org.apache.commons.collections4.FluentIterable Maven / Gradle / Ivy
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* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.collections4;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import org.apache.commons.collections4.iterators.SingletonIterator;
/**
* A FluentIterable provides a powerful yet simple API for manipulating
* Iterable instances in a fluent manner.
*
* A FluentIterable can be created either from an Iterable or from a set
* of elements. The following types of methods are provided:
*
*
* - fluent methods which return a new {@code FluentIterable} instance,
* providing a view of the original iterable (e.g. filter(Predicate));
*
- conversion methods which copy the FluentIterable's contents into a
* new collection or array (e.g. toList());
*
- utility methods which answer questions about the FluentIterable's
* contents (e.g. size(), anyMatch(Predicate)).
*
-
*
*
* The following example outputs the first 3 even numbers in the range [1, 10]
* into a list:
*
*
* List<String> result =
* FluentIterable
* .of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
* .filter(new Predicate<Integer>() {
* public boolean evaluate(Integer number) {
* return number % 2 == 0;
* }
* )
* .transform(TransformerUtils.stringValueTransformer())
* .limit(3)
* .toList();
*
* The resulting list will contain the following elements:
* [2, 4, 6]
*
* @param the element type
* @since 4.1
*/
public class FluentIterable implements Iterable {
/** A reference to the wrapped iterable. */
private final Iterable iterable;
// Static factory methods
// ----------------------------------------------------------------------
/**
* Creates a new empty FluentIterable.
*
* @param the element type
* @return a new empty FluentIterable
*/
public static FluentIterable empty() {
return IterableUtils.EMPTY_ITERABLE;
}
/**
* Creates a new FluentIterable of the single provided element.
*
* The returned iterable's iterator does not support {@code remove()}.
*
* @param the element type
* @param singleton the singleton element
* @return a new FluentIterable containing the singleton
*/
public static FluentIterable of(final T singleton) {
return of(IteratorUtils.asIterable(new SingletonIterator<>(singleton, false)));
}
/**
* Creates a new FluentIterable from the provided elements.
*
* The returned iterable's iterator does not support {@code remove()}.
*
* @param the element type
* @param elements the elements to be contained in the FluentIterable
* @return a new FluentIterable containing the provided elements
*/
public static FluentIterable of(final T... elements) {
return of(Arrays.asList(elements));
}
/**
* Construct a new FluentIterable from the provided iterable. If the
* iterable is already an instance of FluentIterable, the instance
* will be returned instead.
*
* The returned iterable's iterator supports {@code remove()} when the
* corresponding input iterator supports it.
*
* @param the element type
* @param iterable the iterable to wrap into a FluentIterable, may not be null
* @return a new FluentIterable wrapping the provided iterable
* @throws NullPointerException if iterable is null
*/
public static FluentIterable of(final Iterable iterable) {
IterableUtils.checkNotNull(iterable);
if (iterable instanceof FluentIterable) {
return (FluentIterable) iterable;
}
return new FluentIterable<>(iterable);
}
// Constructor
// ----------------------------------------------------------------------
/**
* Package-private constructor, used by IterableUtils.
*/
FluentIterable() {
this.iterable = this;
}
/**
* Create a new FluentIterable by wrapping the provided iterable.
* @param iterable the iterable to wrap
*/
private FluentIterable(final Iterable iterable) {
this.iterable = iterable;
}
// fluent construction methods
// ----------------------------------------------------------------------
/**
* Returns a new FluentIterable whose iterator will first traverse
* the elements of the current iterable, followed by the provided
* elements.
*
* @param elements the elements to append to the iterable
* @return a new iterable, combining this iterable with the elements
*/
public FluentIterable append(final E... elements) {
return append(Arrays.asList(elements));
}
/**
* Returns a new FluentIterable whose iterator will first traverse
* the elements of the current iterable, followed by the elements
* of the provided iterable.
*
* @param other the other iterable to combine, may not be null
* @return a new iterable, combining this iterable with other
* @throws NullPointerException if other is null
*/
public FluentIterable append(final Iterable other) {
return of(IterableUtils.chainedIterable(iterable, other));
}
/**
* Returns a new FluentIterable whose iterator will traverse the
* elements of the current and provided iterable in natural order.
*
* Example: natural ordering
*
* - this contains elements [1, 3, 5, 7]
*
- other contains elements [2, 4, 6, 8]
*
*
* The returned iterable will traverse the elements in the following
* order: [1, 2, 3, 4, 5, 6, 7, 8]
*
* @param other the other iterable to collate, may not be null
* @return a new iterable, collating this iterable with the other in natural order
* @throws NullPointerException if other is null
* @see org.apache.commons.collections4.iterators.CollatingIterator
*/
public FluentIterable collate(final Iterable other) {
return of(IterableUtils.collatedIterable(iterable, other));
}
/**
* Returns a new FluentIterable whose iterator will traverse the
* elements of the current and provided iterable according to the
* ordering defined by an comparator.
*
* Example: descending order
*
* - this contains elements [7, 5, 3, 1]
*
- other contains elements [8, 6, 4, 2]
*
*
* The returned iterable will traverse the elements in the following
* order: [8, 7, 6, 5, 4, 3, 2, 1]
*
* @param comparator the comparator to define an ordering, may be null,
* in which case natural ordering will be used
* @param other the other iterable to collate, may not be null
* @return a new iterable, collating this iterable with the other in natural order
* @throws NullPointerException if other is null
* @see org.apache.commons.collections4.iterators.CollatingIterator
*/
public FluentIterable collate(final Iterable other,
final Comparator comparator) {
return of(IterableUtils.collatedIterable(comparator, iterable, other));
}
/**
* This method fully traverses an iterator of this iterable and returns
* a new iterable with the same contents, but without any reference
* to the originating iterables and/or iterators.
*
* Calling this method is equivalent to:
*
* FluentIterable<E> someIterable = ...;
* FluentIterable.of(someIterable.toList());
*
*
* @return a new iterable with the same contents as this iterable
*/
public FluentIterable eval() {
return of(toList());
}
/**
* Returns a new FluentIterable whose iterator will only return
* elements from this iterable matching the provided predicate.
*
* @param predicate the predicate used to filter elements
* @return a new iterable, providing a filtered view of this iterable
* @throws NullPointerException if predicate is null
*/
public FluentIterable filter(final Predicate predicate) {
return of(IterableUtils.filteredIterable(iterable, predicate));
}
/**
* Returns a new FluentIterable whose iterator will return at most
* the provided maximum number of elements from this iterable.
*
* @param maxSize the maximum number of elements
* @return a new iterable, providing a bounded view of this iterable
* @throws IllegalArgumentException if maxSize is negative
*/
public FluentIterable limit(final long maxSize) {
return of(IterableUtils.boundedIterable(iterable, maxSize));
}
/**
* Returns a new FluentIterable whose iterator will loop infinitely
* over the elements from this iterable.
*
* @return a new iterable, providing a looping view of this iterable
*/
public FluentIterable loop() {
return of(IterableUtils.loopingIterable(iterable));
}
/**
* Returns a new FluentIterable whose iterator will traverse the
* elements from this iterable in reverse order.
*
* @return a new iterable, providing a reversed view of this iterable
*/
public FluentIterable reverse() {
return of(IterableUtils.reversedIterable(iterable));
}
/**
* Returns a new FluentIterable whose iterator will skip the first
* N elements from this iterable.
*
* @param elementsToSkip the number of elements to skip
* @return a new iterable, providing a view of this iterable by skipping
* the first N elements
* @throws IllegalArgumentException if elementsToSkip is negative
*/
public FluentIterable skip(final long elementsToSkip) {
return of(IterableUtils.skippingIterable(iterable, elementsToSkip));
}
/**
* Returns a new FluentIterable whose iterator will return all elements
* of this iterable transformed by the provided transformer.
*
* @param the output element type
* @param transformer the transformer applied to each element
* @return a new iterable, providing a transformed view of this iterable
* @throws NullPointerException if transformer is null
*/
public FluentIterable transform(final Transformer transformer) {
return of(IterableUtils.transformedIterable(iterable, transformer));
}
/**
* Returns a new FluentIterable whose iterator will return a unique view
* of this iterable.
*
* @return a new iterable, providing a unique view of this iterable
*/
public FluentIterable unique() {
return of(IterableUtils.uniqueIterable(iterable));
}
/**
* Returns a new FluentIterable whose iterator will return an unmodifiable
* view of this iterable.
*
* @return a new iterable, providing an unmodifiable view of this iterable
*/
public FluentIterable unmodifiable() {
return of(IterableUtils.unmodifiableIterable(iterable));
}
/**
* Returns a new FluentIterable whose iterator will traverse
* the elements of this iterable and the other iterable in
* alternating order.
*
* @param other the other iterable to interleave, may not be null
* @return a new iterable, interleaving this iterable with others
* @throws NullPointerException if other is null
*/
public FluentIterable zip(final Iterable other) {
return of(IterableUtils.zippingIterable(iterable, other));
}
/**
* Returns a new FluentIterable whose iterator will traverse
* the elements of this iterable and the other iterables in
* alternating order.
*
* @param others the iterables to interleave, may not be null
* @return a new iterable, interleaving this iterable with others
* @throws NullPointerException if either of the provided iterables is null
*/
public FluentIterable zip(final Iterable... others) {
return of(IterableUtils.zippingIterable(iterable, others));
}
// convenience methods
// ----------------------------------------------------------------------
/** {@inheritDoc} */
@Override
public Iterator iterator() {
return iterable.iterator();
}
/**
* Returns an Enumeration that will enumerate all elements contained
* in this iterable.
*
* @return an Enumeration over the elements of this iterable
*/
public Enumeration asEnumeration() {
return IteratorUtils.asEnumeration(iterator());
}
/**
* Checks if all elements contained in this iterable are matching the
* provided predicate.
*
* A null or empty iterable returns true.
*
* @param predicate the predicate to use, may not be null
* @return true if all elements contained in this iterable match the predicate,
* false otherwise
* @throws NullPointerException if predicate is null
*/
public boolean allMatch(final Predicate predicate) {
return IterableUtils.matchesAll(iterable, predicate);
}
/**
* Checks if this iterable contains any element matching the provided predicate.
*
* A null or empty iterable returns false.
*
* @param predicate the predicate to use, may not be null
* @return true if at least one element contained in this iterable matches the predicate,
* false otherwise
* @throws NullPointerException if predicate is null
*/
public boolean anyMatch(final Predicate predicate) {
return IterableUtils.matchesAny(iterable, predicate);
}
/**
* Checks if this iterable is empty.
*
* @return true if this iterable does not contain any elements, false otherwise
*/
public boolean isEmpty() {
return IterableUtils.isEmpty(iterable);
}
/**
* Checks if the object is contained in this iterable.
*
* @param object the object to check
* @return true if the object is contained in this iterable, false otherwise
*/
public boolean contains(final Object object) {
return IterableUtils.contains(iterable, object);
}
/**
* Applies the closure to all elements contained in this iterable.
*
* @param closure the closure to apply to each element, may not be null
* @throws NullPointerException if closure is null
*/
public void forEach(final Closure closure) {
IterableUtils.forEach(iterable, closure);
}
/**
* Returns the element at the provided position in this iterable.
* In order to return the element, an iterator needs to be traversed
* up to the requested position.
*
* @param position the position of the element to return
* @return the element
* @throws IndexOutOfBoundsException if the provided position is outside the
* valid range of this iterable: [0, size)
*/
public E get(final int position) {
return IterableUtils.get(iterable, position);
}
/**
* Returns the number of elements that are contained in this iterable.
* In order to determine the size, an iterator needs to be traversed.
*
* @return the size of this iterable
*/
public int size() {
return IterableUtils.size(iterable);
}
/**
* Traverses an iterator of this iterable and adds all elements
* to the provided collection.
*
* @param collection the collection to add the elements
* @throws NullPointerException if collection is null
*/
public void copyInto(final Collection collection) {
if (collection == null) {
throw new NullPointerException("Collection must not be null");
}
CollectionUtils.addAll(collection, iterable);
}
/**
* Returns an array containing all elements of this iterable by traversing
* its iterator.
*
* @param arrayClass the class of array to create
* @return an array of the iterable contents
* @throws ArrayStoreException if arrayClass is invalid
*/
public E[] toArray(final Class arrayClass) {
return IteratorUtils.toArray(iterator(), arrayClass);
}
/**
* Returns a mutable list containing all elements of this iterable
* by traversing its iterator.
*
* The returned list is guaranteed to be mutable.
*
* @return a list of the iterable contents
*/
public List toList() {
return IterableUtils.toList(iterable);
}
/** {@inheritDoc} */
@Override
public String toString() {
return IterableUtils.toString(iterable);
}
}