1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections4.bag;
18
19 import java.io.IOException;
20 import java.io.ObjectInputStream;
21 import java.io.ObjectOutputStream;
22 import java.io.Serializable;
23 import java.util.Collection;
24 import java.util.HashMap;
25
26 /**
27 * Implements {@code Bag}, using a {@link HashMap} to provide the
28 * data storage. This is the standard implementation of a bag.
29 * <p>
30 * A {@code Bag} stores each object in the collection together with a
31 * count of occurrences. Extra methods on the interface allow multiple copies
32 * of an object to be added or removed at once. It is important to read the
33 * interface Javadoc carefully as several methods violate the
34 * {@link Collection} interface specification.
35 * </p>
36 *
37 * @param <E> the type of elements in this bag
38 * @since 3.0 (previously in main package v2.0)
39 */
40 public class HashBag<E> extends AbstractMapBag<E> implements Serializable {
41
42 /** Serial version lock */
43 private static final long serialVersionUID = -6561115435802554013L;
44
45 /**
46 * Constructs an empty {@link HashBag}.
47 */
48 public HashBag() {
49 super(new HashMap<>());
50 }
51
52 /**
53 * Constructs a bag containing all the members of the given collection.
54 *
55 * @param coll a collection to copy into this bag
56 */
57 public HashBag(final Collection<? extends E> coll) {
58 this();
59 addAll(coll);
60 }
61
62 /**
63 * Read the bag in using a custom routine.
64 *
65 * @param in the input stream
66 * @throws IOException if an error occurs while reading from the stream
67 * @throws ClassNotFoundException if an object read from the stream can not be loaded
68 */
69 private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
70 in.defaultReadObject();
71 super.doReadObject(new HashMap<>(), in);
72 }
73
74 /**
75 * Write the bag out using a custom routine.
76 *
77 * @param out the output stream
78 * @throws IOException if an error occurs while writing to the stream
79 */
80 private void writeObject(final ObjectOutputStream out) throws IOException {
81 out.defaultWriteObject();
82 super.doWriteObject(out);
83 }
84
85 }