Github user stain commented on a diff in the pull request:
https://github.com/apache/incubator-commonsrdf/pull/24#discussion_r81328382
--- Diff: rdf4j/src/main/java/org/apache/commons/rdf/rdf4j/RDF4JIRI.java ---
@@ -0,0 +1,35 @@
+/**
+ * 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.rdf4j;
+
+/**
+ * Marker interface for RDF4J implementations of IRI.
+ *
+ */
+public interface RDF4JIRI
+ extends RDF4JTerm<org.eclipse.rdf4j.model.IRI>,
org.apache.commons.rdf.api.IRI {
+
+ /**
+ * Return the corresponding RDF4J {@link org.eclipse.rdf4j.model.IRI}.
+ *
+ * @return The corresponding RDF4J IRI
+ */
+ public org.eclipse.rdf4j.model.IRI asValue();
--- End diff --
http://www.javapractices.com/topic/TopicAction.do?Id=17 says
>
If you extend a concrete class, and add a new field which contributes to
equals, then it's not possible to write a perfectly correct equals method for
the new class. Instead, you should use composition instead of inheritance. (See
Effective Java by Joshua Bloch for more information.)
So in Commons RDF and RDF4J it's possible to do such inheritance because
both have a defined `.equals()` - however that is also what prevents them from
being directly compatible in `RDF4JIRI`. Thus `RDF4JIRIImpl` uses composition.
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