/*
* Copyright 2001-2004 The Apache Software Foundation
*
* 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 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.
* <p>
* Suppose you have a Bag that contains <code>{a, a, b, c}</code>.
* Calling {@link #getCount(Object)} on <code>a</code> would return 2, while
* calling {@link #uniqueSet()} would return <code>{a, b, c}</code>.
* <p>
* <i>NOTE: This interface violates the {@link Collection} contract.</i>
* The behavior specified in many of these methods is <i>not</i> the same
* as the behavior specified by <code>Collection</code>.
* The noncompliant methods are clearly marked with "(Violation)".
* Exercise caution when using a bag as a <code>Collection</code>.
* <p>
* 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: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @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);
/**
* <i>(Violation)</i>
* Adds one copy the specified object to the Bag.
* <p>
* 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.
* <p>
* Since this method always increases the size of the bag,
* according to the {@link Collection#add(Object)} contract, it
* should always return <code>true</code>. Since it sometimes returns
* <code>false</code>, this method violates the contract.
*
* @param object the object to add
* @return <code>true</code> if the object was not already in the <code>uniqueSet</code>
*/
boolean add(Object object);
/**
* Adds <code>nCopies</code> copies of the specified object to the Bag.
* <p>
* 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 <code>nCopies</code>.
*
* @param object the object to add
* @param nCopies the number of copies to add
* @return <code>true</code> if the object was not already in the <code>uniqueSet</code>
*/
boolean add(Object object, int nCopies);
/**
* <i>(Violation)</i>
* Removes all occurrences of the given object from the bag.
* <p>
* This will also remove the object from the {@link #uniqueSet()}.
* <p>
* According to the {@link Collection#remove(Object)} method,
* this method should only remove the <i>first</i> occurrence of the
* given object, not <i>all</i> occurrences.
*
* @return <code>true</code> if this call changed the collection
*/
boolean remove(Object object);
/**
* Removes <code>nCopies</code> copies of the specified object from the Bag.
* <p>
* 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 <code>true</code> if this call changed the collection
*/
boolean remove(Object object, int nCopies);
/**
* Returns a {@link Set} of unique elements in the Bag.
* <p>
* 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();
/**
* <i>(Violation)</i>
* Returns <code>true</code> if the bag contains all elements in
* the given collection, respecting cardinality. That is, if the
* given collection <code>coll</code> contains <code>n</code> copies
* of a given object, calling {@link #getCount(Object)} on that object must
* be <code>>= n</code> for all <code>n</code> in <code>coll</code>.
* <p>
* The {@link Collection#containsAll(Collection)} method specifies
* that cardinality should <i>not</i> 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 <code>true</code> if the Bag contains all the collection
*/
boolean containsAll(Collection coll);
/**
* <i>(Violation)</i>
* Remove all elements represented in the given collection,
* respecting cardinality. That is, if the given collection
* <code>coll</code> contains <code>n</code> copies of a given object,
* the bag will have <code>n</code> fewer copies, assuming the bag
* had at least <code>n</code> copies to begin with.
*
* <P>The {@link Collection#removeAll(Collection)} method specifies
* that cardinality should <i>not</i> be respected; this method should
* remove <i>all</i> occurrences of every object contained in the
* given collection.
*
* @param coll the collection to remove
* @return <code>true</code> if this call changed the collection
*/
boolean removeAll(Collection coll);
/**
* <i>(Violation)</i>
* Remove any members of the bag that are not in the given
* collection, respecting cardinality. That is, if the given
* collection <code>coll</code> contains <code>n</code> copies of a
* given object and the bag has <code>m > n</code> copies, then
* delete <code>m - n</code> copies from the bag. In addition, if
* <code>e</code> is an object in the bag but
* <code>!coll.contains(e)</code>, then remove <code>e</code> and any
* of its copies.
*
* <P>The {@link Collection#retainAll(Collection)} method specifies
* that cardinality should <i>not</i> be respected; this method should
* keep <i>all</i> occurrences of every object contained in the
* given collection.
*
* @param coll the collection to retain
* @return <code>true</code> 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
// * <code>(e==null ? 0 : e.hashCode()) ^ noOccurances)</code>.
// * This hash code definition is compatible with the Set interface.
// *
// * @return the hash code of the Bag
// */
// int hashCode();
}