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| <div class="subTitle">org.apache.calcite.linq4j</div> |
| <h2 title="Class Extensions" class="title">Class Extensions</h2> |
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| <pre>public abstract class <span class="typeNameLabel">Extensions</span> |
| extends <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></pre> |
| <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="../../../../org/apache/calcite/linq4j/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="../../../../org/apache/calcite/linq4j/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/javase/8/docs/api/java/lang/Iterable.html?is-external=true" title="class or interface in java.lang"><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="../../../../org/apache/calcite/linq4j/function/NullableLongFunction1.html" title="interface in org.apache.calcite.linq4j.function"><code>NullableLongFunction1</code></a> and |
| <a href="../../../../org/apache/calcite/linq4j/function/LongFunction1.html" title="interface in org.apache.calcite.linq4j.function"><code>LongFunction1</code></a>, and the |
| variants of <a href="../../../../org/apache/calcite/linq4j/ExtendedEnumerable.html#sum-org.apache.calcite.linq4j.function.BigDecimalFunction1-"><code>ExtendedEnumerable.sum(org.apache.calcite.linq4j.function.BigDecimalFunction1<TSource>)</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> — 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="../../../../org/apache/calcite/linq4j/AbstractEnumerable.html" title="class in org.apache.calcite.linq4j"><code>AbstractEnumerable</code></a> and |
| <a href="../../../../org/apache/calcite/linq4j/AbstractQueryable.html" title="class in org.apache.calcite.linq4j"><code>AbstractQueryable</code></a> call methods in <a href="../../../../org/apache/calcite/linq4j/Extensions.html" title="class in org.apache.calcite.linq4j"><code>Extensions</code></a>.</li> |
| |
| <li>.NET Func becomes <a href="../../../../org/apache/calcite/linq4j/function/Function0.html" title="interface in org.apache.calcite.linq4j.function"><code>Function0</code></a>, |
| <a href="../../../../org/apache/calcite/linq4j/function/Function1.html" title="interface in org.apache.calcite.linq4j.function"><code>Function1</code></a>, |
| <a href="../../../../org/apache/calcite/linq4j/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> → <code>int</code> or <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html?is-external=true" title="class or interface in java.lang"><code>Integer</code></a>, |
| <code>Int64</code> → <code>long</code> or <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Long.html?is-external=true" title="class or interface in java.lang"><code>Long</code></a>, |
| <code>bool</code> → <code>boolean</code> or <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Boolean.html?is-external=true" title="class or interface in java.lang"><code>Boolean</code></a>, |
| <code>Dictionary</code> → <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Map.html?is-external=true" title="class or interface in java.util"><code>Map</code></a>, |
| <code>Lookup</code> → <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Map.html?is-external=true" title="class or interface in java.util"><code>Map</code></a> whose value type is an <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Iterable.html?is-external=true" title="class or interface in java.lang"><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> |
| </li> |
| </ul> |
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| <h3>Method Summary</h3> |
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| <caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t1" class="tableTab"><span><a href="javascript:show(1);">Static Methods</a></span><span class="tabEnd"> </span></span><span id="t4" class="tableTab"><span><a href="javascript:show(8);">Concrete Methods</a></span><span class="tabEnd"> </span></span></caption> |
| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colLast" scope="col">Method and Description</th> |
| </tr> |
| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code>static <T> <a href="../../../../org/apache/calcite/linq4j/Queryable.html" title="interface in org.apache.calcite.linq4j">Queryable</a><T></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/calcite/linq4j/Extensions.html#asQueryable-org.apache.calcite.linq4j.DefaultEnumerable-">asQueryable</a></span>(<a href="../../../../org/apache/calcite/linq4j/DefaultEnumerable.html" title="class in org.apache.calcite.linq4j">DefaultEnumerable</a><T> source)</code> </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/RuntimeException.html?is-external=true" title="class or interface in java.lang">RuntimeException</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/calcite/linq4j/Extensions.html#todo--">todo</a></span>()</code> </td> |
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| <h3>Methods inherited from class java.lang.<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></h3> |
| <code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#clone--" title="class or interface in java.lang">clone</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#equals-java.lang.Object-" title="class or interface in java.lang">equals</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#finalize--" title="class or interface in java.lang">finalize</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#getClass--" title="class or interface in java.lang">getClass</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#hashCode--" title="class or interface in java.lang">hashCode</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#notify--" title="class or interface in java.lang">notify</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#notifyAll--" title="class or interface in java.lang">notifyAll</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#toString--" title="class or interface in java.lang">toString</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait--" title="class or interface in java.lang">wait</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait-long-" title="class or interface in java.lang">wait</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait-long-int-" title="class or interface in java.lang">wait</a></code></li> |
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| <h4>todo</h4> |
| <pre>public static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/RuntimeException.html?is-external=true" title="class or interface in java.lang">RuntimeException</a> todo()</pre> |
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| <h4>asQueryable</h4> |
| <pre>public static <T> <a href="../../../../org/apache/calcite/linq4j/Queryable.html" title="interface in org.apache.calcite.linq4j">Queryable</a><T> asQueryable(<a href="../../../../org/apache/calcite/linq4j/DefaultEnumerable.html" title="class in org.apache.calcite.linq4j">DefaultEnumerable</a><T> source)</pre> |
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