similar to LINQ.NET's
IEnumerable. IEnumerable is built into C#, and that gives it
advantages: the standard collections implement it, and you can use
any IEnumerable in a foreach loop. We made the Java
<code>Enumerable</code> extend <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Iterable.html" title="class or interface in java.lang" class="external-link"><code>Iterable</code></a>,
so that it can be used in for-each loops. But the standard
collections still don't implement it. A few methods that take an
IEnumerable in LINQ.NET take an Iterable in LINQ4J.</li>
<li>LINQ.NET's Dictionary interface maps to Map in Java;
hence, the LINQ.NET <code>ToDictionary</code> methods become
<code>toMap</code>.</li>
<li>LINQ.NET's decimal type changes to BigDecimal. (A little bit unnatural,
since decimal is primitive and BigDecimal is not.)</li>
<li>There is no Nullable in Java. Therefore we distinguish between methods
that return, say, Long (which may be null) and long. See for example
<a href="function/NullableLongFunction1.html" title="interface in org.apache.calcite.linq4j.function"><code>NullableLongFunction1</code></a> and
<a href="function/LongFunction1.html" title="interface in org.apache.calcite.linq4j.function"><code>LongFunction1</code></a>, and the
variants of <a href="ExtendedEnumerable.html#sum(org.apache.calcite.linq4j.function.BigDecimalFunction1)"><code>ExtendedEnumerable.sum(org.apache.calcite.linq4j.function.BigDecimalFunction1&lt;TSource&gt;)</code></a> that call them.
<li>Java erases type parameters from argument types before resolving
overloading. Therefore similar methods have the same erasure. Methods
<code>averageDouble</code>,
<code>averageInteger</code>,
<code>groupByK</code>,
<code>selectN</code>,
<code>selectManyN</code>,
<code>skipWhileN</code>,
<code>sumBigDecimal</code>,
<code>sumNullableBigDecimal</code>,
<code>whereN</code>
have been renamed from <code>average</code>, <code>groupBy</code>, <code>max</code>,
<code>min</code>, <code>select</code>, <code>selectMany</code>, <code>skipWhile</code> and
<code>where</code> to prevent ambiguity.</li>
<li>.NET allows <i>extension methods</i> &mdash; static methods that then
become, via compiler magic, a method of any object whose type is the
same as the first parameter of the extension method. In LINQ.NET, the
<code>IQueryable</code> and <code>IEnumerable</code> interfaces have many such methods.
In Java, those methods need to be explicitly added to the interface, and will
need to be implemented by every class that implements that interface.
We can help by implementing the methods as static methods, and by
providing an abstract base class that implements the extension methods
in the interface. Hence <a href="AbstractEnumerable.html" title="class in org.apache.calcite.linq4j"><code>AbstractEnumerable</code></a> and
<a href="AbstractQueryable.html" title="class in org.apache.calcite.linq4j"><code>AbstractQueryable</code></a> call methods in <a href="Extensions.html" title="class in org.apache.calcite.linq4j"><code>Extensions</code></a>.</li>
<li>.NET Func becomes <a href="function/Function0.html" title="interface in org.apache.calcite.linq4j.function"><code>Function0</code></a>,
<a href="function/Function1.html" title="interface in org.apache.calcite.linq4j.function"><code>Function1</code></a>,
<a href="function/Function2.html" title="interface in org.apache.calcite.linq4j.function"><code>Function2</code></a>, depending
on the number of arguments to the function, because Java types cannot be
overloaded based on the number of type parameters.</li>
<li>Types map as follows:
<code>Int32</code> &rarr; <code>int</code> or <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Integer.html" title="class or interface in java.lang" class="external-link"><code>Integer</code></a>,
<code>Int64</code> &rarr; <code>long</code> or <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Long.html" title="class or interface in java.lang" class="external-link"><code>Long</code></a>,
<code>bool</code> &rarr; <code>boolean</code> or <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Boolean.html" title="class or interface in java.lang" class="external-link"><code>Boolean</code></a>,
<code>Dictionary</code> &rarr; <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/Map.html" title="class or interface in java.util" class="external-link"><code>Map</code></a>,
<code>Lookup</code> &rarr; <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/Map.html" title="class or interface in java.util" class="external-link"><code>Map</code></a> whose value type is an <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Iterable.html" title="class or interface in java.lang" class="external-link"><code>Iterable</code></a>,
</li>
<li>Function types that accept primitive types in LINQ.NET have become
boxed types in LINQ4J. For example, a predicate function
<code>Func&lt;T, bool&gt;</code> becomes <code>Func1&lt;T, Boolean&gt;</code>.
It would be wrong to infer that the function is allowed to return null.</li>
</ul></div>
</section>
<section class="summary">
<ul class="summary-list">
<!-- ========== METHOD SUMMARY =========== -->
<li>
<section class="method-summary" id="method-summary">
<h2>Method Summary</h2>
<div id="method-summary-table">
<div class="table-tabs" role="tablist" aria-orientation="horizontal"><button id="method-summary-table-tab0" role="tab" aria-selected="true" aria-controls="method-summary-table.tabpanel" tabindex="0" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table', 3)" class="active-table-tab">All Methods</button><button id="method-summary-table-tab1" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab1', 3)" class="table-tab">Static Methods</button><button id="method-summary-table-tab4" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab4', 3)" class="table-tab">Concrete Methods</button></div>
<div id="method-summary-table.tabpanel" role="tabpanel">
<div class="summary-table three-column-summary" aria-labelledby="method-summary-table-tab0">
<div class="table-header col-first">Modifier and Type</div>
<div class="table-header col-second">Method</div>
<div class="table-header col-last">Description</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static &lt;T&gt;&nbsp;<a href="Queryable.html" title="interface in org.apache.calcite.linq4j">Queryable</a>&lt;T&gt;</code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#asQueryable(org.apache.calcite.linq4j.DefaultEnumerable)" class="member-name-link">asQueryable</a><wbr>(<a href="DefaultEnumerable.html" title="class in org.apache.calcite.linq4j">DefaultEnumerable</a>&lt;T&gt;&nbsp;source)</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">&nbsp;</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/RuntimeException.html" title="class or interface in java.lang" class="external-link">RuntimeException</a></code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#todo()" class="member-name-link">todo</a>()</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">&nbsp;</div>
</div>
</div>
</div>
<div class="inherited-list">
<h3 id="methods-inherited-from-class-java.lang.Object">Methods inherited from class&nbsp;java.lang.<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">Object</a></h3>
<code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#clone()" title="class or interface in java.lang" class="external-link">clone</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#equals(java.lang.Object)" title="class or interface in java.lang" class="external-link">equals</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#finalize()" title="class or interface in java.lang" class="external-link">finalize</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#getClass()" title="class or interface in java.lang" class="external-link">getClass</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#hashCode()" title="class or interface in java.lang" class="external-link">hashCode</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#notify()" title="class or interface in java.lang" class="external-link">notify</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#notifyAll()" title="class or interface in java.lang" class="external-link">notifyAll</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#toString()" title="class or interface in java.lang" class="external-link">toString</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#wait()" title="class or interface in java.lang" class="external-link">wait</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#wait(long)" title="class or interface in java.lang" class="external-link">wait</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#wait(long,int)" title="class or interface in java.lang" class="external-link">wait</a></code></div>
</section>
</li>
</ul>
</section>
<section class="details">
<ul class="details-list">
<!-- ============ METHOD DETAIL ========== -->
<li>
<section class="method-details" id="method-detail">
<h2>Method Details</h2>
<ul class="member-list">
<li>
<section class="detail" id="todo()">
<h3>todo</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/RuntimeException.html" title="class or interface in java.lang" class="external-link">RuntimeException</a></span>&nbsp;<span class="element-name">todo</span>()</div>
</section>
</li>
<li>
<section class="detail" id="asQueryable(org.apache.calcite.linq4j.DefaultEnumerable)">
<h3>asQueryable</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="type-parameters">&lt;T&gt;</span>&nbsp;<span class="return-type"><a href="Queryable.html" title="interface in org.apache.calcite.linq4j">Queryable</a>&lt;T&gt;</span>&nbsp;<span class="element-name">asQueryable</span><wbr><span class="parameters">(<a href="DefaultEnumerable.html" title="class in org.apache.calcite.linq4j">DefaultEnumerable</a>&lt;T&gt;&nbsp;source)</span></div>
</section>
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</section>
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