Index: src/Common/NetTopologySuite/Index/Strtree/AbstractNode.cs
===================================================================
diff -u -r8f6ae890fed8e8eae3a32f9c0498a10f82e0ddf9 -r5fc71a385897af92ccb092f2f969b5709afab85a
--- src/Common/NetTopologySuite/Index/Strtree/AbstractNode.cs	(.../AbstractNode.cs)	(revision 8f6ae890fed8e8eae3a32f9c0498a10f82e0ddf9)
+++ src/Common/NetTopologySuite/Index/Strtree/AbstractNode.cs	(.../AbstractNode.cs)	(revision 5fc71a385897af92ccb092f2f969b5709afab85a)
@@ -8,11 +8,10 @@
     /// (AbstractNodes) or real data (ItemBoundables). If this node contains real data
     /// (rather than nodes), then we say that this node is a "leaf node".
     /// </summary>
-    public abstract class AbstractNode : IBoundable 
+    public abstract class AbstractNode : IBoundable
     {
-        private ArrayList childBoundables = new ArrayList();
+        private readonly ArrayList childBoundables = new ArrayList();
         private object bounds = null;
-        private int level;
 
         /// <summary> 
         /// Constructs an AbstractNode at the given level in the tree
@@ -21,9 +20,9 @@
         /// 0 if this node is a leaf, 1 if a parent of a leaf, and so on; the
         /// root node will have the highest level.
         /// </param>
-        public AbstractNode(int level) 
+        public AbstractNode(int level)
         {
-            this.level = level;
+            Level = level;
         }
 
         /// <summary> 
@@ -39,16 +38,10 @@
         }
 
         /// <summary>
-        /// Returns a representation of space that encloses this Boundable,
-        /// preferably not much bigger than this Boundable's boundary yet fast to
-        /// test for intersection with the bounds of other Boundables. The class of
-        /// object returned depends on the subclass of AbstractSTRtree.
+        /// Returns 0 if this node is a leaf, 1 if a parent of a leaf, and so on; the
+        /// root node will have the highest level.
         /// </summary>
-        /// <returns> 
-        /// An Envelope (for STRtrees), an Interval (for SIRtrees), or other
-        /// object (for other subclasses of AbstractSTRtree).
-        /// </returns>        
-        protected abstract object ComputeBounds();
+        public int Level { get; private set; }
 
         /// <summary>
         /// 
@@ -66,26 +59,26 @@
         }
 
         /// <summary>
-        /// Returns 0 if this node is a leaf, 1 if a parent of a leaf, and so on; the
-        /// root node will have the highest level.
-        /// </summary>
-        public int Level
-        {
-            get
-            {
-                return level;
-            }
-        }
-
-        /// <summary>
         /// Adds either an AbstractNode, or if this is a leaf node, a data object
         /// (wrapped in an ItemBoundable).
         /// </summary>
         /// <param name="childBoundable"></param>
-        public void AddChildBoundable(IBoundable childBoundable) 
+        public void AddChildBoundable(IBoundable childBoundable)
         {
             Assert.IsTrue(bounds == null);
             childBoundables.Add(childBoundable);
         }
+
+        /// <summary>
+        /// Returns a representation of space that encloses this Boundable,
+        /// preferably not much bigger than this Boundable's boundary yet fast to
+        /// test for intersection with the bounds of other Boundables. The class of
+        /// object returned depends on the subclass of AbstractSTRtree.
+        /// </summary>
+        /// <returns> 
+        /// An Envelope (for STRtrees), an Interval (for SIRtrees), or other
+        /// object (for other subclasses of AbstractSTRtree).
+        /// </returns>        
+        protected abstract object ComputeBounds();
     }
-}
+}
\ No newline at end of file