https://openjdk.java.net/ 
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 * Copyright (c) 1996, 2019, 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
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 * questions.
 */

package java.io;


import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;


Reads text from a character-input stream, buffering characters so as to
provide for the efficient reading of characters, arrays, and lines.

 The buffer size may be specified, or the default size may be used.  The
default is large enough for most purposes.

 In general, each read request made of a Reader causes a corresponding
read request to be made of the underlying character or byte stream.  It is
therefore advisable to wrap a BufferedReader around any Reader whose read()
operations may be costly, such as FileReaders and InputStreamReaders.  For
example,

BufferedReader in
  = new BufferedReader(new FileReader("foo.in"));


will buffer the input from the specified file.  Without buffering, each
invocation of read() or readLine() could cause bytes to be read from the
file, converted into characters, and then returned, which can be very
inefficient.

 Programs that use DataInputStreams for textual input can be localized by
replacing each DataInputStream with an appropriate BufferedReader.

Author:     Mark Reinhold
See Also:
Since:      1.1
/**
 * Reads text from a character-input stream, buffering characters so as to
 * provide for the efficient reading of characters, arrays, and lines.
 *
 * <p> The buffer size may be specified, or the default size may be used.  The
 * default is large enough for most purposes.
 *
 * <p> In general, each read request made of a Reader causes a corresponding
 * read request to be made of the underlying character or byte stream.  It is
 * therefore advisable to wrap a BufferedReader around any Reader whose read()
 * operations may be costly, such as FileReaders and InputStreamReaders.  For
 * example,
 *
 * <pre>
 * BufferedReader in
 *   = new BufferedReader(new FileReader("foo.in"));
 * </pre>
 *
 * will buffer the input from the specified file.  Without buffering, each
 * invocation of read() or readLine() could cause bytes to be read from the
 * file, converted into characters, and then returned, which can be very
 * inefficient.
 *
 * <p> Programs that use DataInputStreams for textual input can be localized by
 * replacing each DataInputStream with an appropriate BufferedReader.
 *
 * @see FileReader
 * @see InputStreamReader
 * @see java.nio.file.Files#newBufferedReader
 *
 * @author      Mark Reinhold
 * @since       1.1
 */

public class BufferedReader extends Reader {

    private Reader in;

    private char cb[];
    private int nChars, nextChar;

    private static final int INVALIDATED = -2;
    private static final int UNMARKED = -1;
    private int markedChar = UNMARKED;
    private int readAheadLimit = 0; /* Valid only when markedChar > 0 */

    
If the next character is a line feed, skip it 
/** If the next character is a line feed, skip it */
    private boolean skipLF = false;

    
The skipLF flag when the mark was set 
/** The skipLF flag when the mark was set */
    private boolean markedSkipLF = false;

    private static int defaultCharBufferSize = 8192;
    private static int defaultExpectedLineLength = 80;

    
Creates a buffering character-input stream that uses an input buffer of
the specified size.

Params:
  • in –   A Reader
  • sz –   Input-buffer size
Throws:
/**
     * Creates a buffering character-input stream that uses an input buffer of
     * the specified size.
     *
     * @param  in   A Reader
     * @param  sz   Input-buffer size
     *
     * @throws IllegalArgumentException  If {@code sz <= 0}
     */
    public BufferedReader(Reader in, int sz) {
        super(in);
        if (sz <= 0)
            throw new IllegalArgumentException("Buffer size <= 0");
        this.in = in;
        cb = new char[sz];
        nextChar = nChars = 0;
    }

    
Creates a buffering character-input stream that uses a default-sized
input buffer.

Params:
  • in –   A Reader
/**
     * Creates a buffering character-input stream that uses a default-sized
     * input buffer.
     *
     * @param  in   A Reader
     */
    public BufferedReader(Reader in) {
        this(in, defaultCharBufferSize);
    }

    
Checks to make sure that the stream has not been closed 
/** Checks to make sure that the stream has not been closed */
    private void ensureOpen() throws IOException {
        if (in == null)
            throw new IOException("Stream closed");
    }

    
Fills the input buffer, taking the mark into account if it is valid.

/**
     * Fills the input buffer, taking the mark into account if it is valid.
     */
    private void fill() throws IOException {
        int dst;
        if (markedChar <= UNMARKED) {
            /* No mark */
            dst = 0;
        } else {
            /* Marked */
            int delta = nextChar - markedChar;
            if (delta >= readAheadLimit) {
                /* Gone past read-ahead limit: Invalidate mark */
                markedChar = INVALIDATED;
                readAheadLimit = 0;
                dst = 0;
            } else {
                if (readAheadLimit <= cb.length) {
                    /* Shuffle in the current buffer */
                    System.arraycopy(cb, markedChar, cb, 0, delta);
                    markedChar = 0;
                    dst = delta;
                } else {
                    /* Reallocate buffer to accommodate read-ahead limit */
                    char ncb[] = new char[readAheadLimit];
                    System.arraycopy(cb, markedChar, ncb, 0, delta);
                    cb = ncb;
                    markedChar = 0;
                    dst = delta;
                }
                nextChar = nChars = delta;
            }
        }

        int n;
        do {
            n = in.read(cb, dst, cb.length - dst);
        } while (n == 0);
        if (n > 0) {
            nChars = dst + n;
            nextChar = dst;
        }
    }

    
Reads a single character.

Throws:
Returns:The character read, as an integer in the range 0 to 65535 (0x00-0xffff), or -1 if the end of the stream has been reached
/**
     * Reads a single character.
     *
     * @return The character read, as an integer in the range
     *         0 to 65535 ({@code 0x00-0xffff}), or -1 if the
     *         end of the stream has been reached
     * @throws     IOException  If an I/O error occurs
     */
    public int read() throws IOException {
        synchronized (lock) {
            ensureOpen();
            for (;;) {
                if (nextChar >= nChars) {
                    fill();
                    if (nextChar >= nChars)
                        return -1;
                }
                if (skipLF) {
                    skipLF = false;
                    if (cb[nextChar] == '\n') {
                        nextChar++;
                        continue;
                    }
                }
                return cb[nextChar++];
            }
        }
    }

    
Reads characters into a portion of an array, reading from the underlying
stream if necessary.

/**
     * Reads characters into a portion of an array, reading from the underlying
     * stream if necessary.
     */
    private int read1(char[] cbuf, int off, int len) throws IOException {
        if (nextChar >= nChars) {
            /* If the requested length is at least as large as the buffer, and
               if there is no mark/reset activity, and if line feeds are not
               being skipped, do not bother to copy the characters into the
               local buffer.  In this way buffered streams will cascade
               harmlessly. */
            if (len >= cb.length && markedChar <= UNMARKED && !skipLF) {
                return in.read(cbuf, off, len);
            }
            fill();
        }
        if (nextChar >= nChars) return -1;
        if (skipLF) {
            skipLF = false;
            if (cb[nextChar] == '\n') {
                nextChar++;
                if (nextChar >= nChars)
                    fill();
                if (nextChar >= nChars)
                    return -1;
            }
        }
        int n = Math.min(len, nChars - nextChar);
        System.arraycopy(cb, nextChar, cbuf, off, n);
        nextChar += n;
        return n;
    }

    
Reads characters into a portion of an array.

 This method implements the general contract of the corresponding
read method of the
Reader class. As an additional convenience, it attempts to read as many characters as possible by repeatedly invoking the read method of the underlying stream. This iterated read continues until one of the following conditions becomes true: 
    
  
  •  The specified number of characters have been read,
  
  •  The read method of the underlying stream returns -1, indicating end-of-file, or 
  •  The ready method of the underlying stream returns false, indicating that further input requests would block. 
 If the first read on the underlying stream returns -1 to indicate end-of-file then this method returns -1. Otherwise this method returns the number of characters actually read. 
 Subclasses of this class are encouraged, but not required, to
attempt to read as many characters as possible in the same fashion.

 Ordinarily this method takes characters from this stream's character buffer, filling it from the underlying stream as necessary. If, however, the buffer is empty, the mark is not valid, and the requested length is at least as large as the buffer, then this method will read characters directly from the underlying stream into the given array. Thus redundant BufferedReaders will not copy data unnecessarily. 
Params:
  • cbuf –  Destination buffer
  • off –   Offset at which to start storing characters
  • len –   Maximum number of characters to read
Throws:
Returns:    The number of characters read, or -1 if the end of the
            stream has been reached
/**
     * Reads characters into a portion of an array.
     *
     * <p> This method implements the general contract of the corresponding
     * <code>{@link Reader#read(char[], int, int) read}</code> method of the
     * <code>{@link Reader}</code> class.  As an additional convenience, it
     * attempts to read as many characters as possible by repeatedly invoking
     * the {@code read} method of the underlying stream.  This iterated
     * {@code read} continues until one of the following conditions becomes
     * true: <ul>
     *
     *   <li> The specified number of characters have been read,
     *
     *   <li> The {@code read} method of the underlying stream returns
     *   {@code -1}, indicating end-of-file, or
     *
     *   <li> The {@code ready} method of the underlying stream
     *   returns {@code false}, indicating that further input requests
     *   would block.
     *
     * </ul> If the first {@code read} on the underlying stream returns
     * {@code -1} to indicate end-of-file then this method returns
     * {@code -1}.  Otherwise this method returns the number of characters
     * actually read.
     *
     * <p> Subclasses of this class are encouraged, but not required, to
     * attempt to read as many characters as possible in the same fashion.
     *
     * <p> Ordinarily this method takes characters from this stream's character
     * buffer, filling it from the underlying stream as necessary.  If,
     * however, the buffer is empty, the mark is not valid, and the requested
     * length is at least as large as the buffer, then this method will read
     * characters directly from the underlying stream into the given array.
     * Thus redundant {@code BufferedReader}s will not copy data
     * unnecessarily.
     *
     * @param      cbuf  Destination buffer
     * @param      off   Offset at which to start storing characters
     * @param      len   Maximum number of characters to read
     *
     * @return     The number of characters read, or -1 if the end of the
     *             stream has been reached
     *
     * @throws     IOException  If an I/O error occurs
     * @throws     IndexOutOfBoundsException {@inheritDoc}
     */
    public int read(char cbuf[], int off, int len) throws IOException {
        synchronized (lock) {
            ensureOpen();
            if ((off < 0) || (off > cbuf.length) || (len < 0) ||
                ((off + len) > cbuf.length) || ((off + len) < 0)) {
                throw new IndexOutOfBoundsException();
            } else if (len == 0) {
                return 0;
            }

            int n = read1(cbuf, off, len);
            if (n <= 0) return n;
            while ((n < len) && in.ready()) {
                int n1 = read1(cbuf, off + n, len - n);
                if (n1 <= 0) break;
                n += n1;
            }
            return n;
        }
    }

    
Reads a line of text.  A line is considered to be terminated by any one
of a line feed ('\n'), a carriage return ('\r'), a carriage return
followed immediately by a line feed, or by reaching the end-of-file
(EOF).

Params:
  • ignoreLF –  If true, the next '\n' will be skipped
Throws:
See Also:
Returns:    A String containing the contents of the line, not including
            any line-termination characters, or null if the end of the
            stream has been reached without reading any characters
/**
     * Reads a line of text.  A line is considered to be terminated by any one
     * of a line feed ('\n'), a carriage return ('\r'), a carriage return
     * followed immediately by a line feed, or by reaching the end-of-file
     * (EOF).
     *
     * @param      ignoreLF  If true, the next '\n' will be skipped
     *
     * @return     A String containing the contents of the line, not including
     *             any line-termination characters, or null if the end of the
     *             stream has been reached without reading any characters
     *
     * @see        java.io.LineNumberReader#readLine()
     *
     * @throws     IOException  If an I/O error occurs
     */
    String readLine(boolean ignoreLF) throws IOException {
        StringBuilder s = null;
        int startChar;

        synchronized (lock) {
            ensureOpen();
            boolean omitLF = ignoreLF || skipLF;

        bufferLoop:
            for (;;) {

                if (nextChar >= nChars)
                    fill();
                if (nextChar >= nChars) { /* EOF */
                    if (s != null && s.length() > 0)
                        return s.toString();
                    else
                        return null;
                }
                boolean eol = false;
                char c = 0;
                int i;

                /* Skip a leftover '\n', if necessary */
                if (omitLF && (cb[nextChar] == '\n'))
                    nextChar++;
                skipLF = false;
                omitLF = false;

            charLoop:
                for (i = nextChar; i < nChars; i++) {
                    c = cb[i];
                    if ((c == '\n') || (c == '\r')) {
                        eol = true;
                        break charLoop;
                    }
                }

                startChar = nextChar;
                nextChar = i;

                if (eol) {
                    String str;
                    if (s == null) {
                        str = new String(cb, startChar, i - startChar);
                    } else {
                        s.append(cb, startChar, i - startChar);
                        str = s.toString();
                    }
                    nextChar++;
                    if (c == '\r') {
                        skipLF = true;
                    }
                    return str;
                }

                if (s == null)
                    s = new StringBuilder(defaultExpectedLineLength);
                s.append(cb, startChar, i - startChar);
            }
        }
    }

    
Reads a line of text.  A line is considered to be terminated by any one
of a line feed ('\n'), a carriage return ('\r'), a carriage return
followed immediately by a line feed, or by reaching the end-of-file
(EOF).

Throws:
See Also:
Returns:    A String containing the contents of the line, not including
            any line-termination characters, or null if the end of the
            stream has been reached without reading any characters
/**
     * Reads a line of text.  A line is considered to be terminated by any one
     * of a line feed ('\n'), a carriage return ('\r'), a carriage return
     * followed immediately by a line feed, or by reaching the end-of-file
     * (EOF).
     *
     * @return     A String containing the contents of the line, not including
     *             any line-termination characters, or null if the end of the
     *             stream has been reached without reading any characters
     *
     * @throws     IOException  If an I/O error occurs
     *
     * @see java.nio.file.Files#readAllLines
     */
    public String readLine() throws IOException {
        return readLine(false);
    }

    
Skips characters.

Params:
  • n –  The number of characters to skip
Throws:
Returns:   The number of characters actually skipped
/**
     * Skips characters.
     *
     * @param  n  The number of characters to skip
     *
     * @return    The number of characters actually skipped
     *
     * @throws     IllegalArgumentException  If {@code n} is negative.
     * @throws     IOException  If an I/O error occurs
     */
    public long skip(long n) throws IOException {
        if (n < 0L) {
            throw new IllegalArgumentException("skip value is negative");
        }
        synchronized (lock) {
            ensureOpen();
            long r = n;
            while (r > 0) {
                if (nextChar >= nChars)
                    fill();
                if (nextChar >= nChars) /* EOF */
                    break;
                if (skipLF) {
                    skipLF = false;
                    if (cb[nextChar] == '\n') {
                        nextChar++;
                    }
                }
                long d = nChars - nextChar;
                if (r <= d) {
                    nextChar += r;
                    r = 0;
                    break;
                }
                else {
                    r -= d;
                    nextChar = nChars;
                }
            }
            return n - r;
        }
    }

    
Tells whether this stream is ready to be read.  A buffered character
stream is ready if the buffer is not empty, or if the underlying
character stream is ready.

Throws:
  • IOException –  If an I/O error occurs
/**
     * Tells whether this stream is ready to be read.  A buffered character
     * stream is ready if the buffer is not empty, or if the underlying
     * character stream is ready.
     *
     * @throws     IOException  If an I/O error occurs
     */
    public boolean ready() throws IOException {
        synchronized (lock) {
            ensureOpen();

            /*
             * If newline needs to be skipped and the next char to be read
             * is a newline character, then just skip it right away.
             */
            if (skipLF) {
                /* Note that in.ready() will return true if and only if the next
                 * read on the stream will not block.
                 */
                if (nextChar >= nChars && in.ready()) {
                    fill();
                }
                if (nextChar < nChars) {
                    if (cb[nextChar] == '\n')
                        nextChar++;
                    skipLF = false;
                }
            }
            return (nextChar < nChars) || in.ready();
        }
    }

    
Tells whether this stream supports the mark() operation, which it does.

/**
     * Tells whether this stream supports the mark() operation, which it does.
     */
    public boolean markSupported() {
        return true;
    }

    
Marks the present position in the stream.  Subsequent calls to reset()
will attempt to reposition the stream to this point.

Params:
  • readAheadLimit –   Limit on the number of characters that may be
                        read while still preserving the mark. An attempt
                        to reset the stream after reading characters
                        up to this limit or beyond may fail.
                        A limit value larger than the size of the input
                        buffer will cause a new buffer to be allocated
                        whose size is no smaller than limit.
                        Therefore large values should be used with care.
Throws:
/**
     * Marks the present position in the stream.  Subsequent calls to reset()
     * will attempt to reposition the stream to this point.
     *
     * @param readAheadLimit   Limit on the number of characters that may be
     *                         read while still preserving the mark. An attempt
     *                         to reset the stream after reading characters
     *                         up to this limit or beyond may fail.
     *                         A limit value larger than the size of the input
     *                         buffer will cause a new buffer to be allocated
     *                         whose size is no smaller than limit.
     *                         Therefore large values should be used with care.
     *
     * @throws     IllegalArgumentException  If {@code readAheadLimit < 0}
     * @throws     IOException  If an I/O error occurs
     */
    public void mark(int readAheadLimit) throws IOException {
        if (readAheadLimit < 0) {
            throw new IllegalArgumentException("Read-ahead limit < 0");
        }
        synchronized (lock) {
            ensureOpen();
            this.readAheadLimit = readAheadLimit;
            markedChar = nextChar;
            markedSkipLF = skipLF;
        }
    }

    
Resets the stream to the most recent mark.

Throws:
  • IOException –  If the stream has never been marked,
                         or if the mark has been invalidated
/**
     * Resets the stream to the most recent mark.
     *
     * @throws     IOException  If the stream has never been marked,
     *                          or if the mark has been invalidated
     */
    public void reset() throws IOException {
        synchronized (lock) {
            ensureOpen();
            if (markedChar < 0)
                throw new IOException((markedChar == INVALIDATED)
                                      ? "Mark invalid"
                                      : "Stream not marked");
            nextChar = markedChar;
            skipLF = markedSkipLF;
        }
    }

    public void close() throws IOException {
        synchronized (lock) {
            if (in == null)
                return;
            try {
                in.close();
            } finally {
                in = null;
                cb = null;
            }
        }
    }

    
Returns a Stream, the elements of which are lines read from this BufferedReader. The Stream is lazily populated, i.e., read only occurs during the terminal
stream operation.

 The reader must not be operated on during the execution of the
terminal stream operation. Otherwise, the result of the terminal stream
operation is undefined.

 After execution of the terminal stream operation there are no
guarantees that the reader will be at a specific position from which to
read the next character or line.

 If an IOException is thrown when accessing the underlying BufferedReader, it is wrapped in an UncheckedIOException which will be thrown from the Stream method that caused the read to take place. This method will return a Stream if invoked on a BufferedReader that is closed. Any operation on that stream that requires reading from the BufferedReader after it is closed, will cause an UncheckedIOException to be thrown. 
Returns:a Stream<String> providing the lines of text described by this BufferedReader
Since:1.8
/**
     * Returns a {@code Stream}, the elements of which are lines read from
     * this {@code BufferedReader}.  The {@link Stream} is lazily populated,
     * i.e., read only occurs during the
     * <a href="../util/stream/package-summary.html#StreamOps">terminal
     * stream operation</a>.
     *
     * <p> The reader must not be operated on during the execution of the
     * terminal stream operation. Otherwise, the result of the terminal stream
     * operation is undefined.
     *
     * <p> After execution of the terminal stream operation there are no
     * guarantees that the reader will be at a specific position from which to
     * read the next character or line.
     *
     * <p> If an {@link IOException} is thrown when accessing the underlying
     * {@code BufferedReader}, it is wrapped in an {@link
     * UncheckedIOException} which will be thrown from the {@code Stream}
     * method that caused the read to take place. This method will return a
     * Stream if invoked on a BufferedReader that is closed. Any operation on
     * that stream that requires reading from the BufferedReader after it is
     * closed, will cause an UncheckedIOException to be thrown.
     *
     * @return a {@code Stream<String>} providing the lines of text
     *         described by this {@code BufferedReader}
     *
     * @since 1.8
     */
    public Stream<String> lines() {
        Iterator<String> iter = new Iterator<>() {
            String nextLine = null;

            @Override
            public boolean hasNext() {
                if (nextLine != null) {
                    return true;
                } else {
                    try {
                        nextLine = readLine();
                        return (nextLine != null);
                    } catch (IOException e) {
                        throw new UncheckedIOException(e);
                    }
                }
            }

            @Override
            public String next() {
                if (nextLine != null || hasNext()) {
                    String line = nextLine;
                    nextLine = null;
                    return line;
                } else {
                    throw new NoSuchElementException();
                }
            }
        };
        return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
                iter, Spliterator.ORDERED | Spliterator.NONNULL), false);
    }
}