228 lines
8.3 KiB
Java
228 lines
8.3 KiB
Java
/*
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* Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.io;
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import java.io.InputStream;
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import java.util.Enumeration;
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import java.util.Vector;
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/**
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* A <code>SequenceInputStream</code> represents
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* the logical concatenation of other input
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* streams. It starts out with an ordered
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* collection of input streams and reads from
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* the first one until end of file is reached,
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* whereupon it reads from the second one,
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* and so on, until end of file is reached
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* on the last of the contained input streams.
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*
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* @author Author van Hoff
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* @since 1.0
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*/
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public
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class SequenceInputStream extends InputStream {
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Enumeration<? extends InputStream> e;
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InputStream in;
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/**
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* Initializes a newly created <code>SequenceInputStream</code>
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* by remembering the argument, which must
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* be an <code>Enumeration</code> that produces
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* objects whose run-time type is <code>InputStream</code>.
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* The input streams that are produced by
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* the enumeration will be read, in order,
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* to provide the bytes to be read from this
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* <code>SequenceInputStream</code>. After
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* each input stream from the enumeration
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* is exhausted, it is closed by calling its
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* <code>close</code> method.
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*
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* @param e an enumeration of input streams.
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* @see java.util.Enumeration
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*/
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public SequenceInputStream(Enumeration<? extends InputStream> e) {
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this.e = e;
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peekNextStream();
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}
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/**
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* Initializes a newly
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* created <code>SequenceInputStream</code>
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* by remembering the two arguments, which
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* will be read in order, first <code>s1</code>
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* and then <code>s2</code>, to provide the
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* bytes to be read from this <code>SequenceInputStream</code>.
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*
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* @param s1 the first input stream to read.
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* @param s2 the second input stream to read.
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*/
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public SequenceInputStream(InputStream s1, InputStream s2) {
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Vector<InputStream> v = new Vector<>(2);
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v.addElement(s1);
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v.addElement(s2);
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e = v.elements();
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peekNextStream();
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}
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/**
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* Continues reading in the next stream if an EOF is reached.
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*/
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final void nextStream() throws IOException {
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if (in != null) {
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in.close();
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}
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peekNextStream();
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}
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private void peekNextStream() {
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if (e.hasMoreElements()) {
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in = (InputStream) e.nextElement();
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if (in == null)
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throw new NullPointerException();
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} else {
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in = null;
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}
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}
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/**
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* Returns an estimate of the number of bytes that can be read (or
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* skipped over) from the current underlying input stream without
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* blocking by the next invocation of a method for the current
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* underlying input stream. The next invocation might be
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* the same thread or another thread. A single read or skip of this
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* many bytes will not block, but may read or skip fewer bytes.
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* <p>
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* This method simply calls {@code available} of the current underlying
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* input stream and returns the result.
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*
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* @return an estimate of the number of bytes that can be read (or
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* skipped over) from the current underlying input stream
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* without blocking or {@code 0} if this input stream
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* has been closed by invoking its {@link #close()} method
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* @exception IOException if an I/O error occurs.
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*
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* @since 1.1
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*/
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public int available() throws IOException {
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if (in == null) {
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return 0; // no way to signal EOF from available()
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}
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return in.available();
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}
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/**
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* Reads the next byte of data from this input stream. The byte is
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* returned as an <code>int</code> in the range <code>0</code> to
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* <code>255</code>. If no byte is available because the end of the
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* stream has been reached, the value <code>-1</code> is returned.
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* This method blocks until input data is available, the end of the
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* stream is detected, or an exception is thrown.
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* <p>
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* This method
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* tries to read one character from the current substream. If it
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* reaches the end of the stream, it calls the <code>close</code>
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* method of the current substream and begins reading from the next
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* substream.
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*
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* @return the next byte of data, or <code>-1</code> if the end of the
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* stream is reached.
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* @exception IOException if an I/O error occurs.
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*/
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public int read() throws IOException {
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while (in != null) {
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int c = in.read();
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if (c != -1) {
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return c;
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}
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nextStream();
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}
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return -1;
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}
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/**
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* Reads up to <code>len</code> bytes of data from this input stream
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* into an array of bytes. If <code>len</code> is not zero, the method
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* blocks until at least 1 byte of input is available; otherwise, no
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* bytes are read and <code>0</code> is returned.
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* <p>
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* The <code>read</code> method of <code>SequenceInputStream</code>
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* tries to read the data from the current substream. If it fails to
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* read any characters because the substream has reached the end of
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* the stream, it calls the <code>close</code> method of the current
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* substream and begins reading from the next substream.
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*
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* @param b the buffer into which the data is read.
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* @param off the start offset in array <code>b</code>
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* at which the data is written.
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* @param len the maximum number of bytes read.
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* @return int the number of bytes read.
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* @exception NullPointerException If <code>b</code> is <code>null</code>.
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* @exception IndexOutOfBoundsException If <code>off</code> is negative,
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* <code>len</code> is negative, or <code>len</code> is greater than
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* <code>b.length - off</code>
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* @exception IOException if an I/O error occurs.
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*/
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public int read(byte b[], int off, int len) throws IOException {
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if (in == null) {
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return -1;
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} else if (b == null) {
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throw new NullPointerException();
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} else if (off < 0 || len < 0 || len > b.length - off) {
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throw new IndexOutOfBoundsException();
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} else if (len == 0) {
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return 0;
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}
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do {
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int n = in.read(b, off, len);
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if (n > 0) {
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return n;
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}
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nextStream();
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} while (in != null);
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return -1;
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}
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/**
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* Closes this input stream and releases any system resources
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* associated with the stream.
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* A closed <code>SequenceInputStream</code>
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* cannot perform input operations and cannot
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* be reopened.
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* <p>
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* If this stream was created
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* from an enumeration, all remaining elements
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* are requested from the enumeration and closed
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* before the <code>close</code> method returns.
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*
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* @exception IOException if an I/O error occurs.
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*/
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public void close() throws IOException {
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do {
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nextStream();
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} while (in != null);
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}
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}
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