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	/*
	* Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code 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
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.io;

	import java.io.InputStream;
	import java.util.Enumeration;
	import java.util.Vector;

	/**
	* A <code>SequenceInputStream</code> represents
	* the logical concatenation of other input
	* streams. It starts out with an ordered
	* collection of input streams and reads from
	* the first one until end of file is reached,
	* whereupon it reads from the second one,
	* and so on, until end of file is reached
	* on the last of the contained input streams.
	*
	* @author Author van Hoff
	* @since JDK1.0
	*/
	public
	class SequenceInputStream extends InputStream {
	Enumeration<? extends InputStream> e;
	InputStream in;

	/**
	* Initializes a newly created <code>SequenceInputStream</code>
	* by remembering the argument, which must
	* be an <code>Enumeration</code> that produces
	* objects whose run-time type is <code>InputStream</code>.
	* The input streams that are produced by
	* the enumeration will be read, in order,
	* to provide the bytes to be read from this
	* <code>SequenceInputStream</code>. After
	* each input stream from the enumeration
	* is exhausted, it is closed by calling its
	* <code>close</code> method.
	*
	* @param e an enumeration of input streams.
	* @see java.util.Enumeration
	*/
	public SequenceInputStream(Enumeration<? extends InputStream> e) {
	this.e = e;
	try {
	nextStream();
	} catch (IOException ex) {
	// This should never happen
	throw new Error("panic");
	}
	}

	/**
	* Initializes a newly
	* created <code>SequenceInputStream</code>
	* by remembering the two arguments, which
	* will be read in order, first <code>s1</code>
	* and then <code>s2</code>, to provide the
	* bytes to be read from this <code>SequenceInputStream</code>.
	*
	* @param s1 the first input stream to read.
	* @param s2 the second input stream to read.
	*/
	public SequenceInputStream(InputStream s1, InputStream s2) {
	Vector<InputStream> v = new Vector<>(2);

	v.addElement(s1);
	v.addElement(s2);
	e = v.elements();
	try {
	nextStream();
	} catch (IOException ex) {
	// This should never happen
	throw new Error("panic");
	}
	}

	/**
	* Continues reading in the next stream if an EOF is reached.
	*/
	final void nextStream() throws IOException {
	if (in != null) {
	in.close();
	}

	if (e.hasMoreElements()) {
	in = (InputStream) e.nextElement();
	if (in == null)
	throw new NullPointerException();
	}
	else in = null;

	}

	/**
	* Returns an estimate of the number of bytes that can be read (or
	* skipped over) from the current underlying input stream without
	* blocking by the next invocation of a method for the current
	* underlying input stream. The next invocation might be
	* the same thread or another thread. A single read or skip of this
	* many bytes will not block, but may read or skip fewer bytes.
	* <p>
	* This method simply calls {@code available} of the current underlying
	* input stream and returns the result.
	*
	* @return an estimate of the number of bytes that can be read (or
	* skipped over) from the current underlying input stream
	* without blocking or {@code 0} if this input stream
	* has been closed by invoking its {@link #close()} method
	* @exception IOException if an I/O error occurs.
	*
	* @since JDK1.1
	*/
	public int available() throws IOException {
	if (in == null) {
	return 0; // no way to signal EOF from available()
	}
	return in.available();
	}

	/**
	* Reads the next byte of data from this input stream. The byte is
	* returned as an <code>int</code> in the range <code>0</code> to
	* <code>255</code>. If no byte is available because the end of the
	* stream has been reached, the value <code>-1</code> is returned.
	* This method blocks until input data is available, the end of the
	* stream is detected, or an exception is thrown.
	* <p>
	* This method
	* tries to read one character from the current substream. If it
	* reaches the end of the stream, it calls the <code>close</code>
	* method of the current substream and begins reading from the next
	* substream.
	*
	* @return the next byte of data, or <code>-1</code> if the end of the
	* stream is reached.
	* @exception IOException if an I/O error occurs.
	*/
	public int read() throws IOException {
	while (in != null) {
	int c = in.read();
	if (c != -1) {
	return c;
	}
	nextStream();
	}
	return -1;
	}

	/**
	* Reads up to <code>len</code> bytes of data from this input stream
	* into an array of bytes. If <code>len</code> is not zero, the method
	* blocks until at least 1 byte of input is available; otherwise, no
	* bytes are read and <code>0</code> is returned.
	* <p>
	* The <code>read</code> method of <code>SequenceInputStream</code>
	* tries to read the data from the current substream. If it fails to
	* read any characters because the substream has reached the end of
	* the stream, it calls the <code>close</code> method of the current
	* substream and begins reading from the next substream.
	*
	* @param b the buffer into which the data is read.
	* @param off the start offset in array <code>b</code>
	* at which the data is written.
	* @param len the maximum number of bytes read.
	* @return int the number of bytes read.
	* @exception NullPointerException If <code>b</code> is <code>null</code>.
	* @exception IndexOutOfBoundsException If <code>off</code> is negative,
	* <code>len</code> is negative, or <code>len</code> is greater than
	* <code>b.length - off</code>
	* @exception IOException if an I/O error occurs.
	*/
	public int read(byte b[], int off, int len) throws IOException {
	if (in == null) {
	return -1;
	} else if (b == null) {
	throw new NullPointerException();
	} else if (off < 0 \|\| len < 0 \|\| len > b.length - off) {
	throw new IndexOutOfBoundsException();
	} else if (len == 0) {
	return 0;
	}
	do {
	int n = in.read(b, off, len);
	if (n > 0) {
	return n;
	}
	nextStream();
	} while (in != null);
	return -1;
	}

	/**
	* Closes this input stream and releases any system resources
	* associated with the stream.
	* A closed <code>SequenceInputStream</code>
	* cannot perform input operations and cannot
	* be reopened.
	* <p>
	* If this stream was created
	* from an enumeration, all remaining elements
	* are requested from the enumeration and closed
	* before the <code>close</code> method returns.
	*
	* @exception IOException if an I/O error occurs.
	*/
	public void close() throws IOException {
	do {
	nextStream();
	} while (in != null);
	}
	}

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