1 /**
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package org.apache.commons.rdf.api;
19
20 import java.util.Objects;
21
22 /**
23 * An <a href= "http://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple" >RDF-1.1
24 * Triple</a>, as defined by
25 * <a href= "http://www.w3.org/TR/rdf11-concepts/" >RDF-1.1 Concepts and
26 * Abstract Syntax</a>, a W3C Recommendation published on 25 February 2014.
27 * <p>
28 * A <code>Triple</code> object in Commons RDF is considered
29 * <strong>immutable</strong>, that is, over its life time it will have
30 * consistent behaviour for its {@link #equals(Object)}, and the {@link RDFTerm}
31 * instances returned from {@link #getSubject()}, {@link #getPredicate()} and
32 * {@link #getObject()} will have consistent {@link RDFTerm#equals(Object)}
33 * behaviour.
34 * <p>
35 * Note that <code>Triple</code> methods are not required to return object
36 * identical (<code>==</code>) instances as long as they are equivalent
37 * according to {@link RDFTerm#equals(Object)}. Specialisations of
38 * <code>Triple</code> may provide additional methods that are documented to be
39 * mutable.
40 * <p>
41 * <code>Triple</code> methods are <strong>thread-safe</strong>, however
42 * specialisations may provide additional methods that are documented to not be
43 * thread-safe.
44 * <p>
45 * <code>Triple</code>s can be safely used in hashing collections like
46 * {@link java.util.HashSet} and {@link java.util.HashMap}.
47 * <p>
48 * Any <code>Triple</code> can be used interchangeably across Commons RDF
49 * implementations.
50 *
51 * @see Quad
52 * @see RDF#createTriple(BlankNodeOrIRI,IRI,RDFTerm)
53 * @see <a href= "http://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple" >RDF-1.1
54 * Triple</a>
55 */
56 public interface Triple extends TripleLike {
57
58 /**
59 * The subject of this triple, which may be either a {@link BlankNode} or an
60 * {@link IRI}, which are represented in Commons RDF by the interface
61 * {@link BlankNodeOrIRI}.
62 *
63 * @return The subject {@link BlankNodeOrIRI} of this triple.
64 * @see <a href="http://www.w3.org/TR/rdf11-concepts/#dfn-subject">RDF-1.1
65 * Triple subject</a>
66 */
67 @Override
68 BlankNodeOrIRI getSubject();
69
70 /**
71 * The predicate {@link IRI} of this triple.
72 *
73 * @return The predicate {@link IRI} of this triple.
74 * @see <a href="http://www.w3.org/TR/rdf11-concepts/#dfn-predicate">RDF-1.1
75 * Triple predicate</a>
76 */
77 @Override
78 IRI getPredicate();
79
80 /**
81 * The object of this triple, which may be either a {@link BlankNode}, an
82 * {@link IRI}, or a {@link Literal}, which are represented in Commons RDF
83 * by the interface {@link RDFTerm}.
84 *
85 * @return The object {@link RDFTerm} of this triple.
86 * @see <a href="http://www.w3.org/TR/rdf11-concepts/#dfn-object">RDF-1.1
87 * Triple object</a>
88 */
89 @Override
90 RDFTerm getObject();
91
92 /**
93 * Check it this Triple is equal to another Triple.
94 * <p>
95 * Two Triples are equal if and only if their {@link #getSubject()},
96 * {@link #getPredicate()} and {@link #getObject()} are equal.
97 * </p>
98 * <p>
99 * Implementations MUST also override {@link #hashCode()} so that two equal
100 * Triples produce the same hash code.
101 * </p>
102 *
103 * @param other
104 * Another object
105 * @return true if other is a Triple and is equal to this
106 * @see Object#equals(Object)
107 */
108 @Override
109 public boolean equals(Object other);
110
111 /**
112 * Calculate a hash code for this Triple.
113 * <p>
114 * The returned hash code MUST be equal to the result of
115 * {@link Objects#hash(Object...)} with the arguments {@link #getSubject()},
116 * {@link #getPredicate()}, {@link #getObject()}.
117 * <p>
118 * This method MUST be implemented in conjunction with
119 * {@link #equals(Object)} so that two equal {@link Triple}s produce the
120 * same hash code.
121 *
122 * @return a hash code value for this Triple.
123 * @see Object#hashCode()
124 * @see Objects#hash(Object...)
125 */
126 @Override
127 public int hashCode();
128
129 }