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Commons Java API for RDF 1.1
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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.util.Objects;

/**
 * An RDF-1.1
 * Triple, as defined by RDF-1.1 Concepts and Abstract Syntax, a W3C Recommendation published on
 * 25 February 2014.

 *
 * @see RDF-1.1
 * Triple
 */
public interface Triple {

    /**
     * The subject of this triple, which may be either a {@link BlankNode} or an
     * {@link IRI}, which are represented in Commons RDF by the interface
     * {@link BlankNodeOrIRI}.
     *
     * @return The subject {@link BlankNodeOrIRI} of this triple.
     * @see RDF-1.1
     * Triple subject
     */
    BlankNodeOrIRI getSubject();

    /**
     * The predicate {@link IRI} of this triple.
     *
     * @return The predicate {@link IRI} of this triple.
     * @see RDF-1.1
     * Triple predicate
     */
    IRI getPredicate();

    /**
     * The object of this triple, which may be either a {@link BlankNode}, an
     * {@link IRI}, or a {@link Literal}, which are represented in Commons RDF
     * by the interface {@link RDFTerm}.
     *
     * @return The object {@link RDFTerm} of this triple.
     * @see RDF-1.1
     * Triple object
     */
    RDFTerm getObject();

    /**
     * Check it this Triple is equal to another Triple.
     * 
     * Two Triples are equal if and only if their {@link #getSubject()},
     * {@link #getPredicate()} and {@link #getObject()} are equal.
     * 
     * 
     * Implementations MUST also override {@link #hashCode()} so that two equal
     * Triples produce the same hash code.
     * 
     *
     * @param other Another object
     * @return true if other is a Triple and is equal to this
     * @see Object#equals(Object)
     */
    @Override
    public boolean equals(Object other);

    /**
     * Calculate a hash code for this Triple.
     * 
     * The returned hash code MUST be equal to the result
     * of {@link Objects#hash(Object...)} with
     * the arguments
     * {@link #getSubject()}, {@link #getPredicate()}, {@link #getObject()}.
     * 
     * This method MUST be implemented in conjunction with {@link #equals(Object)}
     * so that two equal {@link Triple}s produce the same hash code.
     *
     * @return a hash code value for this Triple.
     * @see Object#hashCode()
     * @see Objects#hash(Object...)
     */
    @Override
    public int hashCode();

}