/*
* 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.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.NavigableSet;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import org.apache.commons.collections4.set.ListOrderedSet;
import org.apache.commons.collections4.set.PredicatedNavigableSet;
import org.apache.commons.collections4.set.PredicatedSet;
import org.apache.commons.collections4.set.PredicatedSortedSet;
import org.apache.commons.collections4.set.TransformedNavigableSet;
import org.apache.commons.collections4.set.TransformedSet;
import org.apache.commons.collections4.set.TransformedSortedSet;
import org.apache.commons.collections4.set.UnmodifiableNavigableSet;
import org.apache.commons.collections4.set.UnmodifiableSet;
import org.apache.commons.collections4.set.UnmodifiableSortedSet;
/**
* Provides utility methods and decorators for
* {@link Set} and {@link SortedSet} instances.
*
* @since 2.1
* @version $Id$
*/
public class SetUtils {
/**
* Get a typed empty unmodifiable Set.
* @param <E> the element type
* @return an empty Set
*/
public static <E> Set<E> emptySet() {
return Collections.<E>emptySet();
}
/**
* An empty unmodifiable sorted set.
* This is not provided in the JDK.
*/
@SuppressWarnings("rawtypes")
public static final SortedSet EMPTY_SORTED_SET =
UnmodifiableSortedSet.unmodifiableSortedSet(new TreeSet<Object>());
/**
* Get a typed empty unmodifiable sorted set.
* @param <E> the element type
* @return an empty sorted Set
*/
@SuppressWarnings("unchecked") // empty set is OK for any type
public static <E> SortedSet<E> emptySortedSet() {
return EMPTY_SORTED_SET;
}
/**
* <code>SetUtils</code> should not normally be instantiated.
*/
private SetUtils() {}
//-----------------------------------------------------------------------
/**
* Returns an immutable empty set if the argument is <code>null</code>,
* or the argument itself otherwise.
*
* @param <T> the element type
* @param set the set, possibly <code>null</code>
* @return an empty set if the argument is <code>null</code>
*/
public static <T> Set<T> emptyIfNull(final Set<T> set) {
return set == null ? Collections.<T>emptySet() : set;
}
/**
* Tests two sets for equality as per the <code>equals()</code> contract
* in {@link java.util.Set#equals(java.lang.Object)}.
* <p>
* This method is useful for implementing <code>Set</code> when you cannot
* extend AbstractSet. The method takes Collection instances to enable other
* collection types to use the Set implementation algorithm.
* <p>
* The relevant text (slightly paraphrased as this is a static method) is:
* <blockquote>
* <p>Two sets are considered equal if they have
* the same size, and every member of the first set is contained in
* the second. This ensures that the {@code equals} method works
* properly across different implementations of the {@code Set}
* interface.</p>
*
* <p>
* This implementation first checks if the two sets are the same object:
* if so it returns {@code true}. Then, it checks if the two sets are
* identical in size; if not, it returns false. If so, it returns
* {@code a.containsAll((Collection) b)}.</p>
* </blockquote>
*
* @see java.util.Set
* @param set1 the first set, may be null
* @param set2 the second set, may be null
* @return whether the sets are equal by value comparison
*/
public static boolean isEqualSet(final Collection<?> set1, final Collection<?> set2) {
if (set1 == set2) {
return true;
}
if (set1 == null || set2 == null || set1.size() != set2.size()) {
return false;
}
return set1.containsAll(set2);
}
/**
* Generates a hash code using the algorithm specified in
* {@link java.util.Set#hashCode()}.
* <p>
* This method is useful for implementing <code>Set</code> when you cannot
* extend AbstractSet. The method takes Collection instances to enable other
* collection types to use the Set implementation algorithm.
*
* @param <T> the element type
* @see java.util.Set#hashCode()
* @param set the set to calculate the hash code for, may be null
* @return the hash code
*/
public static <T> int hashCodeForSet(final Collection<T> set) {
if (set == null) {
return 0;
}
int hashCode = 0;
for (final T obj : set) {
if (obj != null) {
hashCode += obj.hashCode();
}
}
return hashCode;
}
/**
* Returns a new hash set that matches elements based on <code>==</code> not
* <code>equals()</code>.
* <p>
* <strong>This set will violate the detail of various Set contracts.</note>
* As a general rule, don't compare this set to other sets. In particular, you can't
* use decorators like {@link ListOrderedSet} on it, which silently assume that these
* contracts are fulfilled.</strong>
* <p>
* <strong>Note that the returned set is not synchronized and is not thread-safe.</strong>
* If you wish to use this set from multiple threads concurrently, you must use
* appropriate synchronization. The simplest approach is to wrap this map
* using {@link java.util.Collections#synchronizedSet(Set)}. This class may throw
* exceptions when accessed by concurrent threads without synchronization.
*
* @param <E> the element type
* @return a new identity hash set
* @since 4.1
*/
public static <E> Set<E> newIdentityHashSet() {
return Collections.newSetFromMap(new IdentityHashMap<E, Boolean>());
}
// Set
//-----------------------------------------------------------------------
/**
* Returns a synchronized set backed by the given set.
* <p>
* You must manually synchronize on the returned set's iterator to
* avoid non-deterministic behavior:
*
* <pre>
* Set s = SetUtils.synchronizedSet(mySet);
* synchronized (s) {
* Iterator i = s.iterator();
* while (i.hasNext()) {
* process (i.next());
* }
* }
* </pre>
*
* This method is just a wrapper for {@link Collections#synchronizedSet(Set)}.
*
* @param <E> the element type
* @param set the set to synchronize, must not be null
* @return a synchronized set backed by the given set
* @throws NullPointerException if the set is null
*/
public static <E> Set<E> synchronizedSet(final Set<E> set) {
return Collections.synchronizedSet(set);
}
/**
* Returns an unmodifiable set backed by the given set.
* <p>
* This method uses the implementation in the decorators subpackage.
*
* @param <E> the element type
* @param set the set to make unmodifiable, must not be null
* @return an unmodifiable set backed by the given set
* @throws NullPointerException if the set is null
*/
public static <E> Set<E> unmodifiableSet(final Set<? extends E> set) {
return UnmodifiableSet.unmodifiableSet(set);
}
/**
* Returns a predicated (validating) set backed by the given set.
* <p>
* Only objects that pass the test in the given predicate can be added to the set.
* Trying to add an invalid object results in an IllegalArgumentException.
* It is important not to use the original set after invoking this method,
* as it is a backdoor for adding invalid objects.
*
* @param <E> the element type
* @param set the set to predicate, must not be null
* @param predicate the predicate for the set, must not be null
* @return a predicated set backed by the given set
* @throws NullPointerException if the set or predicate is null
*/
public static <E> Set<E> predicatedSet(final Set<E> set, final Predicate<? super E> predicate) {
return PredicatedSet.predicatedSet(set, predicate);
}
/**
* Returns a transformed set backed by the given set.
* <p>
* Each object is passed through the transformer as it is added to the
* Set. It is important not to use the original set after invoking this
* method, as it is a backdoor for adding untransformed objects.
* <p>
* Existing entries in the specified set will not be transformed.
* If you want that behaviour, see {@link TransformedSet#transformedSet}.
*
* @param <E> the element type
* @param set the set to transform, must not be null
* @param transformer the transformer for the set, must not be null
* @return a transformed set backed by the given set
* @throws NullPointerException if the set or transformer is null
*/
public static <E> Set<E> transformedSet(final Set<E> set,
final Transformer<? super E, ? extends E> transformer) {
return TransformedSet.transformingSet(set, transformer);
}
/**
* Returns a set that maintains the order of elements that are added
* backed by the given set.
* <p>
* If an element is added twice, the order is determined by the first add.
* The order is observed through the iterator or toArray.
*
* @param <E> the element type
* @param set the set to order, must not be null
* @return an ordered set backed by the given set
* @throws NullPointerException if the set is null
*/
public static <E> Set<E> orderedSet(final Set<E> set) {
return ListOrderedSet.listOrderedSet(set);
}
// SortedSet
//-----------------------------------------------------------------------
/**
* Returns a synchronized sorted set backed by the given sorted set.
* <p>
* You must manually synchronize on the returned set's iterator to
* avoid non-deterministic behavior:
*
* <pre>
* Set s = SetUtils.synchronizedSortedSet(mySet);
* synchronized (s) {
* Iterator i = s.iterator();
* while (i.hasNext()) {
* process (i.next());
* }
* }
* </pre>
*
* This method is just a wrapper for {@link Collections#synchronizedSortedSet(SortedSet)}.
*
* @param <E> the element type
* @param set the sorted set to synchronize, must not be null
* @return a synchronized set backed by the given set
* @throws NullPointerException if the set is null
*/
public static <E> SortedSet<E> synchronizedSortedSet(final SortedSet<E> set) {
return Collections.synchronizedSortedSet(set);
}
/**
* Returns an unmodifiable sorted set backed by the given sorted set.
* <p>
* This method uses the implementation in the decorators subpackage.
*
* @param <E> the element type
* @param set the sorted set to make unmodifiable, must not be null
* @return an unmodifiable set backed by the given set
* @throws NullPointerException if the set is null
*/
public static <E> SortedSet<E> unmodifiableSortedSet(final SortedSet<E> set) {
return UnmodifiableSortedSet.unmodifiableSortedSet(set);
}
/**
* Returns a predicated (validating) sorted set backed by the given sorted set.
* <p>
* Only objects that pass the test in the given predicate can be added to the set.
* Trying to add an invalid object results in an IllegalArgumentException.
* It is important not to use the original set after invoking this method,
* as it is a backdoor for adding invalid objects.
*
* @param <E> the element type
* @param set the sorted set to predicate, must not be null
* @param predicate the predicate for the sorted set, must not be null
* @return a predicated sorted set backed by the given sorted set
* @throws NullPointerException if the set or predicate is null
*/
public static <E> SortedSet<E> predicatedSortedSet(final SortedSet<E> set,
final Predicate<? super E> predicate) {
return PredicatedSortedSet.predicatedSortedSet(set, predicate);
}
/**
* Returns a transformed sorted set backed by the given set.
* <p>
* Each object is passed through the transformer as it is added to the
* Set. It is important not to use the original set after invoking this
* method, as it is a backdoor for adding untransformed objects.
* <p>
* Existing entries in the specified set will not be transformed.
* If you want that behaviour, see {@link TransformedSortedSet#transformedSortedSet}.
*
* @param <E> the element type
* @param set the set to transform, must not be null
* @param transformer the transformer for the set, must not be null
* @return a transformed set backed by the given set
* @throws NullPointerException if the set or transformer is null
*/
public static <E> SortedSet<E> transformedSortedSet(final SortedSet<E> set,
final Transformer<? super E, ? extends E> transformer) {
return TransformedSortedSet.transformingSortedSet(set, transformer);
}
// NavigableSet
//-----------------------------------------------------------------------
/**
* Returns an unmodifiable navigable set backed by the given navigable set.
* <p>
* This method uses the implementation in the decorators subpackage.
*
* @param <E> the element type
* @param set the navigable set to make unmodifiable, must not be null
* @return an unmodifiable set backed by the given set
* @throws NullPointerException if the set is null
* @since 4.1
*/
public static <E> SortedSet<E> unmodifiableNavigableSet(final NavigableSet<E> set) {
return UnmodifiableNavigableSet.unmodifiableNavigableSet(set);
}
/**
* Returns a predicated (validating) navigable set backed by the given navigable set.
* <p>
* Only objects that pass the test in the given predicate can be added to the set.
* Trying to add an invalid object results in an IllegalArgumentException.
* It is important not to use the original set after invoking this method,
* as it is a backdoor for adding invalid objects.
*
* @param <E> the element type
* @param set the navigable set to predicate, must not be null
* @param predicate the predicate for the navigable set, must not be null
* @return a predicated navigable set backed by the given navigable set
* @throws NullPointerException if the set or predicate is null
* @since 4.1
*/
public static <E> SortedSet<E> predicatedNavigableSet(final NavigableSet<E> set,
final Predicate<? super E> predicate) {
return PredicatedNavigableSet.predicatedNavigableSet(set, predicate);
}
/**
* Returns a transformed navigable set backed by the given navigable set.
* <p>
* Each object is passed through the transformer as it is added to the
* Set. It is important not to use the original set after invoking this
* method, as it is a backdoor for adding untransformed objects.
* <p>
* Existing entries in the specified set will not be transformed.
* If you want that behaviour, see {@link TransformedNavigableSet#transformedNavigableSet}.
*
* @param <E> the element type
* @param set the navigable set to transform, must not be null
* @param transformer the transformer for the set, must not be null
* @return a transformed set backed by the given set
* @throws NullPointerException if the set or transformer is null
* @since 4.1
*/
public static <E> SortedSet<E> transformedNavigableSet(final NavigableSet<E> set,
final Transformer<? super E, ? extends E> transformer) {
return TransformedNavigableSet.transformingNavigableSet(set, transformer);
}
// Set operations
//-----------------------------------------------------------------------
/**
* Returns a unmodifiable <b>view</b> of the union of the given {@link Set}s.
* <p>
* The returned view contains all elements of {@code a} and {@code b}.
*
* @param <E> the generic type that is able to represent the types contained
* in both input sets.
* @param a the first set, must not be null
* @param b the second set, must not be null
* @return a view of the union of the two set
* @throws NullPointerException if either input set is null
* @since 4.1
*/
public static <E> SetView<E> union(final Set<? extends E> a, final Set<? extends E> b) {
if (a == null || b == null) {
throw new NullPointerException("Sets must not be null.");
}
final SetView<E> bMinusA = difference(b, a);
return new SetView<E>() {
@Override
public boolean contains(Object o) {
return a.contains(o) || b.contains(o);
}
@Override
public Iterator<E> createIterator() {
return IteratorUtils.chainedIterator(a.iterator(), bMinusA.iterator());
}
@Override
public boolean isEmpty() {
return a.isEmpty() && b.isEmpty();
}
@Override
public int size() {
return a.size() + bMinusA.size();
}
};
}
/**
* Returns a unmodifiable <b>view</b> containing the difference of the given
* {@link Set}s, denoted by {@code a \ b} (or {@code a - b}).
* <p>
* The returned view contains all elements of {@code a} that are not a member
* of {@code b}.
*
* @param <E> the generic type that is able to represent the types contained
* in both input sets.
* @param a the set to subtract from, must not be null
* @param b the set to subtract, must not be null
* @return a view of the relative complement of of the two sets
* @since 4.1
*/
public static <E> SetView<E> difference(final Set<? extends E> a, final Set<? extends E> b) {
if (a == null || b == null) {
throw new NullPointerException("Sets must not be null.");
}
final Predicate<E> notContainedInB = new Predicate<E>() {
@Override
public boolean evaluate(E object) {
return !b.contains(object);
}
};
return new SetView<E>() {
@Override
public boolean contains(Object o) {
return a.contains(o) && !b.contains(o);
}
@Override
public Iterator<E> createIterator() {
return IteratorUtils.filteredIterator(a.iterator(), notContainedInB);
}
};
}
/**
* Returns a unmodifiable <b>view</b> of the intersection of the given {@link Set}s.
* <p>
* The returned view contains all elements that are members of both input sets
* ({@code a} and {@code b}).
*
* @param <E> the generic type that is able to represent the types contained
* in both input sets.
* @param a the first set, must not be null
* @param b the second set, must not be null
* @return a view of the intersection of the two sets
* @since 4.1
*/
public static <E> SetView<E> intersection(final Set<? extends E> a, final Set<? extends E> b) {
if (a == null || b == null) {
throw new NullPointerException("Sets must not be null.");
}
final Predicate<E> containedInB = new Predicate<E>() {
@Override
public boolean evaluate(E object) {
return b.contains(object);
}
};
return new SetView<E>() {
@Override
public boolean contains(Object o) {
return a.contains(o) && b.contains(o);
}
@Override
public Iterator<E> createIterator() {
return IteratorUtils.filteredIterator(a.iterator(), containedInB);
}
};
}
/**
* Returns a unmodifiable <b>view</b> of the symmetric difference of the given
* {@link Set}s.
* <p>
* The returned view contains all elements of {@code a} and {@code b} that are
* not a member of the other set.
* <p>
* This is equivalent to {@code union(difference(a, b), difference(b, a))}.
*
* @param <E> the generic type that is able to represent the types contained
* in both input sets.
* @param a the first set, must not be null
* @param b the second set, must not be null
* @return a view of the symmetric difference of the two sets
* @since 4.1
*/
public static <E> SetView<E> disjunction(final Set<? extends E> a, final Set<? extends E> b) {
if (a == null || b == null) {
throw new NullPointerException("Sets must not be null.");
}
final SetView<E> aMinusB = difference(a, b);
final SetView<E> bMinusA = difference(b, a);
return new SetView<E>() {
@Override
public boolean contains(Object o) {
return a.contains(o) ^ b.contains(o);
}
@Override
public Iterator<E> createIterator() {
return IteratorUtils.chainedIterator(aMinusB.iterator(), bMinusA.iterator());
}
@Override
public boolean isEmpty() {
return aMinusB.isEmpty() && bMinusA.isEmpty();
}
@Override
public int size() {
return aMinusB.size() + bMinusA.size();
}
};
}
/**
* An unmodifiable <b>view</b> of a set that may be backed by other sets.
* <p>
* If the decorated sets change, this view will change as well. The contents
* of this view can be transferred to another instance via the {@link #copyInto(Set)}
* and {@link #toSet()} methods.
*
* @param <E> the element type
* @since 4.1
*/
public static abstract class SetView<E> extends AbstractSet<E> {
@Override
public Iterator<E> iterator() {
return IteratorUtils.unmodifiableIterator(createIterator());
}
/**
* Return an iterator for this view; the returned iterator is
* not required to be unmodifiable.
* @return a new iterator for this view
*/
protected abstract Iterator<E> createIterator();
@Override
public int size() {
return IteratorUtils.size(iterator());
}
/**
* Copies the contents of this view into the provided set.
*
* @param <S> the set type
* @param set the set for copying the contents
*/
public <S extends Set<E>> void copyInto(final S set) {
CollectionUtils.addAll(set, this);
}
/**
* Returns a new set containing the contents of this view.
*
* @return a new set containing all elements of this view
*/
public Set<E> toSet() {
final Set<E> set = new HashSet<E>(size());
copyInto(set);
return set;
}
}
}