Java example source code file (PushbackReader.java)
The PushbackReader.java Java example source code/*
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* 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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*/
package java.io;
/**
* A character-stream reader that allows characters to be pushed back into the
* stream.
*
* @author Mark Reinhold
* @since JDK1.1
*/
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
*/
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.
*
* @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], the
* character after that will have the value <code>cbuf[off+1], 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], the character after that
* will have the value <code>cbuf[1], 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
* for class <code>PushbackReader 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 method of
* <code>PushbackReader 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.
*
* @exception IOException If an I/O error occurs
*/
public void close() throws IOException {
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 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);
}
}
}
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