org.lenskit.util.keys.Keys.java Source code

Introduction

Here is the source code for org.lenskit.util.keys.Keys.java

Source

/*
 * LensKit, an open source recommender systems toolkit.
 * Copyright 2010-2014 LensKit Contributors.  See CONTRIBUTORS.md.
 * Work on LensKit has been funded by the National Science Foundation under
 * grants IIS 05-34939, 08-08692, 08-12148, and 10-17697.
 *
 * This program 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 program 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
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */
package org.lenskit.util.keys;

import com.google.common.collect.Ordering;
import com.google.common.primitives.Longs;

/**
 * Utility class for key extractors.
 */
public final class Keys {
    private Keys() {
    }

    public static <T> Ordering<T> keyOrdering(final KeyExtractor<T> ex) {
        return new Ordering<T>() {
            @Override
            public int compare(T left, T right) {
                return Longs.compare(ex.getKey(left), ex.getKey(right));
            }
        };
    }

    public static KeyExtractor<KeyedObject> selfExtractor() {
        return SelfExtractor.INSTANCE;
    }

    enum SelfExtractor implements KeyExtractor<KeyedObject> {
        INSTANCE {
            @Override
            public long getKey(KeyedObject obj) {
                return obj.getKey();
            }
        }
    }
}