Java tutorial
/* * Copyright (c) 1996, 2015, 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 character-stream reader that allows characters to be pushed back into the * stream. * * @author Mark Reinhold * @since 1.1 */ public class PushbackReader extends FilterReader { /** Pushback buffer */ private char[] buf; /** Current position in buffer */ private int pos; /** * Creates a new pushback reader with a pushback buffer of the given size. * * @param in The reader from which characters will be read * @param size The size of the pushback buffer * @exception IllegalArgumentException if {@code size <= 0} */ public PushbackReader(Reader in, int size) { super(in); if (size <= 0) { throw new IllegalArgumentException("size <= 0"); } this.buf = new char[size]; this.pos = size; } /** * Creates a new pushback reader with a one-character pushback buffer. * * @param in The reader from which characters will be read */ public PushbackReader(Reader in) { this(in, 1); } /** Checks to make sure that the stream has not been closed. */ private void ensureOpen() throws IOException { if (buf == null) throw new IOException("Stream closed"); } /** * Reads a single character. * * @return The character read, or -1 if the end of the stream has been * reached * * @exception IOException If an I/O error occurs */ public int read() throws IOException { synchronized (lock) { ensureOpen(); if (pos < buf.length) return buf[pos++]; else return super.read(); } } /** * Reads characters into a portion of an array. * * @param cbuf Destination buffer * @param off Offset at which to start writing 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 * * @exception IOException If an I/O error occurs * @exception IndexOutOfBoundsException {@inheritDoc} */ public int read(char cbuf[], int off, int len) throws IOException { synchronized (lock) { ensureOpen(); try { if (len <= 0) { if (len < 0) { throw new IndexOutOfBoundsException(); } else if ((off < 0) || (off > cbuf.length)) { throw new IndexOutOfBoundsException(); } return 0; } int avail = buf.length - pos; if (avail > 0) { if (len < avail) avail = len; System.arraycopy(buf, pos, cbuf, off, avail); pos += avail; off += avail; len -= avail; } if (len > 0) { len = super.read(cbuf, off, len); if (len == -1) { return (avail == 0) ? -1 : avail; } return avail + len; } return avail; } catch (ArrayIndexOutOfBoundsException e) { throw new IndexOutOfBoundsException(); } } } /** * Pushes back a single character by copying it to the front of the * pushback buffer. After this method returns, the next character to be read * will have the value <code>(char)c</code>. * * @param c The int value representing a character to be pushed back * * @exception IOException If the pushback buffer is full, * or if some other I/O error occurs */ public void unread(int c) throws IOException { synchronized (lock) { ensureOpen(); if (pos == 0) throw new IOException("Pushback buffer overflow"); buf[--pos] = (char) c; } } /** * Pushes back a portion of an array of characters by copying it to the * front of the pushback buffer. After this method returns, the next * character to be read will have the value <code>cbuf[off]</code>, the * character after that will have the value <code>cbuf[off+1]</code>, and * so forth. * * @param cbuf Character array * @param off Offset of first character to push back * @param len Number of characters to push back * * @exception IOException If there is insufficient room in the pushback * buffer, or if some other I/O error occurs */ public void unread(char cbuf[], int off, int len) throws IOException { synchronized (lock) { ensureOpen(); if (len > pos) throw new IOException("Pushback buffer overflow"); pos -= len; System.arraycopy(cbuf, off, buf, pos, len); } } /** * Pushes back an array of characters by copying it to the front of the * pushback buffer. After this method returns, the next character to be * read will have the value <code>cbuf[0]</code>, the character after that * will have the value <code>cbuf[1]</code>, and so forth. * * @param cbuf Character array to push back * * @exception IOException If there is insufficient room in the pushback * buffer, or if some other I/O error occurs */ public void unread(char cbuf[]) throws IOException { unread(cbuf, 0, cbuf.length); } /** * Tells whether this stream is ready to be read. * * @exception IOException If an I/O error occurs */ public boolean ready() throws IOException { synchronized (lock) { ensureOpen(); return (pos < buf.length) || super.ready(); } } /** * Marks the present position in the stream. The <code>mark</code> * for class <code>PushbackReader</code> always throws an exception. * * @exception IOException Always, since mark is not supported */ public void mark(int readAheadLimit) throws IOException { throw new IOException("mark/reset not supported"); } /** * Resets the stream. The <code>reset</code> method of * <code>PushbackReader</code> always throws an exception. * * @exception IOException Always, since reset is not supported */ public void reset() throws IOException { throw new IOException("mark/reset not supported"); } /** * Tells whether this stream supports the mark() operation, which it does * not. */ public boolean markSupported() { return false; } /** * Closes the stream and releases any system resources associated with * it. Once the stream has been closed, further read(), * unread(), ready(), or skip() invocations will throw an IOException. * Closing a previously closed stream has no effect. This method will block * while there is another thread blocking on the reader. * * @exception IOException If an I/O error occurs */ public void close() throws IOException { synchronized (lock) { super.close(); buf = null; } } /** * Skips characters. This method will block until some characters are * available, an I/O error occurs, or the end of the stream is reached. * * @param n The number of characters to skip * * @return The number of characters actually skipped * * @exception IllegalArgumentException If <code>n</code> is negative. * @exception 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(); int avail = buf.length - pos; if (avail > 0) { if (n <= avail) { pos += n; return n; } else { pos = buf.length; n -= avail; } } return avail + super.skip(n); } } }