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The DSI utilities are a mishmash of classes accumulated during the last twenty years in projects developed at the DSI (Dipartimento di Scienze dell'Informazione, i.e., Information Sciences Department), now DI (Dipartimento di Informatica, i.e., Informatics Department), of the Universita` degli Studi di Milano.

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package it.unimi.dsi.io;

/*
 * DSI utilities
 *
 * Copyright (C) 2003-2020 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.io.MeasurableInputStream;
import it.unimi.dsi.fastutil.io.RepositionableStream;

import java.io.IOException;
import java.io.Serializable;

/** End-of-stream-only input stream.
 *
 * This stream has length 0, and will always return end-of-file on any read attempt.
 *
 * This class is a singleton. You cannot create a null input stream,
 * but you can obtain an instance of this class using {@link #getInstance()}.
 *
 * @author Sebastiano Vigna
 * @since 0.8
 */

public class NullInputStream extends MeasurableInputStream implements RepositionableStream, Serializable {
	private static final long serialVersionUID = 1L;
	private final static NullInputStream INSTANCE = new NullInputStream();

	private NullInputStream() {}

	@Override
	public int read() { return -1; }

	/** Returns the only instance of this class.
	 *
	 * @return  the only instance of this class.
	 */
	public static NullInputStream getInstance() {
		return INSTANCE;
	}

	private Object readResolve() {
		return INSTANCE;
	}

	@Override
	public long length() {
		return 0;
	}

	@Override
	public long position() {
		return 0;
	}

	@Override
	public void position(long position) throws IOException {
		// TODO: we should specify the semantics out of bounds
		return;
	}
}