| /** |
| * 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.rdf.api; |
| |
| import java.io.Serializable; |
| import java.util.Locale; |
| import java.util.Objects; |
| import java.util.Optional; |
| |
| /** |
| * An <a href= "https://www.w3.org/TR/rdf11-concepts/#dfn-literal" |
| * >RDF-1.1 Literal</a>, as defined by |
| * <a href= "http://www.w3.org/TR/rdf11-concepts/#section-Graph-Literal" |
| * >RDF-1.1 Concepts and Abstract Syntax</a>, a W3C Recommendation published on |
| * 25 February 2014. |
| * |
| * @see RDF#createLiteral(String) |
| * @see RDF#createLiteral(String, IRI) |
| * @see RDF#createLiteral(String, String) |
| */ |
| public interface Literal extends RDFTerm { |
| |
| /** |
| * The lexical form of this literal, represented by a |
| * <a href="http://www.unicode.org/versions/latest/">Unicode string</a>. |
| * |
| * @return The lexical form of this literal. |
| * @see <a href= |
| * "http://www.w3.org/TR/rdf11-concepts/#dfn-lexical-form">RDF-1.1 |
| * Literal lexical form</a> |
| */ |
| String getLexicalForm(); |
| |
| /** |
| * The IRI identifying the datatype that determines how the lexical form |
| * maps to a literal value. |
| * |
| * If the datatype IRI is |
| * <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#langString" |
| * >http://www.w3.org/1999/02/22-rdf-syntax-ns#langString</a>, |
| * {@link #getLanguageTag()} must not return {@link Optional#empty()}, and |
| * it must return a valid |
| * <a href="http://tools.ietf.org/html/bcp47">BCP47</a> language tag. |
| * |
| * @return The datatype IRI for this literal. |
| * @see <a href= |
| * "http://www.w3.org/TR/rdf11-concepts/#dfn-datatype-iri">RDF-1.1 |
| * Literal datatype IRI</a> |
| */ |
| IRI getDatatype(); |
| |
| /** |
| * If and only if the datatype IRI is |
| * <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#langString" |
| * >http://www.w3.org/1999/02/22-rdf-syntax-ns#langString</a>, the language |
| * tag for this Literal is a non-empty language tag as defined by |
| * <a href="http://tools.ietf.org/html/bcp47">BCP47</a>.<br> |
| * If the datatype IRI is not |
| * <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#langString" |
| * >http://www.w3.org/1999/02/22-rdf-syntax-ns#langString</a>, this method |
| * must return {@link Optional#empty()}. |
| * <p> |
| * The value space of language tags is always in lower case; although |
| * RDF implementations MAY convert all language tags to lower case, |
| * safe comparisons of language tags should be done using |
| * {@link String#toLowerCase(Locale)} with the locale |
| * {@link Locale#ROOT}. |
| * <p> |
| * Implementation note: If your application requires {@link Serializable} |
| * objects, it is best not to store an {@link Optional} in a field. It is |
| * recommended to use {@link Optional#ofNullable(Object)} to create the |
| * return value for this method. |
| * |
| * @return The {@link Optional} language tag for this literal. If |
| * {@link Optional#isPresent()} returns true, the value returned by |
| * {@link Optional#get()} must be a non-empty language tag string |
| * conforming to BCP47. |
| * @see <a href= |
| * "http://www.w3.org/TR/rdf11-concepts/#dfn-language-tag">RDF-1.1 |
| * Literal language tag</a> |
| */ |
| Optional<String> getLanguageTag(); |
| |
| /** |
| * Check it this Literal is equal to another Literal. |
| * <blockquote> |
| * <a href="http://www.w3.org/TR/rdf11-concepts/#dfn-literal-term">Literal |
| * term equality</a>: |
| * Two literals are term-equal (the same RDF literal) if |
| * and only if the two lexical forms, the two datatype IRIs, and the two |
| * language tags (if any) compare equal, character by character. Thus, two |
| * literals can have the same value without being the same RDF term. |
| * </blockquote> |
| * As the value space for language tags is lower-space, if they are present, |
| * they MUST be compared character by character |
| * using the equivalent of {@link String#toLowerCase(java.util.Locale)} with |
| * the locale {@link Locale#ROOT}. |
| * <p> |
| * Implementations MUST also override {@link #hashCode()} so that two equal |
| * Literals produce the same hash code. |
| * |
| * @param other |
| * Another object |
| * @return true if other is a Literal and is equal to this |
| * @see Object#equals(Object) |
| */ |
| @Override |
| public boolean equals(Object other); |
| |
| /** |
| * Calculate a hash code for this Literal. |
| * <p> |
| * The returned hash code MUST be equal to the result of |
| * {@link Objects#hash(Object...)} with the arguments |
| * {@link #getLexicalForm()}, {@link #getDatatype()}, |
| * {@link #getLanguageTag()}<code>.map(s->s.toLowerString(Locale.ROOT))</code>. |
| * <p> |
| * This method MUST be implemented in conjunction with |
| * {@link #equals(Object)} so that two equal Literals produce the same hash |
| * code. |
| * |
| * @return a hash code value for this Literal. |
| * @see Object#hashCode() |
| * @see Objects#hash(Object...) |
| */ |
| @Override |
| public int hashCode(); |
| |
| } |