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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.collections4;

import org.apache.commons.collections4.bag.CollectionBag;
import org.apache.commons.collections4.bag.HashBag;
import org.apache.commons.collections4.bag.PredicatedBag;
import org.apache.commons.collections4.bag.PredicatedSortedBag;
import org.apache.commons.collections4.bag.SynchronizedBag;
import org.apache.commons.collections4.bag.SynchronizedSortedBag;
import org.apache.commons.collections4.bag.TransformedBag;
import org.apache.commons.collections4.bag.TransformedSortedBag;
import org.apache.commons.collections4.bag.TreeBag;
import org.apache.commons.collections4.bag.UnmodifiableBag;
import org.apache.commons.collections4.bag.UnmodifiableSortedBag;

/**
 * Provides utility methods and decorators for {@link Bag} and {@link SortedBag} instances.
 *
 * @since 2.1
 * @version $Id: BagUtils.java 1686855 2015-06-22 13:00:27Z tn $
 */
public class BagUtils {

    /**
     * An empty unmodifiable bag.
     */
    @SuppressWarnings("rawtypes") // OK, empty bag is compatible with any type
    public static final Bag EMPTY_BAG = UnmodifiableBag.unmodifiableBag(new HashBag());

    /**
     * An empty unmodifiable sorted bag.
     */
    @SuppressWarnings("rawtypes") // OK, empty bag is compatible with any type
    public static final Bag EMPTY_SORTED_BAG =
            UnmodifiableSortedBag.unmodifiableSortedBag(new TreeBag());

    /**
     * Instantiation of BagUtils is not intended or required.
     */
    private BagUtils() {}

    //-----------------------------------------------------------------------
    /**
     * Returns a synchronized (thread-safe) bag backed by the given bag. In
     * order to guarantee serial access, it is critical that all access to the
     * backing bag is accomplished through the returned bag.
     * 

* It is imperative that the user manually synchronize on the returned bag * when iterating over it: * *

     * Bag bag = BagUtils.synchronizedBag(new HashBag());
     * ...
     * synchronized(bag) {
     *     Iterator i = bag.iterator(); // Must be in synchronized block
     *     while (i.hasNext())
     *         foo(i.next());
     *     }
     * }
     * 
* * Failure to follow this advice may result in non-deterministic behavior. * * @param the element type * @param bag the bag to synchronize, must not be null * @return a synchronized bag backed by that bag * @throws NullPointerException if the Bag is null */ public static Bag synchronizedBag(final Bag bag) { return SynchronizedBag.synchronizedBag(bag); } /** * Returns an unmodifiable view of the given bag. Any modification attempts * to the returned bag will raise an {@link UnsupportedOperationException}. * * @param the element type * @param bag the bag whose unmodifiable view is to be returned, must not be null * @return an unmodifiable view of that bag * @throws NullPointerException if the Bag is null */ public static Bag unmodifiableBag(final Bag bag) { return UnmodifiableBag.unmodifiableBag(bag); } /** * Returns a predicated (validating) bag backed by the given bag. *

* Only objects that pass the test in the given predicate can be added to * the bag. Trying to add an invalid object results in an * IllegalArgumentException. It is important not to use the original bag * after invoking this method, as it is a backdoor for adding invalid * objects. * * @param the element type * @param bag the bag to predicate, must not be null * @param predicate the predicate for the bag, must not be null * @return a predicated bag backed by the given bag * @throws NullPointerException if the Bag or Predicate is null */ public static Bag predicatedBag(final Bag bag, final Predicate predicate) { return PredicatedBag.predicatedBag(bag, predicate); } /** * Returns a transformed bag backed by the given bag. *

* Each object is passed through the transformer as it is added to the Bag. * It is important not to use the original bag after invoking this method, * as it is a backdoor for adding untransformed objects. *

* Existing entries in the specified bag will not be transformed. * If you want that behaviour, see {@link TransformedBag#transformedBag(Bag, Transformer)}. * * @param the element type * @param bag the bag to predicate, must not be null * @param transformer the transformer for the bag, must not be null * @return a transformed bag backed by the given bag * @throws NullPointerException if the Bag or Transformer is null */ public static Bag transformingBag(final Bag bag, final Transformer transformer) { return TransformedBag.transformingBag(bag, transformer); } /** * Returns a bag that complies to the Collection contract, backed by the given bag. * * @param the element type * @param bag the bag to decorate, must not be null * @return a Bag that complies to the Collection contract * @throws NullPointerException if bag is null * @since 4.0 */ public static Bag collectionBag(final Bag bag) { return CollectionBag.collectionBag(bag); } //----------------------------------------------------------------------- /** * Returns a synchronized (thread-safe) sorted bag backed by the given * sorted bag. In order to guarantee serial access, it is critical that all * access to the backing bag is accomplished through the returned bag. *

* It is imperative that the user manually synchronize on the returned bag * when iterating over it: * *

     * SortedBag bag = BagUtils.synchronizedSortedBag(new TreeBag());
     * ...
     * synchronized(bag) {
     *     Iterator i = bag.iterator(); // Must be in synchronized block
     *     while (i.hasNext())
     *         foo(i.next());
     *     }
     * }
     * 
* * Failure to follow this advice may result in non-deterministic behavior. * * @param the element type * @param bag the bag to synchronize, must not be null * @return a synchronized bag backed by that bag * @throws NullPointerException if the SortedBag is null */ public static SortedBag synchronizedSortedBag(final SortedBag bag) { return SynchronizedSortedBag.synchronizedSortedBag(bag); } /** * Returns an unmodifiable view of the given sorted bag. Any modification * attempts to the returned bag will raise an * {@link UnsupportedOperationException}. * * @param the element type * @param bag the bag whose unmodifiable view is to be returned, must not be null * @return an unmodifiable view of that bag * @throws NullPointerException if the SortedBag is null */ public static SortedBag unmodifiableSortedBag(final SortedBag bag) { return UnmodifiableSortedBag.unmodifiableSortedBag(bag); } /** * Returns a predicated (validating) sorted bag backed by the given sorted * bag. *

* Only objects that pass the test in the given predicate can be added to * the bag. Trying to add an invalid object results in an * IllegalArgumentException. It is important not to use the original bag * after invoking this method, as it is a backdoor for adding invalid * objects. * * @param the element type * @param bag the sorted bag to predicate, must not be null * @param predicate the predicate for the bag, must not be null * @return a predicated bag backed by the given bag * @throws NullPointerException if the SortedBag or Predicate is null */ public static SortedBag predicatedSortedBag(final SortedBag bag, final Predicate predicate) { return PredicatedSortedBag.predicatedSortedBag(bag, predicate); } /** * Returns a transformed sorted bag backed by the given bag. *

* Each object is passed through the transformer as it is added to the Bag. * It is important not to use the original bag after invoking this method, * as it is a backdoor for adding untransformed objects. *

* Existing entries in the specified bag will not be transformed. * If you want that behaviour, see * {@link TransformedSortedBag#transformedSortedBag(SortedBag, Transformer)}. * * @param the element type * @param bag the bag to predicate, must not be null * @param transformer the transformer for the bag, must not be null * @return a transformed bag backed by the given bag * @throws NullPointerException if the Bag or Transformer is null */ public static SortedBag transformingSortedBag(final SortedBag bag, final Transformer transformer) { return TransformedSortedBag.transformingSortedBag(bag, transformer); } /** * Get an empty Bag. * * @param the element type * @return an empty Bag */ @SuppressWarnings("unchecked") // OK, empty bag is compatible with any type public static Bag emptyBag() { return (Bag) EMPTY_BAG; } /** * Get an empty SortedBag. * * @param the element type * @return an empty sorted Bag */ @SuppressWarnings("unchecked") // OK, empty bag is compatible with any type public static SortedBag emptySortedBag() { return (SortedBag) EMPTY_SORTED_BAG; } }