--- /dev/null	2011-08-08 08:40:49.685541141 -0700
+++ new/src/share/classes/java/util/functions/Reducer.java	2011-08-09 10:55:29.000000000 -0700
@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code 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
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package java.util.functions;
+
+/**
+ * Reduce an input object by combining with a base object.
+ *
+ * <p>All reducer implementations are expected to:
+ * <ul>
+ *  <li>Provide stable results such that for any {@code a} and {@code b} the
+ * result of two {@code reduce} operations are always equivalent. ie.<pre>
+ * Foo one = reducer.reduce(a,b);
+ * Foo two = reducer.reduce(a,b);
+ *
+ * assert one.equals(two) && two.equals(one);
+ * </pre></li>
+ * <li>The reducer should not modify the input object in any way that would
+ * change the result.</li>
+ * <li>When used for aggregate operations upon many elements reducers
+ * should not assume that the {@code reduce} operation will be called upon
+ * elements in any specific orderie.<pre>
+ * Foo one = reducer.reduce(a,reducer.reduce(b,c));
+ * Foo two = reducer.reduce(b,reducer.reduce(a,c));
+ *
+ * assert one.equals(two) && two.equals(one);
+ * </pre>/li>
+ * </ul>
+
+ * @param <T> the type of input objects provided to {@code reduce}.
+ * @param <U> the type of the base value and output objects from {@code reduce}.
+ * This may be the same type as {@code <T>}.
+ */
+public interface Reducer<T, U> {
+
+    /**
+     * Produce a reduced output using the provided input and base objects.
+     *
+     * @param base the reduction base.
+     * @param t the input object.
+     * @return reduced output.
+     */
+    U reduce(U base, T t);
+
+    /**
+     * Returns a reducer which conditionally performs reduce on the input from
+     * {@code <U>} to {@code <T>}. The reduce is only performed if the provided
+     * predicate returns {@code true} for the input {@code <U>}.
+     * @param predicate A Predicate for {@code <U>} values.
+     * @return A reducer which conditionally performing reduction from {@code <U>} to
+     * {@code <T>} if the {@code <U>} input value satisfies a predicate.
+     */
+    Reducer<T, U> compose(Predicate<? super T> predicate) default Reducers.compose;
+
+    /**
+     * Returns a reducer which performs a mapping of inputs from {@code <V>} to
+     * {@code <T>} before reducing to the result.
+     * @param <V> Type of input objects.
+     * @param mapper A mapper from {@code <V>} to {@code <U>}.
+     * @return A reducer which performing a mapping from {@code <U>} to
+     * {@code <V>}prior to reducing from {@code <U>} to {@code <T>}.
+     */
+     <V> Reducer<V, U> compose(Mapper<? super V, ? extends T> mapper) default Reducers.compose;
+}