GH-5015 improvements to AbstractIRI and models

Author: hmottestad

core/model-api/src/main/java/org/eclipse/rdf4j/model/base/AbstractIRI.java

@@ -45,9 +45,23 @@ public boolean equals(Object o) {
 		return false;
 	}
 
+	private int cachedHashCode = 0;
+
 	@Override
 	public int hashCode() {
-		return stringValue().hashCode();
+		int cached = cachedHashCode;
+		if (cached == 0) {
+			synchronized (this) {
+				cached = cachedHashCode;
+				if (cached == 0) {
+					cached = stringValue().hashCode();
+					cachedHashCode = cached;
+				}
+			}
+			cached = stringValue().hashCode();
+			cachedHashCode = cached;
+		}
+		return cached;
 	}
 
 	@Override

core/model/src/main/java/org/eclipse/rdf4j/model/impl/AbstractModel.java

@@ -31,6 +31,7 @@
 public abstract class AbstractModel extends AbstractSet<Statement> implements Model {
 
 	private static final long serialVersionUID = 4254119331281455614L;
+	public static final Resource[] NULL_CONTEXT = { null };
 
 	@Override
 	public Model unmodifiable() {
@@ -179,6 +180,9 @@ public boolean remove(Object o) {
 	public boolean contains(Object o) {
 		if (o instanceof Statement) {
 			Statement st = (Statement) o;
+			if (st.getContext() == null) {
+				return contains(st.getSubject(), st.getPredicate(), st.getObject(), NULL_CONTEXT);
+			}
 			return contains(st.getSubject(), st.getPredicate(), st.getObject(), st.getContext());
 		}
 		return false;

core/model/src/main/java/org/eclipse/rdf4j/model/impl/LinkedHashModel.java

@@ -420,6 +420,13 @@ public boolean equals(Object other) {
 			if (this == other) {
 				return true;
 			}
+			if (other == null) {
+				return false;
+			}
+			if (other == statement) {
+				return true;
+			}
+
 			if (!super.equals(other)) {
 				return false;
 			}