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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 2010 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.dependency;

import java.util.HashMap;
import java.util.Map;


/**
 * A coordinating utility class for managing all the {@link DependencyExtractor}
 * instances responsible for reading all of the different dependency parsing
 * output formats.  This class provides access to a default {@code
 * DependencyExtractor}, which is the set either explicitly, or is set when the
 * first {@link DependencyExtractor} is added.  This class also provides access
 * to {@link DependencyExtractor} instances by name in the event than a user
 * should need to process a format generated by a specific parser.
 */
public class DependencyExtractorManager {

    // REMDINER: it might be useful to have the Manager create the extractor if
    // it isn't already present, but can be created on the fly.  -david

    /**
     * The default extractor to return.
     */
    private static DependencyExtractor defaultExtractor;

    /**
     * A mapping from the parser name to the {@link DependencyExtractor} can
     * read to the extractor instance.
     */
    private static Map nameToExtractor =
        new HashMap();

    /**
     * Uninstantiable
     */
    private DependencyExtractorManager() { }

    /**
     * Adds the provided {@link DependencyExtractor} to the set of available
     * extractors.  If an existing extractor has the same name, the existing
     * extactor is overwritten.  If no extractors have been added, the provided
     * extractor becomes the default extractor.
     *
     * @param name the name of the parser that generated the parse trees.
     * @param extractor the an extractor instance
     *
     * @throws NullPointerException if either {@code name} or {@code extractor}
     *         are {@code null}.
     */
    public static synchronized void addExtractor(
        String name, DependencyExtractor extractor) {
        addExtractor(name, extractor, defaultExtractor == null);
    }

    /**
     * Adds the provided {@link DependencyExtractor} to the set of available
     * extractors, optionally setting the extractor as the default.  If an
     * existing extractor has the same name, the existing extactor is
     * overwritten.
     *
     * @param name the name of the parser that generated the parse trees.
     * @param extractor the extractor instance
     * @param isDefault {@code true} if this extractor should be the default
     *        returned by this class
     *
     * @throws NullPointerException if either {@code name} or {@code extractor}
     *         are {@code null}.
     */
    public static synchronized void addExtractor(
        String name, DependencyExtractor extractor, boolean isDefault) {
               
        if (extractor == null)
            throw new NullPointerException("Extractor cannot be null" + name);
        if (name == null)
            throw new NullPointerException("Extractor cannot have null name");
        nameToExtractor.put(name, extractor);
        if (isDefault)
            defaultExtractor = extractor;
    }
    
    /**
     * Returns the extractor with the specified name.  The name typically refers
     * to the parser that generated the output files that the extractor can
     * read.
     *
     * @param name the name associated with an extractor.
     *
     * @throws IllegalArgumentException if no extractor is known for the {@code
     *         name}
     */
    public static synchronized DependencyExtractor getExtractor(String name) {
        DependencyExtractor e = nameToExtractor.get(name);
        if (e == null)
            throw new IllegalArgumentException("No extactor with name " + name);
        return e;
    }

    /**
     * Returns the default extractor used by this manager.
     *
     * @throws IllegalStateException if no default extractor has been set
     */
    public static synchronized DependencyExtractor getDefaultExtractor() {
        if (defaultExtractor == null)
            throw new IllegalStateException(
                "No DependencyExtractors available.");
        return defaultExtractor;
    }
}