public class TileId
{
    public static final String WALL = "#";
    public static final String UNEXPLORED = " ";
    public static final String DROID = ".";

    private TileId ()  // prevent instantiation!
    {
    }
}
@@ -107,16 +107,63 @@
  = %22 %22;%0A
+    public static final String TRAVERSE = %22.%22;%0A
     publ
@@ -194,17 +194,17 @@
 ROID = %22
-.
+D
 %22;%0A%0A    

Update TileId.java