com.google.common.collect.AbstractMapBasedMultiset Maven / Gradle / Ivy
/*
* 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 java.io.InvalidObjectException;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nullable;
/**
* Basic implementation of {@code Multiset} backed by an instance of {@code
* Map}.
*
* For serialization to work, the subclass must specify explicit {@code
* readObject} and {@code writeObject} methods.
*
* @author Kevin Bourrillion
*/
@GwtCompatible(emulated = true)
abstract class AbstractMapBasedMultiset extends AbstractMultiset
implements Serializable {
private transient Map 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(Map backingMap) {
this.backingMap = checkNotNull(backingMap);
this.size = super.size();
}
/** Used during deserialization only. The backing map must be empty. */
void setBackingMap(Map backingMap) {
this.backingMap = backingMap;
}
// Required Implementations
/**
* {@inheritDoc}
*
* 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> entrySet() {
return super.entrySet();
}
@Override
Iterator> entryIterator() {
final Iterator> backingEntries =
backingMap.entrySet().iterator();
return new Iterator>() {
Map.Entry toRemove;
@Override
public boolean hasNext() {
return backingEntries.hasNext();
}
@Override
public Multiset.Entry next() {
final Map.Entry mapEntry = backingEntries.next();
toRemove = mapEntry;
return new Multisets.AbstractEntry() {
@Override
public E getElement() {
return mapEntry.getKey();
}
@Override
public int getCount() {
Count count = mapEntry.getValue();
if (count == null || count.get() == 0) {
Count frequency = backingMap.get(getElement());
if (frequency != null) {
return frequency.get();
}
}
return (count == null) ? 0 : count.get();
}
};
}
@Override
public void remove() {
checkRemove(toRemove != null);
size -= toRemove.getValue().getAndSet(0);
backingEntries.remove();
toRemove = null;
}
};
}
@Override
public void clear() {
for (Count frequency : backingMap.values()) {
frequency.set(0);
}
backingMap.clear();
size = 0L;
}
@Override
int distinctElements() {
return backingMap.size();
}
// Optimizations - Query Operations
@Override public int size() {
return Ints.saturatedCast(size);
}
@Override public Iterator iterator() {
return new MapBasedMultisetIterator();
}
/*
* Not subclassing AbstractMultiset$MultisetIterator because next() needs to
* retrieve the Map.Entry entry, which can then be used for
* a more efficient remove() call.
*/
private class MapBasedMultisetIterator implements Iterator {
final Iterator> entryIterator;
Map.Entry currentEntry;
int occurrencesLeft;
boolean canRemove;
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.getValue().get();
}
occurrencesLeft--;
canRemove = true;
return currentEntry.getKey();
}
@Override
public void remove() {
checkRemove(canRemove);
int frequency = currentEntry.getValue().get();
if (frequency <= 0) {
throw new ConcurrentModificationException();
}
if (currentEntry.getValue().addAndGet(-1) == 0) {
entryIterator.remove();
}
size--;
canRemove = false;
}
}
@Override public int count(@Nullable Object element) {
Count frequency = Maps.safeGet(backingMap, element);
return (frequency == null) ? 0 : frequency.get();
}
// 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.
*/
@Override public int add(@Nullable E element, int occurrences) {
if (occurrences == 0) {
return count(element);
}
checkArgument(
occurrences > 0, "occurrences cannot be negative: %s", occurrences);
Count frequency = backingMap.get(element);
int oldCount;
if (frequency == null) {
oldCount = 0;
backingMap.put(element, new Count(occurrences));
} else {
oldCount = frequency.get();
long newCount = (long) oldCount + (long) occurrences;
checkArgument(newCount <= Integer.MAX_VALUE,
"too many occurrences: %s", newCount);
frequency.getAndAdd(occurrences);
}
size += occurrences;
return oldCount;
}
@Override public int remove(@Nullable Object element, int occurrences) {
if (occurrences == 0) {
return count(element);
}
checkArgument(
occurrences > 0, "occurrences cannot be negative: %s", occurrences);
Count frequency = backingMap.get(element);
if (frequency == null) {
return 0;
}
int oldCount = frequency.get();
int numberRemoved;
if (oldCount > occurrences) {
numberRemoved = occurrences;
} else {
numberRemoved = oldCount;
backingMap.remove(element);
}
frequency.addAndGet(-numberRemoved);
size -= numberRemoved;
return oldCount;
}
// Roughly a 33% performance improvement over AbstractMultiset.setCount().
@Override public int setCount(@Nullable E element, int count) {
checkNonnegative(count, "count");
Count existingCounter;
int oldCount;
if (count == 0) {
existingCounter = backingMap.remove(element);
oldCount = getAndSet(existingCounter, count);
} else {
existingCounter = backingMap.get(element);
oldCount = getAndSet(existingCounter, count);
if (existingCounter == null) {
backingMap.put(element, new Count(count));
}
}
size += (count - oldCount);
return oldCount;
}
private static int getAndSet(Count i, int count) {
if (i == null) {
return 0;
}
return i.getAndSet(count);
}
// Don't allow default serialization.
@GwtIncompatible("java.io.ObjectStreamException")
@SuppressWarnings("unused") // actually used during deserialization
private void readObjectNoData() throws ObjectStreamException {
throw new InvalidObjectException("Stream data required");
}
@GwtIncompatible("not needed in emulated source.")
private static final long serialVersionUID = -2250766705698539974L;
}