Add singleton ObjectToStringComparator.INSTANCE.

src/changes/changes.xml

@@ -119,6 +119,9 @@
     <action dev="ggregory" type="add" due-to="Gary Gregory">
       Add ListUtils.getFirst() and getLast().
     </action>
+    <action dev="ggregory" type="add" due-to="Gary Gregory">
+      Add singleton ObjectToStringComparator.INSTANCE.
+    </action>
     <!-- UPDATE -->
     <action type="update" dev="kinow" due-to="Dependabot">
       Bump actions/setup-java from v1.4.0 to v2 #174 #177 #186 #224.

src/test/java/org/apache/commons/collections4/junit/ObjectToStringComparator.java

@@ -22,6 +22,13 @@ import java.util.Comparator;
 
 public final class ObjectToStringComparator implements Comparator<Object>, Serializable {
 
+    /**
+     * Singleton instance.
+     *
+     * @since 4.5
+     */
+    public final ObjectToStringComparator INSTANCE = new ObjectToStringComparator();
+
     private static final long serialVersionUID = 1L;
 
     @Override