/*
* Copyright (C) 2007 The Guava Authors
*
* 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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.CollectPreconditions.checkRemove;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.primitives.Ints;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.InvalidObjectException;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.Nullable;
/**
* Basic implementation of {@code Multiset<E>} backed by an instance of {@code
* AbstractObjectCountMap<E>}.
*
* <p>For serialization to work, the subclass must specify explicit {@code readObject} and {@code
* writeObject} methods.
*
* @author Kevin Bourrillion
*/
@GwtCompatible(emulated = true)
abstract class AbstractMapBasedMultiset<E> extends AbstractMultiset<E> implements Serializable {
transient AbstractObjectCountMap<E> backingMap;
/*
* Cache the size for efficiency. Using a long lets us avoid the need for
* overflow checking and ensures that size() will function correctly even if
* the multiset had once been larger than Integer.MAX_VALUE.
*/
private transient long size;
/** Standard constructor. */
protected AbstractMapBasedMultiset(AbstractObjectCountMap<E> backingMap) {
this.backingMap = checkNotNull(backingMap);
this.size = super.size();
}
/** Used during deserialization only. The backing map must be empty. */
void setBackingMap(AbstractObjectCountMap<E> backingMap) {
this.backingMap = backingMap;
}
// Required Implementations
@Override
Set<E> createElementSet() {
return backingMap.keySet();
}
/**
* {@inheritDoc}
*
* <p>Invoking {@link Multiset.Entry#getCount} on an entry in the returned set always returns the
* current count of that element in the multiset, as opposed to the count at the time the entry
* was retrieved.
*/
@Override
public Set<Multiset.Entry<E>> createEntrySet() {
return new EntrySet();
}
@Override
Iterator<Entry<E>> entryIterator() {
final Iterator<Entry<E>> backingEntries = backingMap.entrySet().iterator();
return new Iterator<Multiset.Entry<E>>() {
Entry<E> toRemove;
boolean canRemove;
@Override
public boolean hasNext() {
return backingEntries.hasNext();
}
@Override
public Multiset.Entry<E> next() {
final Entry<E> mapEntry = backingEntries.next();
toRemove = mapEntry;
canRemove = true;
return mapEntry;
}
@Override
public void remove() {
checkRemove(canRemove);
size -= toRemove.getCount();
backingEntries.remove();
canRemove = false;
toRemove = null;
}
};
}
@Override
public void clear() {
backingMap.clear();
size = 0L;
}
@Override
int distinctElements() {
return backingMap.size();
}
// Optimizations - Query Operations
@Override
public int size() {
return Ints.saturatedCast(size);
}
@Override
public Iterator<E> iterator() {
return new MapBasedMultisetIterator();
}
/*
* Not subclassing AbstractMultiset$MultisetIterator because next() needs to
* retrieve the Map.Entry<E, Count> entry, which can then be used for
* a more efficient remove() call.
*/
private class MapBasedMultisetIterator implements Iterator<E> {
final Iterator<Entry<E>> entryIterator;
Entry<E> currentEntry;
int occurrencesLeft = 0;
boolean canRemove = false;
MapBasedMultisetIterator() {
this.entryIterator = backingMap.entrySet().iterator();
}
@Override
public boolean hasNext() {
return occurrencesLeft > 0 || entryIterator.hasNext();
}
@Override
public E next() {
if (occurrencesLeft == 0) {
currentEntry = entryIterator.next();
occurrencesLeft = currentEntry.getCount();
}
occurrencesLeft--;
canRemove = true;
return currentEntry.getElement();
}
@Override
public void remove() {
checkRemove(canRemove);
int frequency = currentEntry.getCount();
if (frequency <= 0) {
throw new ConcurrentModificationException();
}
if (frequency == 1) {
entryIterator.remove();
} else {
((ObjectCountHashMap.MapEntry) currentEntry).setCount(frequency - 1);
}
size--;
canRemove = false;
}
}
@Override
public int count(@Nullable Object element) {
return backingMap.get(element);
}
// Optional Operations - Modification Operations
/**
* {@inheritDoc}
*
* @throws IllegalArgumentException if the call would result in more than
* {@link Integer#MAX_VALUE} occurrences of {@code element} in this
* multiset.
*/
@CanIgnoreReturnValue
@Override
public int add(@Nullable E element, int occurrences) {
if (occurrences == 0) {
return count(element);
}
checkArgument(occurrences > 0, "occurrences cannot be negative: %s", occurrences);
int oldCount = backingMap.get(element);
long newCount = (long) oldCount + (long) occurrences;
checkArgument(newCount <= Integer.MAX_VALUE, "too many occurrences: %s", newCount);
backingMap.put(element, (int) newCount);
size += occurrences;
return oldCount;
}
@CanIgnoreReturnValue
@Override
public int remove(@Nullable Object element, int occurrences) {
if (occurrences == 0) {
return count(element);
}
checkArgument(occurrences > 0, "occurrences cannot be negative: %s", occurrences);
int oldCount = backingMap.get(element);
int numberRemoved;
if (oldCount > occurrences) {
numberRemoved = occurrences;
backingMap.put((E) element, oldCount - occurrences);
} else {
numberRemoved = oldCount;
backingMap.remove(element);
}
size -= numberRemoved;
return oldCount;
}
// Roughly a 33% performance improvement over AbstractMultiset.setCount().
@CanIgnoreReturnValue
@Override
public int setCount(@Nullable E element, int count) {
checkNonnegative(count, "count");
int oldCount = (count == 0) ? backingMap.remove(element) : backingMap.put(element, count);
size += (count - oldCount);
return oldCount;
}
// Don't allow default serialization.
@GwtIncompatible // java.io.ObjectStreamException
private void readObjectNoData() throws ObjectStreamException {
throw new InvalidObjectException("Stream data required");
}
@GwtIncompatible // not needed in emulated source.
private static final long serialVersionUID = -2250766705698539974L;
}