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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.multiset;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import org.apache.commons.collections4.IteratorUtils;
import org.apache.commons.collections4.MultiSet;
import org.apache.commons.collections4.Transformer;
/**
* Abstract implementation of the {@link MultiSet} interface to simplify the
* creation of subclass implementations.
*
* @param the type held in the multiset
* @since 4.1
*/
public abstract class AbstractMultiSet extends AbstractCollection implements MultiSet {
/** View of the elements */
private transient Set uniqueSet;
/** View of the entries */
private transient Set> entrySet;
/**
* Constructor needed for subclass serialisation.
*/
protected AbstractMultiSet() {
super();
}
//-----------------------------------------------------------------------
/**
* Returns the number of elements in this multiset.
*
* @return current size of the multiset
*/
@Override
public int size() {
int totalSize = 0;
for (final Entry entry : entrySet()) {
totalSize += entry.getCount();
}
return totalSize;
}
/**
* Returns the number of occurrence of the given element in this multiset by
* iterating over its entrySet.
*
* @param object the object to search for
* @return the number of occurrences of the object, zero if not found
*/
@Override
public int getCount(final Object object) {
for (final Entry entry : entrySet()) {
final E element = entry.getElement();
if (element == object ||
element != null && element.equals(object)) {
return entry.getCount();
}
}
return 0;
}
@Override
public int setCount(final E object, final int count) {
if (count < 0) {
throw new IllegalArgumentException("Count must not be negative.");
}
final int oldCount = getCount(object);
if (oldCount < count) {
add(object, count - oldCount);
} else {
remove(object, oldCount - count);
}
return oldCount;
}
//-----------------------------------------------------------------------
/**
* Determines if the multiset contains the given element.
*
* @param object the object to search for
* @return true if the multiset contains the given element
*/
@Override
public boolean contains(final Object object) {
return getCount(object) > 0;
}
//-----------------------------------------------------------------------
/**
* Gets an iterator over the multiset elements. Elements present in the
* MultiSet more than once will be returned repeatedly.
*
* @return the iterator
*/
@Override
public Iterator iterator() {
return new MultiSetIterator<>(this);
}
/**
* Inner class iterator for the MultiSet.
*/
private static class MultiSetIterator implements Iterator {
private final AbstractMultiSet parent;
private final Iterator> entryIterator;
private Entry current;
private int itemCount;
private boolean canRemove;
/**
* Constructor.
*
* @param parent the parent multiset
*/
public MultiSetIterator(final AbstractMultiSet parent) {
this.parent = parent;
this.entryIterator = parent.entrySet().iterator();
this.current = null;
this.canRemove = false;
}
/** {@inheritDoc} */
@Override
public boolean hasNext() {
return itemCount > 0 || entryIterator.hasNext();
}
/** {@inheritDoc} */
@Override
public E next() {
if (itemCount == 0) {
current = entryIterator.next();
itemCount = current.getCount();
}
canRemove = true;
itemCount--;
return current.getElement();
}
/** {@inheritDoc} */
@Override
public void remove() {
if (canRemove == false) {
throw new IllegalStateException();
}
final int count = current.getCount();
if (count > 1) {
parent.remove(current.getElement());
} else {
entryIterator.remove();
}
canRemove = false;
}
}
//-----------------------------------------------------------------------
@Override
public boolean add(final E object) {
add(object, 1);
return true;
}
@Override
public int add(final E object, final int occurrences) {
throw new UnsupportedOperationException();
}
//-----------------------------------------------------------------------
/**
* Clears the multiset removing all elements from the entrySet.
*/
@Override
public void clear() {
final Iterator> it = entrySet().iterator();
while (it.hasNext()) {
it.next();
it.remove();
}
}
@Override
public boolean remove(final Object object) {
return remove(object, 1) != 0;
}
@Override
public int remove(final Object object, final int occurrences) {
throw new UnsupportedOperationException();
}
@Override
public boolean removeAll(final Collection coll) {
boolean result = false;
final Iterator i = coll.iterator();
while (i.hasNext()) {
final Object obj = i.next();
final boolean changed = remove(obj, getCount(obj)) != 0;
result = result || changed;
}
return result;
}
//-----------------------------------------------------------------------
/**
* Returns a view of the unique elements of this multiset.
*
* @return the set of unique elements in this multiset
*/
@Override
public Set uniqueSet() {
if (uniqueSet == null) {
uniqueSet = createUniqueSet();
}
return uniqueSet;
}
/**
* Create a new view for the set of unique elements in this multiset.
*
* @return a view of the set of unique elements
*/
protected Set createUniqueSet() {
return new UniqueSet<>(this);
}
/**
* Creates a unique set iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the uniqueSet iterator
*/
protected Iterator createUniqueSetIterator() {
final Transformer, E> transformer = new Transformer, E>() {
@Override
public E transform(final Entry entry) {
return entry.getElement();
}
};
return IteratorUtils.transformedIterator(entrySet().iterator(), transformer);
}
/**
* Returns an unmodifiable view of the entries of this multiset.
*
* @return the set of entries in this multiset
*/
@Override
public Set> entrySet() {
if (entrySet == null) {
entrySet = createEntrySet();
}
return entrySet;
}
/**
* Create a new view for the set of entries in this multiset.
*
* @return a view of the set of entries
*/
protected Set> createEntrySet() {
return new EntrySet<>(this);
}
/**
* Returns the number of unique elements in this multiset.
*
* @return the number of unique elements
*/
protected abstract int uniqueElements();
/**
* Creates an entry set iterator.
* Subclasses can override this to return iterators with different properties.
*
* @return the entrySet iterator
*/
protected abstract Iterator> createEntrySetIterator();
//-----------------------------------------------------------------------
/**
* Inner class UniqueSet.
*/
protected static class UniqueSet extends AbstractSet {
/** The parent multiset */
protected final AbstractMultiSet parent;
/**
* Constructs a new unique element view of the MultiSet.
*
* @param parent the parent MultiSet
*/
protected UniqueSet(final AbstractMultiSet parent) {
this.parent = parent;
}
@Override
public Iterator iterator() {
return parent.createUniqueSetIterator();
}
@Override
public boolean contains(final Object key) {
return parent.contains(key);
}
@Override
public boolean containsAll(final Collection coll) {
return parent.containsAll(coll);
}
@Override
public boolean remove(final Object key) {
return parent.remove(key, parent.getCount(key)) != 0;
}
@Override
public int size() {
return parent.uniqueElements();
}
@Override
public void clear() {
parent.clear();
}
}
//-----------------------------------------------------------------------
/**
* Inner class EntrySet.
*/
protected static class EntrySet extends AbstractSet> {
private final AbstractMultiSet parent;
/**
* Constructs a new view of the MultiSet.
*
* @param parent the parent MultiSet
*/
protected EntrySet(final AbstractMultiSet parent) {
this.parent = parent;
}
@Override
public int size() {
return parent.uniqueElements();
}
@Override
public Iterator> iterator() {
return parent.createEntrySetIterator();
}
@Override
public boolean contains(final Object obj) {
if (obj instanceof Entry == false) {
return false;
}
final Entry entry = (Entry) obj;
final Object element = entry.getElement();
return parent.getCount(element) == entry.getCount();
}
@Override
public boolean remove(final Object obj) {
if (obj instanceof Entry == false) {
return false;
}
final Entry entry = (Entry) obj;
final Object element = entry.getElement();
if (parent.contains(element)) {
final int count = parent.getCount(element);
if (entry.getCount() == count) {
parent.remove(element, count);
return true;
}
}
return false;
}
}
/**
* Inner class AbstractEntry.
*/
protected static abstract class AbstractEntry implements Entry {
@Override
public boolean equals(final Object object) {
if (object instanceof Entry) {
final Entry other = (Entry) object;
final E element = this.getElement();
final Object otherElement = other.getElement();
return this.getCount() == other.getCount() &&
(element == otherElement ||
element != null && element.equals(otherElement));
}
return false;
}
@Override
public int hashCode() {
final E element = getElement();
return ((element == null) ? 0 : element.hashCode()) ^ getCount();
}
@Override
public String toString() {
return String.format("%s:%d", getElement(), getCount());
}
}
//-----------------------------------------------------------------------
/**
* Write the multiset out using a custom routine.
* @param out the output stream
* @throws IOException any of the usual I/O related exceptions
*/
protected void doWriteObject(final ObjectOutputStream out) throws IOException {
out.writeInt(entrySet().size());
for (final Entry entry : entrySet()) {
out.writeObject(entry.getElement());
out.writeInt(entry.getCount());
}
}
/**
* Read the multiset in using a custom routine.
* @param in the input stream
* @throws IOException any of the usual I/O related exceptions
* @throws ClassNotFoundException if the stream contains an object which class can not be loaded
* @throws ClassCastException if the stream does not contain the correct objects
*/
protected void doReadObject(final ObjectInputStream in)
throws IOException, ClassNotFoundException {
final int entrySize = in.readInt();
for (int i = 0; i < entrySize; i++) {
@SuppressWarnings("unchecked") // This will fail at runtime if the stream is incorrect
final E obj = (E) in.readObject();
final int count = in.readInt();
setCount(obj, count);
}
}
//-----------------------------------------------------------------------
@Override
public boolean equals(final Object object) {
if (object == this) {
return true;
}
if (object instanceof MultiSet == false) {
return false;
}
final MultiSet other = (MultiSet) object;
if (other.size() != size()) {
return false;
}
for (final Entry entry : entrySet()) {
if (other.getCount(entry.getElement()) != getCount(entry.getElement())) {
return false;
}
}
return true;
}
@Override
public int hashCode() {
return entrySet().hashCode();
}
/**
* Implement a toString() method suitable for debugging.
*
* @return a debugging toString
*/
@Override
public String toString() {
return entrySet().toString();
}
}