com.google.common.collect.Multisets Maven / Gradle / Ivy
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/*
* Copyright (C) 2007 Google Inc.
*
* Licensed 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 com.google.common.collect;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.Nullable;
/**
* Provides static utility methods for creating and working with {@link
* Multiset} instances.
*
* @author Kevin Bourrillion
* @author Mike Bostock
* @since 2 (imported from Google Collections Library)
*/
@GwtCompatible
public final class Multisets {
private Multisets() {}
/**
* Returns an unmodifiable view of the specified multiset. Query operations on
* the returned multiset "read through" to the specified multiset, and
* attempts to modify the returned multiset result in an
* {@link UnsupportedOperationException}.
*
* The returned multiset will be serializable if the specified multiset is
* serializable.
*
* @param multiset the multiset for which an unmodifiable view is to be
* generated
* @return an unmodifiable view of the multiset
*/
public static Multiset unmodifiableMultiset(
Multiset multiset) {
return new UnmodifiableMultiset(checkNotNull(multiset));
}
private static class UnmodifiableMultiset
extends ForwardingMultiset implements Serializable {
final Multiset delegate;
UnmodifiableMultiset(Multiset delegate) {
this.delegate = delegate;
}
@SuppressWarnings("unchecked")
@Override protected Multiset delegate() {
// This is safe because all non-covariant methods are overriden
return (Multiset) delegate;
}
transient Set elementSet;
@Override public Set elementSet() {
Set es = elementSet;
return (es == null)
? elementSet = Collections.unmodifiableSet(delegate.elementSet())
: es;
}
transient Set> entrySet;
@SuppressWarnings("unchecked")
@Override public Set> entrySet() {
Set> es = entrySet;
return (es == null)
// Safe because the returned set is made unmodifiable and Entry
// itself is readonly
? entrySet = (Set) Collections.unmodifiableSet(delegate.entrySet())
: es;
}
@SuppressWarnings("unchecked")
@Override public Iterator iterator() {
// Safe because the returned Iterator is made unmodifiable
return (Iterator) Iterators.unmodifiableIterator(delegate.iterator());
}
@Override public boolean add(E element) {
throw new UnsupportedOperationException();
}
@Override public int add(E element, int occurences) {
throw new UnsupportedOperationException();
}
@Override public boolean addAll(Collection elementsToAdd) {
throw new UnsupportedOperationException();
}
@Override public boolean remove(Object element) {
throw new UnsupportedOperationException();
}
@Override public int remove(Object element, int occurrences) {
throw new UnsupportedOperationException();
}
@Override public boolean removeAll(Collection elementsToRemove) {
throw new UnsupportedOperationException();
}
@Override public boolean retainAll(Collection elementsToRetain) {
throw new UnsupportedOperationException();
}
@Override public void clear() {
throw new UnsupportedOperationException();
}
@Override public int setCount(E element, int count) {
throw new UnsupportedOperationException();
}
@Override public boolean setCount(E element, int oldCount, int newCount) {
throw new UnsupportedOperationException();
}
private static final long serialVersionUID = 0;
}
/**
* Returns an immutable multiset entry with the specified element and count.
*
* @param e the element to be associated with the returned entry
* @param n the count to be associated with the returned entry
* @throws IllegalArgumentException if {@code n} is negative
*/
public static Multiset.Entry immutableEntry(
@Nullable final E e, final int n) {
checkArgument(n >= 0);
return new AbstractEntry() {
public E getElement() {
return e;
}
public int getCount() {
return n;
}
};
}
/**
* Returns a multiset view of the specified set. The multiset is backed by the
* set, so changes to the set are reflected in the multiset, and vice versa.
* If the set is modified while an iteration over the multiset is in progress
* (except through the iterator's own {@code remove} operation) the results of
* the iteration are undefined.
*
* The multiset supports element removal, which removes the corresponding
* element from the set. It does not support the {@code add} or {@code addAll}
* operations, nor does it support the use of {@code setCount} to add
* elements.
*
*
The returned multiset will be serializable if the specified set is
* serializable. The multiset is threadsafe if the set is threadsafe.
*
* @param set the backing set for the returned multiset view
*/
static Multiset forSet(Set set) {
return new SetMultiset(set);
}
/** @see Multisets#forSet */
private static class SetMultiset extends ForwardingCollection
implements Multiset, Serializable {
final Set delegate;
SetMultiset(Set set) {
delegate = checkNotNull(set);
}
@Override protected Set delegate() {
return delegate;
}
public int count(Object element) {
return delegate.contains(element) ? 1 : 0;
}
public int add(E element, int occurrences) {
throw new UnsupportedOperationException();
}
public int remove(Object element, int occurrences) {
if (occurrences == 0) {
return count(element);
}
checkArgument(occurrences > 0);
return delegate.remove(element) ? 1 : 0;
}
transient Set elementSet;
public Set elementSet() {
Set es = elementSet;
return (es == null) ? elementSet = new ElementSet() : es;
}
transient Set> entrySet;
public Set> entrySet() {
Set> es = entrySet;
return (es == null) ? entrySet = new EntrySet() : es;
}
@Override public boolean add(E o) {
throw new UnsupportedOperationException();
}
@Override public boolean addAll(Collection c) {
throw new UnsupportedOperationException();
}
public int setCount(E element, int count) {
checkNonnegative(count, "count");
if (count == count(element)) {
return count;
} else if (count == 0) {
remove(element);
return 1;
} else {
throw new UnsupportedOperationException();
}
}
public boolean setCount(E element, int oldCount, int newCount) {
return setCountImpl(this, element, oldCount, newCount);
}
@Override public boolean equals(@Nullable Object object) {
if (object instanceof Multiset) {
Multiset that = (Multiset) object;
return this.size() == that.size() && delegate.equals(that.elementSet());
}
return false;
}
@Override public int hashCode() {
int sum = 0;
for (E e : this) {
sum += ((e == null) ? 0 : e.hashCode()) ^ 1;
}
return sum;
}
/** @see SetMultiset#elementSet */
class ElementSet extends ForwardingSet {
@Override protected Set delegate() {
return delegate;
}
@Override public boolean add(E o) {
throw new UnsupportedOperationException();
}
@Override public boolean addAll(Collection c) {
throw new UnsupportedOperationException();
}
}
/** @see SetMultiset#entrySet */
class EntrySet extends AbstractSet> {
@Override public int size() {
return delegate.size();
}
@Override public Iterator> iterator() {
return new Iterator>() {
final Iterator elements = delegate.iterator();
public boolean hasNext() {
return elements.hasNext();
}
public Entry next() {
return immutableEntry(elements.next(), 1);
}
public void remove() {
elements.remove();
}
};
}
// TODO: faster contains, remove
}
private static final long serialVersionUID = 0;
}
/**
* Returns the expected number of distinct elements given the specified
* elements. The number of distinct elements is only computed if {@code
* elements} is an instance of {@code Multiset}; otherwise the default value
* of 11 is returned.
*/
static int inferDistinctElements(Iterable elements) {
if (elements instanceof Multiset) {
return ((Multiset) elements).elementSet().size();
}
return 11; // initial capacity will be rounded up to 16
}
/**
* Returns an unmodifiable view of the intersection of two multisets.
* An element's count in the multiset is the smaller of its counts in the two
* backing multisets. The iteration order of the returned multiset matches the
* element set of {@code multiset1}, with repeated occurrences of the same
* element appearing consecutively.
*
* Results are undefined if {@code multiset1} and {@code multiset2} are
* based on different equivalence relations (as {@code HashMultiset} and
* {@code TreeMultiset} are).
*
* @since 2
*/
public static Multiset intersection(
final Multiset multiset1, final Multiset multiset2) {
checkNotNull(multiset1);
checkNotNull(multiset2);
return new AbstractMultiset() {
@Override public int count(Object element) {
int count1 = multiset1.count(element);
return (count1 == 0) ? 0 : Math.min(count1, multiset2.count(element));
}
@Override Set createElementSet() {
return Sets.intersection(
multiset1.elementSet(), multiset2.elementSet());
}
@Override public Set> entrySet() {
return entrySet;
}
final Set> entrySet = new AbstractSet>() {
@Override public Iterator> iterator() {
final Iterator> iterator1 = multiset1.entrySet().iterator();
return new AbstractIterator>() {
@Override protected Entry computeNext() {
while (iterator1.hasNext()) {
Entry entry1 = iterator1.next();
E element = entry1.getElement();
int count
= Math.min(entry1.getCount(), multiset2.count(element));
if (count > 0) {
return Multisets.immutableEntry(element, count);
}
}
return endOfData();
}
};
}
@Override public int size() {
return elementSet().size();
}
@Override public boolean contains(Object o) {
if (o instanceof Entry) {
Entry entry = (Entry) o;
int entryCount = entry.getCount();
return (entryCount > 0)
&& (count(entry.getElement()) == entryCount);
}
return false;
}
@Override public boolean isEmpty() {
return elementSet().isEmpty();
}
};
};
}
/**
* Implementation of the {@code equals}, {@code hashCode}, and
* {@code toString} methods of {@link Multiset.Entry}.
*/
abstract static class AbstractEntry implements Multiset.Entry {
/**
* Indicates whether an object equals this entry, following the behavior
* specified in {@link Multiset.Entry#equals}.
*/
@Override public boolean equals(@Nullable Object object) {
if (object instanceof Multiset.Entry) {
Multiset.Entry that = (Multiset.Entry) object;
return this.getCount() == that.getCount()
&& Objects.equal(this.getElement(), that.getElement());
}
return false;
}
/**
* Return this entry's hash code, following the behavior specified in
* {@link Multiset.Entry#hashCode}.
*/
@Override public int hashCode() {
E e = getElement();
return ((e == null) ? 0 : e.hashCode()) ^ getCount();
}
/**
* Returns a string representation of this multiset entry. The string
* representation consists of the associated element if the associated count
* is one, and otherwise the associated element followed by the characters
* " x " (space, x and space) followed by the count. Elements and counts are
* converted to strings as by {@code String.valueOf}.
*/
@Override public String toString() {
String text = String.valueOf(getElement());
int n = getCount();
return (n == 1) ? text : (text + " x " + n);
}
}
static int setCountImpl(Multiset self, E element, int count) {
checkNonnegative(count, "count");
int oldCount = self.count(element);
int delta = count - oldCount;
if (delta > 0) {
self.add(element, delta);
} else if (delta < 0) {
self.remove(element, -delta);
}
return oldCount;
}
static boolean setCountImpl(
Multiset self, E element, int oldCount, int newCount) {
checkNonnegative(oldCount, "oldCount");
checkNonnegative(newCount, "newCount");
if (self.count(element) == oldCount) {
self.setCount(element, newCount);
return true;
} else {
return false;
}
}
static void checkNonnegative(int count, String name) {
checkArgument(count >= 0, "%s cannot be negative: %s", name, count);
}
}