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* 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.collections;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
/**
* Defines a collection that counts the number of times an object appears in
* the collection.
*
* Suppose you have a Bag that contains {a, a, b, c}.
* Calling {@link #getCount(Object)} on a would return 2, while
* calling {@link #uniqueSet()} would return {a, b, c}.
*
* NOTE: This interface violates the {@link Collection} contract.
* The behavior specified in many of these methods is not the same
* as the behavior specified by Collection.
* The noncompliant methods are clearly marked with "(Violation)".
* Exercise caution when using a bag as a Collection.
*
* This violation resulted from the original specification of this interface.
* In an ideal world, the interface would be changed to fix the problems, however
* it has been decided to maintain backwards compatibility instead.
*
* @since Commons Collections 2.0
* @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
*
* @author Chuck Burdick
* @author Stephen Colebourne
*/
public interface Bag extends Collection {
/**
* Returns the number of occurrences (cardinality) of the given
* object currently in the bag. If the object does not exist in the
* bag, return 0.
*
* @param object the object to search for
* @return the number of occurrences of the object, zero if not found
*/
int getCount(Object object);
/**
* (Violation)
* Adds one copy the specified object to the Bag.
*
* If the object is already in the {@link #uniqueSet()} then increment its
* count as reported by {@link #getCount(Object)}. Otherwise add it to the
* {@link #uniqueSet()} and report its count as 1.
*
* Since this method always increases the size of the bag,
* according to the {@link Collection#add(Object)} contract, it
* should always return true. Since it sometimes returns
* false, this method violates the contract.
*
* @param object the object to add
* @return true if the object was not already in the uniqueSet
*/
boolean add(Object object);
/**
* Adds nCopies copies of the specified object to the Bag.
*
* If the object is already in the {@link #uniqueSet()} then increment its
* count as reported by {@link #getCount(Object)}. Otherwise add it to the
* {@link #uniqueSet()} and report its count as nCopies.
*
* @param object the object to add
* @param nCopies the number of copies to add
* @return true if the object was not already in the uniqueSet
*/
boolean add(Object object, int nCopies);
/**
* (Violation)
* Removes all occurrences of the given object from the bag.
*
* This will also remove the object from the {@link #uniqueSet()}.
*
* According to the {@link Collection#remove(Object)} method,
* this method should only remove the first occurrence of the
* given object, not all occurrences.
*
* @return true if this call changed the collection
*/
boolean remove(Object object);
/**
* Removes nCopies copies of the specified object from the Bag.
*
* If the number of copies to remove is greater than the actual number of
* copies in the Bag, no error is thrown.
*
* @param object the object to remove
* @param nCopies the number of copies to remove
* @return true if this call changed the collection
*/
boolean remove(Object object, int nCopies);
/**
* Returns a {@link Set} of unique elements in the Bag.
*
* Uniqueness constraints are the same as those in {@link java.util.Set}.
*
* @return the Set of unique Bag elements
*/
Set uniqueSet();
/**
* Returns the total number of items in the bag across all types.
*
* @return the total size of the Bag
*/
int size();
/**
* (Violation)
* Returns true if the bag contains all elements in
* the given collection, respecting cardinality. That is, if the
* given collection coll contains n copies
* of a given object, calling {@link #getCount(Object)} on that object must
* be >= n for all n in coll.
*
* The {@link Collection#containsAll(Collection)} method specifies
* that cardinality should not be respected; this method should
* return true if the bag contains at least one of every object contained
* in the given collection.
*
* @param coll the collection to check against
* @return true if the Bag contains all the collection
*/
boolean containsAll(Collection coll);
/**
* (Violation)
* Remove all elements represented in the given collection,
* respecting cardinality. That is, if the given collection
* coll contains n copies of a given object,
* the bag will have n fewer copies, assuming the bag
* had at least n copies to begin with.
*
*
The {@link Collection#removeAll(Collection)} method specifies
* that cardinality should not be respected; this method should
* remove all occurrences of every object contained in the
* given collection.
*
* @param coll the collection to remove
* @return true if this call changed the collection
*/
boolean removeAll(Collection coll);
/**
* (Violation)
* Remove any members of the bag that are not in the given
* collection, respecting cardinality. That is, if the given
* collection coll contains n copies of a
* given object and the bag has m > n copies, then
* delete m - n copies from the bag. In addition, if
* e is an object in the bag but
* !coll.contains(e), then remove e and any
* of its copies.
*
*
The {@link Collection#retainAll(Collection)} method specifies
* that cardinality should not be respected; this method should
* keep all occurrences of every object contained in the
* given collection.
*
* @param coll the collection to retain
* @return true if this call changed the collection
*/
boolean retainAll(Collection coll);
/**
* Returns an {@link Iterator} over the entire set of members,
* including copies due to cardinality. This iterator is fail-fast
* and will not tolerate concurrent modifications.
*
* @return iterator over all elements in the Bag
*/
Iterator iterator();
// The following is not part of the formal Bag interface, however where possible
// Bag implementations should follow these comments.
// /**
// * Compares this Bag to another.
// * This Bag equals another Bag if it contains the same number of occurrences of
// * the same elements.
// * This equals definition is compatible with the Set interface.
// *
// * @param obj the Bag to compare to
// * @return true if equal
// */
// boolean equals(Object obj);
//
// /**
// * Gets a hash code for the Bag compatible with the definition of equals.
// * The hash code is defined as the sum total of a hash code for each element.
// * The per element hash code is defined as
// * (e==null ? 0 : e.hashCode()) ^ noOccurances).
// * This hash code definition is compatible with the Set interface.
// *
// * @return the hash code of the Bag
// */
// int hashCode();
}