Package org.apache.calcite.linq4j

Class Linq4j

java.lang.Object

org.apache.calcite.linq4j.Linq4j

public abstract class Linq4j
extends Object

Utility and factory methods for Linq4j.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	Linq4j.CartesianProductListEnumerator<E>	Enumerates over the cartesian product of the given lists, returning a list for each row.
(package private) static class	Linq4j.CollectionEnumerable<T>	Collection enumerable.
(package private) static class	Linq4j.CompositeEnumerable<E>	Composite enumerable.
private static class	Linq4j.EnumeratorIterator<T>	Iterator that reads from an underlying Enumerator.
(package private) static class	Linq4j.IterableEnumerable<T>	Iterable enumerable.
(package private) static class	Linq4j.IterableEnumerator<T>	Iterable enumerator.
(package private) static class	Linq4j.ListEnumerable<T>	List enumerable.
private static class	Linq4j.ListEnumerator<V>	Enumerator optimized for random-access list.
private static class	Linq4j.SingletonEnumerator<E>	Enumerator that returns one element.
private static class	Linq4j.SingletonNullEnumerator<E>	Enumerator that returns one null element.

Field Summary

Fields

Modifier and Type	Field	Description
static QueryProvider	DEFAULT_PROVIDER	Query provider that simply executes a Queryable by calling its enumerator method; does not attempt optimization.
private static Object	DUMMY
static Enumerable<?>	EMPTY_ENUMERABLE
private static Enumerator<Object>	EMPTY_ENUMERATOR

Constructor Summary

Constructors

Modifier	Constructor	Description
private	Linq4j()

Method Summary

Modifier and Type	Method	Description
static <T> Enumerable<T>	asEnumerable(Iterable<T> iterable)	Adapter that converts an Iterable into an Enumerable.
static <T> Enumerable<T>	asEnumerable(Collection<T> collection)	Adapter that converts an Collection into an Enumerable.
static <T> Enumerable<T>	asEnumerable(List<T> list)	Adapter that converts an List into an Enumerable.
static <T> Enumerable<T>	asEnumerable(T[] ts)	Adapter that converts an array into an enumerable.
static <TSource,TResult> Enumerable<TResult>	cast(Iterable<TSource> source, Class<TResult> clazz)	Converts the elements of a given Iterable to the specified type.
private static <T> void	closeIterator(Iterator<T> iterator)	Closes an iterator, if it can be closed.
static <E> Enumerable<E>	concat(List<Enumerable<E>> enumerableList)	Concatenates two or more Enumerables to form a composite enumerable that contains the union of their elements.
static <T> Enumerable<T>	emptyEnumerable()	Returns an Enumerable that has no elements.
static <T> Enumerator<T>	emptyEnumerator()	Returns an Enumerator that has no elements.
static <V> Enumerator<V>	enumerator(Collection<? extends V> values)	Adapter that converts a collection into an enumerator.
static <T> Iterator<T>	enumeratorIterator(Enumerator<T> enumerator)	Adapter that converts an enumerator into an iterator.
static <T> boolean	equals(T t0, T t1)	Deprecated.
static Method	getMethod(String className, String methodName, Class... parameterTypes)
static <T> Enumerator<T>	iterableEnumerator(Iterable<? extends T> iterable)	Adapter that converts an iterable into an enumerator.
private static <V> Enumerator<V>	listEnumerator(List<? extends V> list)
static <TSource,TResult> Enumerable<TResult>	ofType(Iterable<TSource> source, Class<TResult> clazz)	Returns elements of a given Iterable that are of the specified type.
static <T> Iterable<List<T>>	product(Iterable<? extends Iterable<T>> iterables)	Returns the cartesian product of an iterable of iterables.
static <T> Enumerator<List<T>>	product(List<Enumerator<T>> enumerators)	Returns an enumerator that is the cartesian product of the given enumerators.
static <T> T	requireNonNull(T o)	Deprecated.
static <T> Enumerable<T>	singletonEnumerable(T element)	Returns an Enumerable that has one element.
static <T> Enumerator<T>	singletonEnumerator(T element)	Returns an Enumerator that has one element.
static <T> Enumerator<T>	singletonNullEnumerator()	Returns an Enumerator that has one null element.
static <F,E> Enumerator<E>	transform(Enumerator<F> enumerator, Function1<F,E> func)	Applies a function to each element of an Enumerator.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DUMMY

private static final Object DUMMY

DEFAULT_PROVIDER

public static final QueryProvider DEFAULT_PROVIDER

Query provider that simply executes a Queryable by calling its enumerator method; does not attempt optimization.

EMPTY_ENUMERATOR

private static final Enumerator<Object> EMPTY_ENUMERATOR

EMPTY_ENUMERABLE

public static final Enumerable<?> EMPTY_ENUMERABLE

Constructor Detail

Linq4j

private Linq4j()

Method Detail

getMethod

public static Method getMethod(String className,
                               String methodName,
                               Class... parameterTypes)

enumeratorIterator

public static <T> Iterator<T> enumeratorIterator(Enumerator<T> enumerator)

Adapter that converts an enumerator into an iterator.

WARNING: The iterator returned by this method does not call Enumerator.close(), so it is not safe to use with an enumerator that allocates resources.

Type Parameters:

T - Element type

Parameters:

enumerator - Enumerator

Returns:

Iterator

iterableEnumerator

public static <T> Enumerator<T> iterableEnumerator(Iterable<? extends T> iterable)

Adapter that converts an iterable into an enumerator.

Type Parameters:

T - Element type

Parameters:

iterable - Iterable

Returns:

enumerator

asEnumerable

public static <T> Enumerable<T> asEnumerable(List<T> list)

Adapter that converts an List into an Enumerable.

Type Parameters:

T - Element type

Parameters:

list - List

Returns:

enumerable

asEnumerable

public static <T> Enumerable<T> asEnumerable(Collection<T> collection)

Adapter that converts an Collection into an Enumerable.

It uses more efficient implementations if the iterable happens to be a List.

Type Parameters:

T - Element type

Parameters:

collection - Collection

Returns:

enumerable

asEnumerable

public static <T> Enumerable<T> asEnumerable(Iterable<T> iterable)

Adapter that converts an Iterable into an Enumerable.

It uses more efficient implementations if the iterable happens to be a Collection or a List.

Type Parameters:

T - Element type

Parameters:

iterable - Iterable

Returns:

enumerable

asEnumerable

public static <T> Enumerable<T> asEnumerable(T[] ts)

Adapter that converts an array into an enumerable.

Type Parameters:

T - Element type

Parameters:

ts - Array

Returns:

enumerable

enumerator

public static <V> Enumerator<V> enumerator(Collection<? extends V> values)

Adapter that converts a collection into an enumerator.

Type Parameters:

V - Element type

Parameters:

values - Collection

Returns:

Enumerator over the collection

listEnumerator

private static <V> Enumerator<V> listEnumerator(List<? extends V> list)

transform

public static <F,E> Enumerator<E> transform(Enumerator<F> enumerator,
                                            Function1<F,E> func)

Applies a function to each element of an Enumerator.

Type Parameters:

F - Backing element type

E - Element type

Parameters:

enumerator - Backing enumerator

func - Transform function

Returns:

Enumerator

cast

public static <TSource,TResult> Enumerable<TResult> cast(Iterable<TSource> source,
                                                         Class<TResult> clazz)

Converts the elements of a given Iterable to the specified type.

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its RawEnumerable.enumerator() method directly or by using for (... in ...).

Since standard Java Collection objects implement the Iterable interface, the cast method enables the standard query operators to be invoked on collections (including List and Set) by supplying the necessary type information. For example, ArrayList does not implement Enumerable<F>, but you can invoke

Linq4j.cast(list, Integer.class)

to convert the list of an enumerable that can be queried using the standard query operators.

If an element cannot be cast to type <TResult>, this method will throw a ClassCastException. To obtain only those elements that can be cast to type TResult, use the ofType(java.lang.Iterable<TSource>, java.lang.Class<TResult>) method instead.

See Also:

ExtendedEnumerable.cast(Class), ofType(java.lang.Iterable<TSource>, java.lang.Class<TResult>), asEnumerable(Iterable)

ofType

public static <TSource,TResult> Enumerable<TResult> ofType(Iterable<TSource> source,
                                                           Class<TResult> clazz)

Returns elements of a given Iterable that are of the specified type.

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its RawEnumerable.enumerator() method directly or by using for (... in ...).

The ofType method returns only those elements in source that can be cast to type TResult. To instead receive an exception if an element cannot be cast to type TResult, use cast(Iterable, Class).

Since standard Java Collection objects implement the Iterable interface, the cast method enables the standard query operators to be invoked on collections (including List and Set) by supplying the necessary type information. For example, ArrayList does not implement Enumerable<F>, but you can invoke

Linq4j.ofType(list, Integer.class)

to convert the list of an enumerable that can be queried using the standard query operators.

See Also:

ExtendedEnumerable.cast(Class), cast(java.lang.Iterable<TSource>, java.lang.Class<TResult>)

singletonEnumerable

public static <T> Enumerable<T> singletonEnumerable(T element)

Returns an Enumerable that has one element.

Type Parameters:

T - Element type

Returns:

Singleton enumerable

singletonEnumerator

public static <T> Enumerator<T> singletonEnumerator(T element)

Returns an Enumerator that has one element.

Type Parameters:

T - Element type

Returns:

Singleton enumerator

singletonNullEnumerator

public static <T> Enumerator<T> singletonNullEnumerator()

Returns an Enumerator that has one null element.

Type Parameters:

T - Element type

Returns:

Singleton enumerator

emptyEnumerable

public static <T> Enumerable<T> emptyEnumerable()

Returns an Enumerable that has no elements.

Type Parameters:

T - Element type

Returns:

Empty enumerable

emptyEnumerator

public static <T> Enumerator<T> emptyEnumerator()

Returns an Enumerator that has no elements.

Type Parameters:

T - Element type

Returns:

Empty enumerator

concat

public static <E> Enumerable<E> concat(List<Enumerable<E>> enumerableList)

Concatenates two or more Enumerables to form a composite enumerable that contains the union of their elements.

Type Parameters:

E - Element type

Parameters:

enumerableList - List of enumerable objects

Returns:

Composite enumerator

product

public static <T> Enumerator<List<T>> product(List<Enumerator<T>> enumerators)

Returns an enumerator that is the cartesian product of the given enumerators.

For example, given enumerator A that returns {"a", "b", "c"} and enumerator B that returns {"x", "y"}, product(List(A, B)) will return {List("a", "x"), List("a", "y"), List("b", "x"), List("b", "y"), List("c", "x"), List("c", "y")}.

Notice that the cardinality of the result is the product of the cardinality of the inputs. The enumerators A and B have 3 and 2 elements respectively, and the result has 3 * 2 = 6 elements. This is always the case. In particular, if any of the enumerators is empty, the result is empty.

Type Parameters:

T - Element type

Parameters:

enumerators - List of enumerators

Returns:

Enumerator over the cartesian product

product

public static <T> Iterable<List<T>> product(Iterable<? extends Iterable<T>> iterables)

Returns the cartesian product of an iterable of iterables.

equals

@Deprecated
public static <T> boolean equals(T t0,
                                 T t1)

Deprecated.

Returns whether the arguments are equal to each other.

Equivalent to Objects.equals(java.lang.Object, java.lang.Object) in JDK 1.7 and above.

requireNonNull

@Deprecated
public static <T> T requireNonNull(T o)

Deprecated.

Throws NullPointerException if argument is null, otherwise returns argument.

Equivalent to Objects.requireNonNull(T) in JDK 1.7 and above.

closeIterator

private static <T> void closeIterator(Iterator<T> iterator)

Closes an iterator, if it can be closed.