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MG4J (Managing Gigabytes for Java) is a free full-text search engine for large document collections written in Java. The big version is a fork of the original MG4J that can handle more than 2^31 terms and documents.

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package it.unimi.dsi.big.mg4j.document;

/*		 
 * MG4J: Managing Gigabytes for Java (big)
 *
 * Copyright (C) 2005-2011 Paolo Boldi and Sebastiano Vigna 
 *
 *  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 3 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 program; if not, see .
 *
 */

import it.unimi.dsi.fastutil.objects.Reference2ObjectMap;
import it.unimi.dsi.lang.FlyweightPrototype;

import java.io.IOException;
import java.io.InputStream;

/** A collection of documents.
 * 
 * Classes implementing this interface have additional responsibilities
 * w.r.t. {@link it.unimi.dsi.big.mg4j.document.DocumentSequence} in that they
 * must provide random access to the documents, and guarantee the possibility
 * of multiple calls to {@link it.unimi.dsi.big.mg4j.document.DocumentSequence#iterator()}.
 * 
 * 
Note, however, that the objects returned by 
 * {@link it.unimi.dsi.big.mg4j.document.DocumentSequence#iterator() iterator()},
 * {@link #stream(long)} and {@link #document(long)} are, unless explicitly stated otherwise,
 * mutually exclusive. They share a single resource managed by the
 * collection (and disposed by a call to {@link java.io.Closeable#close() close()}), so each time
 * a stream or a document are returned by some method, the ones previously returned are no longer
 * valid, and access to their methods will cause unpredictable behaviour. If you need many
 * documents, you can {@linkplain FlyweightPrototype#copy() obtain a flyweight copy}
 * of the collection. 
 * 
 * Warning: implementations of this class are not required
 * to be thread-safe, but they provide {@linkplain FlyweightPrototype flyweight copies}.
 * The {@link #copy()} method is strengthened so to return a instance of this class.
 */

public interface DocumentCollection extends DocumentSequence, FlyweightPrototype {
	/** The default extension for a serialised collection (including the dot). */
	public final static String DEFAULT_EXTENSION = ".collection";
	
	/** Returns the number of documents in this collection.
	 * 
	 * @return the number of documents in this collection.
	 */
	public long size();
	
	/** Returns the document given its index.
	 *
	 * @param index an index between 0 (inclusive) and {@link #size()} (exclusive).
	 * @return the index-th document.
	 */
	public Document document( long index ) throws IOException;

	/** Returns an input stream for the raw content of a document.
	 * 
	 * @param index an index between 0 (inclusive) and {@link #size()} (exclusive).
	 * @return the raw content of the document as an input stream.
	 */
	public InputStream stream( long index ) throws IOException;

	/** Returns the metadata map for a document.
	 * 
	 * @param index an index between 0 (inclusive) and {@link #size()} (exclusive).
	 * @return the metadata map for the document.
	 */
	public Reference2ObjectMap,Object> metadata( long index ) throws IOException;
	
	public DocumentCollection copy();
}