org.apache.commons.rdf.api.Literal.java Source code

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Here is the source code for org.apache.commons.rdf.api.Literal.java

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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.rdf.api;

import java.io.Serializable;
import java.util.Objects;
import java.util.Optional;

/**
 * A RDF-1.1 Literal, 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
 */
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()}.
     *
     * 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 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>
     *
     * 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()}.
     * <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();

}