1 /*
2 * #%L
3 * EmptyDocument.java - mongodb-async-driver - Allanbank Consulting, Inc.
4 * %%
5 * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.
6 * %%
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 * #L%
19 */
20 package com.allanbank.mongodb.bson.impl;
21
22 import java.util.Collections;
23 import java.util.List;
24 import java.util.Map;
25
26 import com.allanbank.mongodb.bson.Element;
27
28 /**
29 * An immutable empty document.
30 *
31 * @api.yes This interface is part of the driver's API. Public and protected
32 * members will be deprecated for at least 1 non-bugfix release
33 * (version numbers are <major>.<minor>.<bugfix>)
34 * before being removed or modified.
35 * @copyright 2011, Allanbank Consulting, Inc., All Rights Reserved
36 */
37 public class EmptyDocument extends AbstractDocument {
38
39 /** An instance of the Empty Document. */
40 public static final EmptyDocument INSTANCE = new EmptyDocument();
41
42 /**
43 * The bytes to encode an empty document. Length (4) + terminal null (1) =
44 * 5.
45 */
46 public static final int SIZE = 5;
47
48 /** Serialization version for the class. */
49 private static final long serialVersionUID = -2775918328146027036L;
50
51 /**
52 * Constructs a new {@link EmptyDocument}.
53 */
54 public EmptyDocument() {
55 super();
56 }
57
58 /**
59 * {@inheritDoc}
60 * <p>
61 * Overridden to return an empty list of elements.
62 * </p>
63 *
64 * @return The elements in the document.
65 */
66 @Override
67 public List<Element> getElements() {
68 return Collections.emptyList();
69 }
70
71 /**
72 * Returns the size of the empty document when encoded as bytes. This is
73 * always 5 bytes.
74 *
75 * @return The size of the document when encoded as bytes.
76 */
77 @Override
78 public long size() {
79 return SIZE; // length (4) + terminal null (1).
80 }
81
82 /**
83 * {@inheritDoc}
84 * <p>
85 * Overridden to return an empty map as this document is always empty.
86 * </p>
87 */
88 @Override
89 protected Map<String, Element> getElementMap() {
90 return Collections.emptyMap();
91 }
92 }