Java tutorial
/* * 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 * or visit www.oracle.com if you need additional information or have any * questions. */ package java.io; /** * A buffered character-input stream that keeps track of line numbers. This * class defines methods {@link #setLineNumber(int)} and {@link * #getLineNumber()} for setting and getting the current line number * respectively. * * <p> By default, line numbering begins at 0. This number increments at every * <a href="#lt">line terminator</a> as the data is read, and can be changed * with a call to {@code setLineNumber(int)}. Note however, that * {@code setLineNumber(int)} does not actually change the current position in * the stream; it only changes the value that will be returned by * {@code getLineNumber()}. * * <p> A line is considered to be <a id="lt">terminated</a> by any one of a * line feed ('\n'), a carriage return ('\r'), or a carriage return followed * immediately by a linefeed. * * @author Mark Reinhold * @since 1.1 */ public class LineNumberReader extends BufferedReader { /** The current line number */ private int lineNumber = 0; /** The line number of the mark, if any */ private int markedLineNumber; // Defaults to 0 /** If the next character is a line feed, skip it */ private boolean skipLF; /** The skipLF flag when the mark was set */ private boolean markedSkipLF; /** * Create a new line-numbering reader, using the default input-buffer * size. * * @param in * A Reader object to provide the underlying stream */ public LineNumberReader(Reader in) { super(in); } /** * Create a new line-numbering reader, reading characters into a buffer of * the given size. * * @param in * A Reader object to provide the underlying stream * * @param sz * An int specifying the size of the buffer */ public LineNumberReader(Reader in, int sz) { super(in, sz); } /** * Set the current line number. * * @param lineNumber * An int specifying the line number * * @see #getLineNumber */ public void setLineNumber(int lineNumber) { this.lineNumber = lineNumber; } /** * Get the current line number. * * @return The current line number * * @see #setLineNumber */ public int getLineNumber() { return lineNumber; } /** * Read a single character. <a href="#lt">Line terminators</a> are * compressed into single newline ('\n') characters. Whenever a line * terminator is read the current line number is incremented. * * @return The character read, or -1 if the end of the stream has been * reached * * @throws IOException * If an I/O error occurs */ @SuppressWarnings("fallthrough") public int read() throws IOException { synchronized (lock) { int c = super.read(); if (skipLF) { if (c == '\n') c = super.read(); skipLF = false; } switch (c) { case '\r': skipLF = true; case '\n': /* Fall through */ lineNumber++; return '\n'; } return c; } } /** * Read characters into a portion of an array. Whenever a <a * href="#lt">line terminator</a> is read the current line number is * incremented. * * @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 bytes read, or -1 if the end of the stream has * already been reached * * @throws IOException * If an I/O error occurs * * @throws IndexOutOfBoundsException {@inheritDoc} */ @SuppressWarnings("fallthrough") public int read(char cbuf[], int off, int len) throws IOException { synchronized (lock) { int n = super.read(cbuf, off, len); for (int i = off; i < off + n; i++) { int c = cbuf[i]; if (skipLF) { skipLF = false; if (c == '\n') continue; } switch (c) { case '\r': skipLF = true; case '\n': /* Fall through */ lineNumber++; break; } } return n; } } /** * Read a line of text. Whenever a <a href="#lt">line terminator</a> is * read the current line number is incremented. * * @return A String containing the contents of the line, not including * any <a href="#lt">line termination characters</a>, or * {@code null} if the end of the stream has been reached * * @throws IOException * If an I/O error occurs */ public String readLine() throws IOException { synchronized (lock) { String l = super.readLine(skipLF); skipLF = false; if (l != null) lineNumber++; return l; } } /** Maximum skip-buffer size */ private static final int maxSkipBufferSize = 8192; /** Skip buffer, null until allocated */ private char skipBuffer[] = null; /** * Skip characters. * * @param n * The number of characters to skip * * @return The number of characters actually skipped * * @throws IOException * If an I/O error occurs * * @throws IllegalArgumentException * If {@code n} is negative */ public long skip(long n) throws IOException { if (n < 0) throw new IllegalArgumentException("skip() value is negative"); int nn = (int) Math.min(n, maxSkipBufferSize); synchronized (lock) { if ((skipBuffer == null) || (skipBuffer.length < nn)) skipBuffer = new char[nn]; long r = n; while (r > 0) { int nc = read(skipBuffer, 0, (int) Math.min(r, nn)); if (nc == -1) break; r -= nc; } return n - r; } } /** * Mark the present position in the stream. Subsequent calls to reset() * will attempt to reposition the stream to this point, and will also reset * the line number appropriately. * * @param readAheadLimit * Limit on the number of characters that may be read while still * preserving the mark. After reading this many characters, * attempting to reset the stream may fail. * * @throws IOException * If an I/O error occurs */ public void mark(int readAheadLimit) throws IOException { synchronized (lock) { // If the most recently read character is '\r', then increment the // read ahead limit as in this case if the next character is '\n', // two characters would actually be read by the next read(). if (skipLF) readAheadLimit++; super.mark(readAheadLimit); markedLineNumber = lineNumber; markedSkipLF = skipLF; } } /** * Reset the stream to the most recent mark. * * @throws IOException * If the stream has not been marked, or if the mark has been * invalidated */ public void reset() throws IOException { synchronized (lock) { super.reset(); lineNumber = markedLineNumber; skipLF = markedSkipLF; } } }