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 * 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
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package org.apache.commons.collections4;

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 getCount(Object) on a would return 2, while calling uniqueSet() would return {a, b, c}.


NOTE: This interface violates the 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.

Type parameters:
<E> – the type of elements in this bag
Since:
2.0/**
 * 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>
 * <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>
 * <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.
 * </p>
 *
 * @param <E> the type of elements in this bag
 * @since 2.0
 */
public interface Bag<E> extends Collection<E> {

    
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.
Params:
object –  the object to search for
Returns:
the number of occurrences of the object, zero if not found/**
     * 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 of the specified object to the Bag.
 If the object is already in the uniqueSet() then increment its count as reported by getCount(Object). Otherwise add it to the uniqueSet() and report its count as 1. 
 Since this method always increases the size of the bag, according to the Collection.add(Object) contract, it should always return true.  Since it sometimes returns
false, this method violates the contract.

Params:
object –  the object to add
Returns:
true if the object was not already in the uniqueSet/**
     * <i>(Violation)</i>
     * Adds one copy 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 1.
     * </p>
     * <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.
     * </p>
     *
     * @param object  the object to add
     * @return <code>true</code> if the object was not already in the <code>uniqueSet</code>
     */
    @Override
    boolean add(E object);

    
Adds nCopies copies of the specified object to the Bag.
 If the object is already in the uniqueSet() then increment its count as reported by getCount(Object). Otherwise add it to the uniqueSet() and report its count as nCopies.

Params:
object –  the object to add
nCopies –  the number of copies to add
Returns:
true if the object was not already in the uniqueSet/**
     * 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>.
     * </p>
     *
     * @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(E object, int nCopies);

    
(Violation)
Removes all occurrences of the given object from the bag.
 This will also remove the object from the uniqueSet(). 
 According to the Collection.remove(Object) method, this method should only remove the first occurrence of the
given object, not all occurrences.

Params:
object –  the object to remove
Returns:
true if this call changed the collection/**
     * <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>
     * <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.
     * </p>
     *
     * @param object  the object to remove
     * @return <code>true</code> if this call changed the collection
     */
    @Override
    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.

Params:
object –  the object to remove
nCopies –  the number of copies to remove
Returns:
true if this call changed the collection/**
     * 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.
     * </p>
     *
     * @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 Set of unique elements in the Bag. 
 Uniqueness constraints are the same as those in Set. 
Returns:
the Set of unique Bag elements/**
     * Returns a {@link Set} of unique elements in the Bag.
     * <p>
     * Uniqueness constraints are the same as those in {@link java.util.Set}.
     * </p>
     *
     * @return the Set of unique Bag elements
     */
    Set<E> uniqueSet();

    
Returns the total number of items in the bag across all types.
Returns:
the total size of the Bag/**
     * Returns the total number of items in the bag across all types.
     *
     * @return the total size of the Bag
     */
    @Override
    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 getCount(Object) on that object must be >= n for all n in coll.
 The 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.

Params:
coll –  the collection to check against
Returns:
true if the Bag contains all the collection/**
     * <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>&gt;= 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.
     * </p>
     *
     * @param coll  the collection to check against
     * @return <code>true</code> if the Bag contains all the collection
     */
    @Override
    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 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.

Params:
coll –  the collection to remove
Returns:
true if this call changed the collection/**
     * <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.
     * </p>
     *
     * @param coll  the collection to remove
     * @return <code>true</code> if this call changed the collection
     */
    @Override
    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 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.

Params:
coll –  the collection to retain
Returns:
true if this call changed the collection/**
     * <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 &gt; 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.
     * </p>
     *
     * @param coll  the collection to retain
     * @return <code>true</code> if this call changed the collection
     */
    @Override
    boolean retainAll(Collection<?> coll);

    
Returns an Iterator over the entire set of members, including copies due to cardinality. This iterator is fail-fast and will not tolerate concurrent modifications. 
Returns:
iterator over all elements in the Bag/**
     * 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
     */
    @Override
    Iterator<E> 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();

}