common.PlainObjectReference: For storing an object in a HashSet/HashMap, ignoring custom hashCode/equals

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@10895 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/common/PlainObjectReference.java

@@ -0,0 +1,84 @@
+//==============================================================================
+//	
+//	Copyright (c) 2015-
+//	Authors:
+//	* Joachim Klein <klein@tcs.inf.tu-dresden.de> (TU Dresden)
+//	
+//------------------------------------------------------------------------------
+//	
+//	This file is part of PRISM.
+//	
+//	PRISM is free software; you can redistribute it and/or modify
+//	it under the terms of the GNU General Public License as published by
+//	the Free Software Foundation; either version 2 of the License, or
+//	(at your option) any later version.
+//	
+//	PRISM is distributed in the hope that it will be useful,
+//	but WITHOUT ANY WARRANTY; without even the implied warranty of
+//	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//	GNU General Public License for more details.
+//	
+//	You should have received a copy of the GNU General Public License
+//	along with PRISM; if not, write to the Free Software Foundation,
+//	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+//	
+//==============================================================================
+
+package common;
+
+/**
+ * Helper class that wraps some other object and strips away
+ * custom implementations of {@code hashCode} and {@code equals}.
+ *
+ * This is useful for storing objects that have such custom implementations
+ * in a HashSet or HashMap when the goal is to maintain the distinction
+ * between different Java objects, even though they might test equal via
+ * {@code equals}.
+ *
+ * A PlainObjectReference wraps another object and provides {@code hashCode}
+ * via {@code System.identityHashCode} and {@code equals} via equality checking
+ * with the {@code ==} operator, i.e., what would happen using the
+ * default implementation of {@code Object}.
+ *
+ * @param <T> the type of the underlying class
+ */
+public class PlainObjectReference<T>
+{
+	/** The object that is referenced */
+	private T object;
+
+	/** Constructor, take reference to object */
+	public PlainObjectReference(T object)
+	{
+		this.object = object;
+	}
+
+	/** Get the referenced object */
+	public T getObject()
+	{
+		return object;
+	}
+
+	@Override
+	public int hashCode()
+	{
+		// return the identityHashCode of the referenced object,
+		// just as it would happen if there were no {@code hashCode}
+		// method in the object
+		return System.identityHashCode(object);
+	}
+
+	@Override
+	public boolean equals(Object obj)
+	{
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (!(obj instanceof PlainObjectReference))
+			return false;
+		PlainObjectReference<?> other = (PlainObjectReference<?>) obj;
+		// test for equality via ==
+		return other.object == object;
+	}
+}