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org.apache.commons.collections4.IterableUtils Maven / Gradle / Ivy
The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* 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.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import org.apache.commons.collections4.functors.EqualPredicate;
import org.apache.commons.collections4.iterators.LazyIteratorChain;
import org.apache.commons.collections4.iterators.ReverseListIterator;
import org.apache.commons.collections4.iterators.UniqueFilterIterator;
/**
* Provides utility methods and decorators for {@link Iterable} instances.
*
* Note : this util class has been designed for fail-fast argument checking.
*
*
* all decorator methods are NOT null-safe wrt the provided Iterable argument, i.e.
* they will throw a {@link NullPointerException} if a null Iterable is passed as argument.
*
* all other utility methods are null-safe wrt the provided Iterable argument, i.e. they will
* treat a null Iterable the same way as an empty one. Other arguments which are null,
* e.g. a {@link Predicate}, will result in a {@link NullPointerException}. Exception: passing
* a null {@link Comparator} is equivalent to a Comparator with natural ordering.
*
*
* @since 4.1
* @version $Id: IterableUtils.java 1716538 2015-11-25 20:27:49Z tn $
*/
public class IterableUtils {
/**
* An empty iterable.
*/
@SuppressWarnings("rawtypes")
static final FluentIterable EMPTY_ITERABLE = new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.emptyIterator();
}
};
// Empty
// ----------------------------------------------------------------------
/**
* Gets an empty iterable.
*
* This iterable does not contain any elements.
*
* @param the element type
* @return an empty iterable
*/
@SuppressWarnings("unchecked") // OK, empty collection is compatible with any type
public static Iterable emptyIterable() {
return EMPTY_ITERABLE;
}
// Chained
// ----------------------------------------------------------------------
/**
* Combines two iterables into a single iterable.
*
* The returned iterable has an iterator that traverses the elements in {@code a},
* followed by the elements in {@code b}. The source iterators are not polled until
* necessary.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param a the first iterable, may not be null
* @param b the second iterable, may not be null
* @return a new iterable, combining the provided iterables
* @throws NullPointerException if either a or b is null
*/
@SuppressWarnings("unchecked")
public static Iterable chainedIterable(final Iterable a,
final Iterable b) {
return chainedIterable(new Iterable[] {a, b});
}
/**
* Combines three iterables into a single iterable.
*
* The returned iterable has an iterator that traverses the elements in {@code a},
* followed by the elements in {@code b} and {@code c}. The source iterators are
* not polled until necessary.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param a the first iterable, may not be null
* @param b the second iterable, may not be null
* @param c the third iterable, may not be null
* @return a new iterable, combining the provided iterables
* @throws NullPointerException if either of the provided iterables is null
*/
@SuppressWarnings("unchecked")
public static Iterable chainedIterable(final Iterable a,
final Iterable b,
final Iterable c) {
return chainedIterable(new Iterable[] {a, b, c});
}
/**
* Combines four iterables into a single iterable.
*
* The returned iterable has an iterator that traverses the elements in {@code a},
* followed by the elements in {@code b}, {@code c} and {@code d}. The source
* iterators are not polled until necessary.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param a the first iterable, may not be null
* @param b the second iterable, may not be null
* @param c the third iterable, may not be null
* @param d the fourth iterable, may not be null
* @return a new iterable, combining the provided iterables
* @throws NullPointerException if either of the provided iterables is null
*/
@SuppressWarnings("unchecked")
public static Iterable chainedIterable(final Iterable a,
final Iterable b,
final Iterable c,
final Iterable d) {
return chainedIterable(new Iterable[] {a, b, c, d});
}
/**
* Combines the provided iterables into a single iterable.
*
* The returned iterable has an iterator that traverses the elements in the order
* of the arguments, i.e. iterables[0], iterables[1], .... The source iterators
* are not polled until necessary.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param iterables the iterables to combine, may not be null
* @return a new iterable, combining the provided iterables
* @throws NullPointerException if either of the provided iterables is null
*/
public static Iterable chainedIterable(final Iterable... iterables) {
checkNotNull(iterables);
return new FluentIterable() {
@Override
public Iterator iterator() {
return new LazyIteratorChain() {
@Override
protected Iterator nextIterator(int count) {
if (count > iterables.length) {
return null;
} else {
return iterables[count - 1].iterator();
}
}
};
}
};
}
// Collated
// ----------------------------------------------------------------------
/**
* Combines the two provided iterables into an ordered iterable using
* natural ordering.
*
* The returned iterable's iterator supports {@code remove()} when the
* corresponding input iterator supports it.
*
* @param the element type
* @param a the first iterable, may not be null
* @param b the second iterable, may not be null
* @return a filtered view on the specified iterable
* @throws NullPointerException if either of the provided iterables is null
*/
public static Iterable collatedIterable(final Iterable a,
final Iterable b) {
checkNotNull(a, b);
return new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.collatedIterator(null, a.iterator(), b.iterator());
}
};
}
/**
* Combines the two provided iterables into an ordered iterable using the
* provided comparator. If the comparator is null, natural ordering will be
* used.
*
* The returned iterable's iterator supports {@code remove()} when the
* corresponding input iterator supports it.
*
* @param the element type
* @param comparator the comparator defining an ordering over the elements,
* may be null, in which case natural ordering will be used
* @param a the first iterable, may not be null
* @param b the second iterable, may not be null
* @return a filtered view on the specified iterable
* @throws NullPointerException if either of the provided iterables is null
*/
public static Iterable collatedIterable(final Comparator comparator,
final Iterable a,
final Iterable b) {
checkNotNull(a, b);
return new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.collatedIterator(comparator, a.iterator(), b.iterator());
}
};
}
// Filtered
// ----------------------------------------------------------------------
/**
* Returns a view of the given iterable that only contains elements matching
* the provided predicate.
*
* The returned iterable's iterator supports {@code remove()} when the
* corresponding input iterator supports it.
*
* @param the element type
* @param iterable the iterable to filter, may not be null
* @param predicate the predicate used to filter elements, may not be null
* @return a filtered view on the specified iterable
* @throws NullPointerException if either iterable or predicate is null
*/
public static Iterable filteredIterable(final Iterable iterable,
final Predicate predicate) {
checkNotNull(iterable);
if (predicate == null) {
throw new NullPointerException("Predicate must not be null.");
}
return new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.filteredIterator(emptyIteratorIfNull(iterable), predicate);
}
};
}
// Bounded
// ----------------------------------------------------------------------
/**
* Returns a view of the given iterable that contains at most the given number
* of elements.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param iterable the iterable to limit, may not be null
* @param maxSize the maximum number of elements, must not be negative
* @return a bounded view on the specified iterable
* @throws IllegalArgumentException if maxSize is negative
* @throws NullPointerException if iterable is null
*/
public static Iterable boundedIterable(final Iterable iterable, final long maxSize) {
checkNotNull(iterable);
if (maxSize < 0) {
throw new IllegalArgumentException("MaxSize parameter must not be negative.");
}
return new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.boundedIterator(iterable.iterator(), maxSize);
}
};
}
// Looping
// ----------------------------------------------------------------------
/**
* Returns a view of the given iterable which will cycle infinitely over
* its elements.
*
* The returned iterable's iterator supports {@code remove()} if
* {@code iterable.iterator()} does. After {@code remove()} is called, subsequent
* cycles omit the removed element, which is no longer in {@code iterable}. The
* iterator's {@code hasNext()} method returns {@code true} until {@code iterable}
* is empty.
*
* @param the element type
* @param iterable the iterable to loop, may not be null
* @return a view of the iterable, providing an infinite loop over its elements
* @throws NullPointerException if iterable is null
*/
public static Iterable loopingIterable(final Iterable iterable) {
checkNotNull(iterable);
return new FluentIterable() {
@Override
public Iterator iterator() {
return new LazyIteratorChain() {
@Override
protected Iterator nextIterator(int count) {
if (IterableUtils.isEmpty(iterable)) {
return null;
} else {
return iterable.iterator();
}
}
};
}
};
}
// Reversed
// ----------------------------------------------------------------------
/**
* Returns a reversed view of the given iterable.
*
* In case the provided iterable is a {@link List} instance, a
* {@link ReverseListIterator} will be used to reverse the traversal
* order, otherwise an intermediate {@link List} needs to be created.
*
* The returned iterable's iterator supports {@code remove()} if the
* provided iterable is a {@link List} instance.
*
* @param the element type
* @param iterable the iterable to use, may not be null
* @return a reversed view of the specified iterable
* @throws NullPointerException if iterable is null
* @see ReverseListIterator
*/
public static Iterable reversedIterable(final Iterable iterable) {
checkNotNull(iterable);
return new FluentIterable() {
@Override
public Iterator iterator() {
final List list = (iterable instanceof List) ?
(List) iterable :
IteratorUtils.toList(iterable.iterator());
return new ReverseListIterator(list);
}
};
}
// Skipping
// ----------------------------------------------------------------------
/**
* Returns a view of the given iterable that skips the first N elements.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param iterable the iterable to use, may not be null
* @param elementsToSkip the number of elements to skip from the start, must not be negative
* @return a view of the specified iterable, skipping the first N elements
* @throws IllegalArgumentException if elementsToSkip is negative
* @throws NullPointerException if iterable is null
*/
public static Iterable skippingIterable(final Iterable iterable, final long elementsToSkip) {
checkNotNull(iterable);
if (elementsToSkip < 0) {
throw new IllegalArgumentException("ElementsToSkip parameter must not be negative.");
}
return new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.skippingIterator(iterable.iterator(), elementsToSkip);
}
};
}
// Transformed
// ----------------------------------------------------------------------
/**
* Returns a transformed view of the given iterable where all of its elements
* have been transformed by the provided transformer.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the input element type
* @param the output element type
* @param iterable the iterable to transform, may not be null
* @param transformer the transformer, must not be null
* @return a transformed view of the specified iterable
* @throws NullPointerException if either iterable or transformer is null
*/
public static Iterable transformedIterable(final Iterable iterable,
final Transformer transformer) {
checkNotNull(iterable);
if (transformer == null) {
throw new NullPointerException("Transformer must not be null.");
}
return new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.transformedIterator(iterable.iterator(), transformer);
}
};
}
// Unique
// ----------------------------------------------------------------------
/**
* Returns a unique view of the given iterable.
*
* The returned iterable's iterator supports {@code remove()} when the
* corresponding input iterator supports it. Calling {@code remove()}
* will only remove a single element from the underlying iterator.
*
* @param the element type
* @param iterable the iterable to use, may not be null
* @return a unique view of the specified iterable
* @throws NullPointerException if iterable is null
*/
public static Iterable uniqueIterable(final Iterable iterable) {
checkNotNull(iterable);
return new FluentIterable() {
@Override
public Iterator iterator() {
return new UniqueFilterIterator(iterable.iterator());
}
};
}
// Unmodifiable
// ----------------------------------------------------------------------
/**
* Returns an unmodifiable view of the given iterable.
*
* The returned iterable's iterator does not support {@code remove()}.
*
* @param the element type
* @param iterable the iterable to use, may not be null
* @return an unmodifiable view of the specified iterable
* @throws NullPointerException if iterable is null
*/
public static Iterable unmodifiableIterable(final Iterable iterable) {
checkNotNull(iterable);
if (iterable instanceof UnmodifiableIterable) {
return iterable;
}
return new UnmodifiableIterable(iterable);
}
/**
* Inner class to distinguish unmodifiable instances.
*/
private static final class UnmodifiableIterable extends FluentIterable {
private final Iterable unmodifiable;
public UnmodifiableIterable(final Iterable iterable) {
super();
this.unmodifiable = iterable;
}
@Override
public Iterator iterator() {
return IteratorUtils.unmodifiableIterator(unmodifiable.iterator());
}
}
// Zipping
// ----------------------------------------------------------------------
/**
* Interleaves two iterables into a single iterable.
*
* The returned iterable has an iterator that traverses the elements in {@code a}
* and {@code b} in alternating order. The source iterators are not polled until
* necessary.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param a the first iterable, may not be null
* @param b the second iterable, may not be null
* @return a new iterable, interleaving the provided iterables
* @throws NullPointerException if either a or b is null
*/
public static Iterable zippingIterable(final Iterable a,
final Iterable b) {
checkNotNull(a);
checkNotNull(b);
return new FluentIterable() {
@Override
public Iterator iterator() {
return IteratorUtils.zippingIterator(a.iterator(), b.iterator());
}
};
}
/**
* Interleaves two iterables into a single iterable.
*
* The returned iterable has an iterator that traverses the elements in {@code a}
* and {@code b} in alternating order. The source iterators are not polled until
* necessary.
*
* The returned iterable's iterator supports {@code remove()} when the corresponding
* input iterator supports it.
*
* @param the element type
* @param first the first iterable, may not be null
* @param others the array of iterables to interleave, may not be null
* @return a new iterable, interleaving the provided iterables
* @throws NullPointerException if either of the provided iterables is null
*/
public static Iterable zippingIterable(final Iterable first,
final Iterable... others) {
checkNotNull(first);
checkNotNull(others);
return new FluentIterable() {
@Override
public Iterator iterator() {
@SuppressWarnings("unchecked") // safe
Iterator[] iterators = new Iterator[others.length + 1];
iterators[0] = first.iterator();
for (int i = 0; i < others.length; i++) {
iterators[i + 1] = others[i].iterator();
}
return IteratorUtils.zippingIterator(iterators);
}
};
}
// Utility methods
// ----------------------------------------------------------------------
/**
* Returns an immutable empty iterable if the argument is null,
* or the argument itself otherwise.
*
* @param the element type
* @param iterable the iterable, may be null
* @return an empty iterable if the argument is null
*/
public static Iterable emptyIfNull(final Iterable iterable) {
return iterable == null ? IterableUtils.emptyIterable() : iterable;
}
/**
* Applies the closure to each element of the provided iterable.
*
* @param the element type
* @param iterable the iterator to use, may be null
* @param closure the closure to apply to each element, may not be null
* @throws NullPointerException if closure is null
*/
public static void forEach(final Iterable iterable, final Closure closure) {
IteratorUtils.forEach(emptyIteratorIfNull(iterable), closure);
}
/**
* Executes the given closure on each but the last element in the iterable.
*
* If the input iterable is null no change is made.
*
* @param the type of object the {@link Iterable} contains
* @param iterable the iterable to get the input from, may be null
* @param closure the closure to perform, may not be null
* @return the last element in the iterable, or null if iterable is null or empty
*/
public static E forEachButLast(final Iterable iterable, final Closure closure) {
return IteratorUtils.forEachButLast(emptyIteratorIfNull(iterable), closure);
}
/**
* Finds the first element in the given iterable which matches the given predicate.
*
* A null or empty iterator returns null.
*
* @param the element type
* @param iterable the iterable to search, may be null
* @param predicate the predicate to use, may not be null
* @return the first element of the iterable which matches the predicate or null if none could be found
* @throws NullPointerException if predicate is null
*/
public static E find(final Iterable iterable, final Predicate predicate) {
return IteratorUtils.find(emptyIteratorIfNull(iterable), predicate);
}
/**
* Returns the index of the first element in the specified iterable that
* matches the given predicate.
*
* A null or empty iterable returns -1.
*
* @param the element type
* @param iterable the iterable to search, may be null
* @param predicate the predicate to use, may not be null
* @return the index of the first element which matches the predicate or -1 if none matches
* @throws NullPointerException if predicate is null
*/
public static int indexOf(final Iterable iterable, final Predicate predicate) {
return IteratorUtils.indexOf(emptyIteratorIfNull(iterable), predicate);
}
/**
* Answers true if a predicate is true for every element of an iterable.
*
* A null or empty iterable returns true.
*
* @param the type of object the {@link Iterable} contains
* @param iterable the {@link Iterable} to use, may be null
* @param predicate the predicate to use, may not be null
* @return true if every element of the collection matches the predicate or if the
* collection is empty, false otherwise
* @throws NullPointerException if predicate is null
*/
public static boolean matchesAll(final Iterable iterable, final Predicate predicate) {
return IteratorUtils.matchesAll(emptyIteratorIfNull(iterable), predicate);
}
/**
* Answers true if a predicate is true for any element of the iterable.
*
* A null or empty iterable returns false.
*
* @param the type of object the {@link Iterable} contains
* @param iterable the {@link Iterable} to use, may be null
* @param predicate the predicate to use, may not be null
* @return true if any element of the collection matches the predicate, false otherwise
* @throws NullPointerException if predicate is null
*/
public static boolean matchesAny(final Iterable iterable, final Predicate predicate) {
return IteratorUtils.matchesAny(emptyIteratorIfNull(iterable), predicate);
}
/**
* Counts the number of elements in the input iterable that match the predicate.
*
* A null iterable matches no elements.
*
* @param the type of object the {@link Iterable} contains
* @param input the {@link Iterable} to get the input from, may be null
* @param predicate the predicate to use, may not be null
* @return the number of matches for the predicate in the collection
* @throws NullPointerException if predicate is null
*/
public static long countMatches(final Iterable input, final Predicate predicate) {
if (predicate == null) {
throw new NullPointerException("Predicate must not be null.");
}
return size(filteredIterable(emptyIfNull(input), predicate));
}
/**
* Answers true if the provided iterable is empty.
*
* A null iterable returns true.
*
* @param iterable the {@link Iterable to use}, may be null
* @return true if the iterable is null or empty, false otherwise
*/
public static boolean isEmpty(final Iterable iterable) {
if (iterable instanceof Collection) {
return ((Collection) iterable).isEmpty();
} else {
return IteratorUtils.isEmpty(emptyIteratorIfNull(iterable));
}
}
/**
* Checks if the object is contained in the given iterable.
*
* A null or empty iterable returns false.
*
* @param the type of object the {@link Iterable} contains
* @param iterable the iterable to check, may be null
* @param object the object to check
* @return true if the object is contained in the iterable, false otherwise
*/
public static boolean contains(final Iterable iterable, final Object object) {
if (iterable instanceof Collection) {
return ((Collection) iterable).contains(object);
} else {
return IteratorUtils.contains(emptyIteratorIfNull(iterable), object);
}
}
/**
* Checks if the object is contained in the given iterable. Object equality
* is tested with an {@code equator} unlike {@link #contains(Iterable, Object)}
* which uses {@link Object#equals(Object)}.
*
* A null or empty iterable returns false.
* A null object will not be passed to the equator, instead a
* {@link org.apache.commons.collections4.functors.NullPredicate NullPredicate}
* will be used.
*
* @param the type of object the {@link Iterable} contains
* @param iterable the iterable to check, may be null
* @param object the object to check
* @param equator the equator to use to check, may not be null
* @return true if the object is contained in the iterable, false otherwise
* @throws NullPointerException if equator is null
*/
public static boolean contains(final Iterable iterable, final E object,
final Equator equator) {
if (equator == null) {
throw new NullPointerException("Equator must not be null.");
}
return matchesAny(iterable, EqualPredicate.equalPredicate(object, equator));
}
/**
* Returns the number of occurrences of the provided object in the iterable.
*
* @param the element type that the {@link Iterable} may contain
* @param the element type of the object to find
* @param iterable the {@link Iterable} to search
* @param obj the object to find the cardinality of
* @return the the number of occurrences of obj in iterable
*/
public static int frequency(final Iterable iterable, final T obj) {
if (iterable instanceof Set) {
return ((Set) iterable).contains(obj) ? 1 : 0;
}
if (iterable instanceof Bag) {
return ((Bag) iterable).getCount(obj);
}
return size(filteredIterable(emptyIfNull(iterable), EqualPredicate.equalPredicate(obj)));
}
/**
* Returns the index-th value in the iterable's {@link Iterator}, throwing
* IndexOutOfBoundsException if there is no such element.
*
* If the {@link Iterable} is a {@link List}, then it will use {@link List#get(int)}.
*
* @param the type of object in the {@link Iterable}.
* @param iterable the {@link Iterable} to get a value from, may be null
* @param index the index to get
* @return the object at the specified index
* @throws IndexOutOfBoundsException if the index is invalid
*/
public static T get(final Iterable iterable, final int index) {
CollectionUtils.checkIndexBounds(index);
if (iterable instanceof List) {
return ((List) iterable).get(index);
}
return IteratorUtils.get(emptyIteratorIfNull(iterable), index);
}
/**
* Returns the number of elements contained in the given iterator.
*
* A null or empty iterator returns {@code 0}.
*
* @param iterable the iterable to check, may be null
* @return the number of elements contained in the iterable
*/
public static int size(final Iterable iterable) {
if (iterable instanceof Collection) {
return ((Collection) iterable).size();
} else {
return IteratorUtils.size(emptyIteratorIfNull(iterable));
}
}
/**
* Partitions all elements from iterable into separate output collections,
* based on the evaluation of the given predicate.
*
* For each predicate, the result will contain a list holding all elements of the
* input iterable matching the predicate. The last list will hold all elements
* which didn't match any predicate:
*
* [C1, R] = partition(I, P1) with
* I = input
* P1 = first predicate
* C1 = collection of elements matching P1
* R = collection of elements rejected by all predicates
*
*
* If the input iterable is null, the same is returned as for an
* empty iterable.
*
* Example: for an input list [1, 2, 3, 4, 5] calling partition with a predicate [x < 3]
* will result in the following output: [[1, 2], [3, 4, 5]].
*
* @param the type of object the {@link Iterable} contains
* @param iterable the iterable to partition, may be null
* @param predicate the predicate to use, may not be null
* @return a list containing the output collections
* @throws NullPointerException if predicate is null
*/
public static List> partition(final Iterable iterable,
final Predicate predicate) {
if (predicate == null) {
throw new NullPointerException("Predicate must not be null.");
}
@SuppressWarnings({ "unchecked", "rawtypes" }) // safe
final Factory> factory = FactoryUtils.instantiateFactory((Class) ArrayList.class);
@SuppressWarnings("unchecked") // safe
final Predicate[] predicates = new Predicate[] { predicate };
return partition(iterable, factory, predicates);
}
/**
* Partitions all elements from iterable into separate output collections,
* based on the evaluation of the given predicates.
*
* For each predicate, the result will contain a list holding all elements of the
* input iterable matching the predicate. The last list will hold all elements
* which didn't match any predicate:
*
* [C1, C2, R] = partition(I, P1, P2) with
* I = input
* P1 = first predicate
* P2 = second predicate
* C1 = collection of elements matching P1
* C2 = collection of elements matching P2
* R = collection of elements rejected by all predicates
*
*
* Note : elements are only added to the output collection of the first matching
* predicate, determined by the order of arguments.
*
* If the input iterable is null, the same is returned as for an
* empty iterable.
*
* Example: for an input list [1, 2, 3, 4, 5] calling partition with predicates [x < 3]
* and [x < 5] will result in the following output: [[1, 2], [3, 4], [5]].
*
* @param the type of object the {@link Iterable} contains
* @param iterable the collection to get the input from, may be null
* @param predicates the predicates to use, may not be null
* @return a list containing the output collections
* @throws NullPointerException if any predicate is null
*/
public static List> partition(final Iterable iterable,
final Predicate... predicates) {
@SuppressWarnings({ "unchecked", "rawtypes" }) // safe
final Factory> factory = FactoryUtils.instantiateFactory((Class) ArrayList.class);
return partition(iterable, factory, predicates);
}
/**
* Partitions all elements from iterable into separate output collections,
* based on the evaluation of the given predicates.
*
* For each predicate, the returned list will contain a collection holding
* all elements of the input iterable matching the predicate. The last collection
* contained in the list will hold all elements which didn't match any predicate:
*
* [C1, C2, R] = partition(I, P1, P2) with
* I = input
* P1 = first predicate
* P2 = second predicate
* C1 = collection of elements matching P1
* C2 = collection of elements matching P2
* R = collection of elements rejected by all predicates
*
*
* Note : elements are only added to the output collection of the first matching
* predicate, determined by the order of arguments.
*
* If the input iterable is null, the same is returned as for an
* empty iterable.
* If no predicates have been provided, all elements of the input collection
* will be added to the rejected collection.
*
* Example: for an input list [1, 2, 3, 4, 5] calling partition with predicates [x < 3]
* and [x < 5] will result in the following output: [[1, 2], [3, 4], [5]].
*
* @param the type of object the {@link Iterable} contains
* @param the type of the output {@link Collection}
* @param iterable the collection to get the input from, may be null
* @param partitionFactory the factory used to create the output collections
* @param predicates the predicates to use, may not be null
* @return a list containing the output collections
* @throws NullPointerException if any predicate is null
*/
public static > List partition(final Iterable iterable,
final Factory partitionFactory, final Predicate... predicates) {
if (iterable == null) {
final Iterable empty = emptyIterable();
return partition(empty, partitionFactory, predicates);
}
if (predicates == null) {
throw new NullPointerException("Predicates must not be null.");
}
for (Predicate p : predicates) {
if (p == null) {
throw new NullPointerException("Predicate must not be null.");
}
}
if (predicates.length < 1) {
// return the entire input collection as a single partition
final R singlePartition = partitionFactory.create();
CollectionUtils.addAll(singlePartition, iterable);
return Collections.singletonList(singlePartition);
}
// create the empty partitions
final int numberOfPredicates = predicates.length;
final int numberOfPartitions = numberOfPredicates + 1;
final List partitions = new ArrayList(numberOfPartitions);
for (int i = 0; i < numberOfPartitions; ++i) {
partitions.add(partitionFactory.create());
}
// for each element in inputCollection:
// find the first predicate that evaluates to true.
// if there is a predicate, add the element to the corresponding partition.
// if there is no predicate, add it to the last, catch-all partition.
for (final O element : iterable) {
boolean elementAssigned = false;
for (int i = 0; i < numberOfPredicates; ++i) {
if (predicates[i].evaluate(element)) {
partitions.get(i).add(element);
elementAssigned = true;
break;
}
}
if (!elementAssigned) {
// no predicates evaluated to true
// add element to last partition
partitions.get(numberOfPredicates).add(element);
}
}
return partitions;
}
/**
* Gets a new list with the contents of the provided iterable.
*
* @param the element type
* @param iterable the iterable to use, may be null
* @return a list of the iterator contents
*/
public static List toList(final Iterable iterable) {
return IteratorUtils.toList(emptyIteratorIfNull(iterable));
}
/**
* Returns a string representation of the elements of the specified iterable.
*
* The string representation consists of a list of the iterable's elements,
* enclosed in square brackets ({@code "[]"}). Adjacent elements are separated
* by the characters {@code ", "} (a comma followed by a space). Elements are
* converted to strings as by {@code String.valueOf(Object)}.
*
* @param the element type
* @param iterable the iterable to convert to a string, may be null
* @return a string representation of {@code iterable}
*/
public static String toString(final Iterable iterable) {
return IteratorUtils.toString(emptyIteratorIfNull(iterable));
}
/**
* Returns a string representation of the elements of the specified iterable.
*
* The string representation consists of a list of the iterable's elements,
* enclosed in square brackets ({@code "[]"}). Adjacent elements are separated
* by the characters {@code ", "} (a comma followed by a space). Elements are
* converted to strings as by using the provided {@code transformer}.
*
* @param the element type
* @param iterable the iterable to convert to a string, may be null
* @param transformer the transformer used to get a string representation of an element
* @return a string representation of {@code iterable}
* @throws NullPointerException if {@code transformer} is null
*/
public static String toString(final Iterable iterable,
final Transformer transformer) {
if (transformer == null) {
throw new NullPointerException("Transformer must not be null.");
}
return IteratorUtils.toString(emptyIteratorIfNull(iterable), transformer);
}
/**
* Returns a string representation of the elements of the specified iterable.
*
* The string representation consists of a list of the iterable's elements,
* enclosed by the provided {@code prefix} and {@code suffix}. Adjacent elements
* are separated by the provided {@code delimiter}. Elements are converted to
* strings as by using the provided {@code transformer}.
*
* @param the element type
* @param iterable the iterable to convert to a string, may be null
* @param transformer the transformer used to get a string representation of an element
* @param delimiter the string to delimit elements
* @param prefix the prefix, prepended to the string representation
* @param suffix the suffix, appended to the string representation
* @return a string representation of {@code iterable}
* @throws NullPointerException if either transformer, delimiter, prefix or suffix is null
*/
public static String toString(final Iterable iterable,
final Transformer transformer,
final String delimiter,
final String prefix,
final String suffix) {
return IteratorUtils.toString(emptyIteratorIfNull(iterable),
transformer, delimiter, prefix, suffix);
}
// Helper methods
// ----------------------------------------------------------------------
/**
* Fail-fast check for null arguments.
*
* @param iterable the iterable to check
* @throws NullPointerException if iterable is null
*/
static void checkNotNull(final Iterable iterable) {
if (iterable == null) {
throw new NullPointerException("Iterable must not be null.");
}
}
/**
* Fail-fast check for null arguments.
*
* @param iterable the iterable to check
* @throws NullPointerException if the argument or any of its contents is null
*/
static void checkNotNull(final Iterable... iterables) {
if (iterables == null) {
throw new NullPointerException("Iterables must not be null.");
}
for (final Iterable iterable : iterables) {
checkNotNull(iterable);
}
}
/**
* Returns an empty iterator if the argument is null,
* or {@code iterable.iterator()} otherwise.
*
* @param the element type
* @param iterable the iterable, possibly null
* @return an empty iterator if the argument is null
*/
private static Iterator emptyIteratorIfNull(final Iterable iterable) {
return iterable != null ? iterable.iterator() : IteratorUtils.emptyIterator();
}
}
