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The S-Space Package is a Natural Language Processing library for distributional semantics representations. Distributional semantics representations model the meaning of words, phrases, and sentences as high dimensional vectors or probability distributions. The library includes common algorithms such as Latent Semantic Analysis, Random Indexing, and Latent Dirichlet Allocation. The S-Space package also includes software libraries for matrices, vectors, graphs, and numerous clustering algorithms.

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/*
 * Copyright 2009 David Jurgens
 *
 * This file is part of the S-Space package and is covered under the terms and
 * conditions therein.
 *
 * The S-Space package is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation and distributed hereunder to you.
 *
 * THIS SOFTWARE IS PROVIDED "AS IS" AND NO REPRESENTATIONS OR WARRANTIES,
 * EXPRESS OR IMPLIED ARE MADE.  BY WAY OF EXAMPLE, BUT NOT LIMITATION, WE MAKE
 * NO REPRESENTATIONS OR WARRANTIES OF MERCHANT- ABILITY OR FITNESS FOR ANY
 * PARTICULAR PURPOSE OR THAT THE USE OF THE LICENSED SOFTWARE OR DOCUMENTATION
 * WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER
 * RIGHTS.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see .
 */

package edu.ucla.sspace.util;

import java.util.Comparator;
import java.util.Map;
import java.util.TreeMap;

/**
 * A {@code Map} implementation that grows to a fixed size and then retains only
 * a fixed number of the highest (largest) keys.  All keys used in this class
 * must implements {@link Comparable}.
 *
 * @see BoundedSortedMultiMap
 */
public class BoundedSortedMap extends TreeMap {

    private static final long serialVersionUID = 1;

    /**
     * The maximum number of mappings to retain.
     */
    private final int bound;
    
    /**
     * Creatins an instance that will only retain the specified number of the
     * largest (highest) keys.
     *
     * @param bound the number of mappings to retain
     */
    public BoundedSortedMap(int bound) {
	this(bound, true);
    }

    /**
     * Creatins an instance that will only retain the specified number of keys,
     * where the largest (highest) keys.
     *
     * @param bound the number of mappings to retain
     * @param retainHighest {@code true} if the highest elements are to be
     *        retained, {@code false} if the lowest keys are to be retained
     */
    public BoundedSortedMap(int bound, boolean retainHighest) {
	super(((retainHighest) ? null : new ReverseComparator()));
	this.bound = bound;
    }

    /**
     * Adds the key-value mapping to this map, and if the total number of
     * mappings exceeds the bounds, removes either the currently lowest element,
     * or if reversed, the currently highest element.
     *
     * @param key {@inheritDoc}
     * @param value {@inheritDoc}
     */
    public V put(K key, V value) {
	V old = super.put(key, value);
	if (size() > bound) {
	    remove(firstKey());
	}
	return old;
    }

    /**
     * Adds all of the key-value mapping to this map, and if the total number of
     * mappings exceeds the bounds, removes mappings until the size is within
     * bounds.
     *
     * @param m {@inheritDoc}
     */
    public void putAll(Map m) {
	for (Map.Entry e : m.entrySet()) {
	    put(e.getKey(), e.getValue());
	}
    }

    /**
     * A comparator that results in the opposite ordering of the natural
     * ordering from {@link Comparator#compareTo(Object,Object) compareTo}.
     */
    static final class ReverseComparator 
            implements Comparator, java.io.Serializable {

        private static final long serialVersionUID = 1;
	
	// Assume that if the comparator is being used that the objects are
	// instances of Comparable
	@SuppressWarnings("unchecked")
	public int compare(K c1, K c2) {
	    return -(((Comparable)c1).compareTo(c2));
	}
    }
}