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; /** * This class implements a character buffer that can be used as a * character-input stream. * * @author Herb Jellinek * @since 1.1 */ public class CharArrayReader extends Reader { /** The character buffer. */ protected char buf[]; /** The current buffer position. */ protected int pos; /** The position of mark in buffer. */ protected int markedPos = 0; /** * The index of the end of this buffer. There is not valid * data at or beyond this index. */ protected int count; /** * Creates a CharArrayReader from the specified array of chars. * @param buf Input buffer (not copied) */ public CharArrayReader(char buf[]) { this.buf = buf; this.pos = 0; this.count = buf.length; } /** * Creates a CharArrayReader from the specified array of chars. * * <p> The resulting reader will start reading at the given * {@code offset}. The total number of {@code char} values that can be * read from this reader will be either {@code length} or * {@code buf.length-offset}, whichever is smaller. * * @throws IllegalArgumentException * If {@code offset} is negative or greater than * {@code buf.length}, or if {@code length} is negative, or if * the sum of these two values is negative. * * @param buf Input buffer (not copied) * @param offset Offset of the first char to read * @param length Number of chars to read */ public CharArrayReader(char buf[], int offset, int length) { if ((offset < 0) || (offset > buf.length) || (length < 0) || ((offset + length) < 0)) { throw new IllegalArgumentException(); } this.buf = buf; this.pos = offset; this.count = Math.min(offset + length, buf.length); this.markedPos = offset; } /** 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. * * @exception IOException If an I/O error occurs */ public int read() throws IOException { synchronized (lock) { ensureOpen(); if (pos >= count) return -1; else return buf[pos++]; } } /** * Reads characters into a portion of an array. * @param b Destination buffer * @param off Offset at which to start storing characters * @param len Maximum number of characters to read * @return The actual 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 b[], int off, int len) throws IOException { synchronized (lock) { ensureOpen(); if ((off < 0) || (off > b.length) || (len < 0) || ((off + len) > b.length) || ((off + len) < 0)) { throw new IndexOutOfBoundsException(); } else if (len == 0) { return 0; } if (pos >= count) { return -1; } int avail = count - pos; if (len > avail) { len = avail; } if (len <= 0) { return 0; } System.arraycopy(buf, pos, b, off, len); pos += len; return len; } } /** * Skips characters. Returns the number of characters that were skipped. * * <p>The <code>n</code> parameter may be negative, even though the * <code>skip</code> method of the {@link Reader} superclass throws * an exception in this case. If <code>n</code> is negative, then * this method does nothing and returns <code>0</code>. * * @param n The number of characters to skip * @return The number of characters actually skipped * @exception IOException If the stream is closed, or an I/O error occurs */ public long skip(long n) throws IOException { synchronized (lock) { ensureOpen(); long avail = count - pos; if (n > avail) { n = avail; } if (n < 0) { return 0; } pos += n; return n; } } /** * Tells whether this stream is ready to be read. Character-array readers * are always ready to be read. * * @exception IOException If an I/O error occurs */ public boolean ready() throws IOException { synchronized (lock) { ensureOpen(); return (count - pos) > 0; } } /** * 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 reposition the stream to this point. * * @param readAheadLimit Limit on the number of characters that may be * read while still preserving the mark. Because * the stream's input comes from a character array, * there is no actual limit; hence this argument is * ignored. * * @exception IOException If an I/O error occurs */ public void mark(int readAheadLimit) throws IOException { synchronized (lock) { ensureOpen(); markedPos = pos; } } /** * Resets the stream to the most recent mark, or to the beginning if it has * never been marked. * * @exception IOException If an I/O error occurs */ public void reset() throws IOException { synchronized (lock) { ensureOpen(); pos = markedPos; } } /** * Closes the stream and releases any system resources associated with * it. Once the stream has been closed, further read(), ready(), * mark(), reset(), 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. */ public void close() { synchronized (lock) { buf = null; } } }