Added ObjectUtil.compare(Comparable,Comparable) which sorts nulls before

non-nulls; added ComparableTuple which sorts first on its left element (nulls
sorting before non-nulls) and then on its right.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@2265 6335cc39-0255-0410-8fd6-9bcaacd3b74c

src/java/com/samskivert/util/ComparableTuple.java

@@ -0,0 +1,51 @@
+//
+// $Id$
+//
+// samskivert library - useful routines for java programs
+// Copyright (C) 2001-2007 Michael Bayne
+// 
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library 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
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.util;
+
+/**
+ * A pair of {@link Comparable} objects that is itself {@link Comparable}.
+ */
+public class ComparableTuple<L extends Comparable<? super L>, R extends Comparable<? super R>>
+    extends Tuple<L,R>
+    implements Comparable<ComparableTuple<L,R>>
+{
+    /**
+     * Constructs a tuple with the supplied contents.
+     */
+    public ComparableTuple (L left, R right)
+    {
+        super(left, right);
+    }
+
+    /**
+     * Constructs a blank tuple.
+     */
+    public ComparableTuple ()
+    {
+    }
+
+    // from interface Comparable
+    public int compareTo (ComparableTuple<L, R> other)
+    {
+        int rv = ObjectUtil.compareTo(left, other.left);
+        return (rv != 0) ? rv : ObjectUtil.compareTo(right, other.right);
+    }
+}

src/java/com/samskivert/util/ObjectUtil.java

@@ -50,6 +50,23 @@ public class ObjectUtil
                 Arrays.equals(t1.getStackTrace(), t2.getStackTrace()));
     }
 
+    /**
+     * Compares two objects, returning -1 if left is null and right is not and 1 if left is
+     * non-null and right is null.
+     */
+    public static <T extends Comparable<? super T>> int compareTo (T left, T right)
+    {
+        if (left == null && right == null) {
+            return 0;
+        } else if (left == null) {
+            return -1;
+        } else if (right == null) {
+            return 1;
+        } else {
+            return left.compareTo(right);
+        }
+    }
+
     /**
      * Dumps the contents of the supplied object instance, listing the
      * class name, hash code and <code>toString()</code> data for each