java.io.Reader Maven / Gradle / Ivy
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* 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).
*
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*
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package java.io;
/**
* Abstract class for reading character streams. The only methods that a
* subclass must implement are read(char[], int, int) and close(). Most
* subclasses, however, will override some of the methods defined here in order
* to provide higher efficiency, additional functionality, or both.
*
*
* @see BufferedReader
* @see LineNumberReader
* @see CharArrayReader
* @see InputStreamReader
* @see FileReader
* @see FilterReader
* @see PushbackReader
* @see PipedReader
* @see StringReader
* @see Writer
*
* @author Mark Reinhold
* @since JDK1.1
*/
public abstract class Reader implements Readable, Closeable {
/**
* The object used to synchronize operations on this stream. For
* efficiency, a character-stream object may use an object other than
* itself to protect critical sections. A subclass should therefore use
* the object in this field rather than this or a synchronized
* method.
*/
protected Object lock;
/**
* Creates a new character-stream reader whose critical sections will
* synchronize on the reader itself.
*/
protected Reader() {
this.lock = this;
}
/**
* Creates a new character-stream reader whose critical sections will
* synchronize on the given object.
*
* @param lock The Object to synchronize on.
*/
protected Reader(Object lock) {
if (lock == null) {
throw new NullPointerException();
}
this.lock = lock;
}
/**
* Attempts to read characters into the specified character buffer.
* The buffer is used as a repository of characters as-is: the only
* changes made are the results of a put operation. No flipping or
* rewinding of the buffer is performed.
*
* @param target the buffer to read characters into
* @return The number of characters added to the buffer, or
* -1 if this source of characters is at its end
* @throws IOException if an I/O error occurs
* @throws NullPointerException if target is null
* @throws ReadOnlyBufferException if target is a read only buffer
* @since 1.5
*/
// public int read(java.nio.CharBuffer target) throws IOException {
// int len = target.remaining();
// char[] cbuf = new char[len];
// int n = read(cbuf, 0, len);
// if (n > 0)
// target.put(cbuf, 0, n);
// return n;
// }
/**
* Reads a single character. This method will block until a character is
* available, an I/O error occurs, or the end of the stream is reached.
*
* Subclasses that intend to support efficient single-character input
* should override this method.
*
* @return 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
*
* @exception IOException If an I/O error occurs
*/
public int read() throws IOException {
char cb[] = new char[1];
if (read(cb, 0, 1) == -1)
return -1;
else
return cb[0];
}
/**
* Reads characters into an array. This method will block until some input
* is available, an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer
*
* @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[]) throws IOException {
return read(cbuf, 0, cbuf.length);
}
/**
* Reads characters into a portion of an array. This method will block
* until some input is available, an I/O error occurs, or the end of the
* stream is reached.
*
* @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
*
* @exception IOException If an I/O error occurs
*/
abstract public int read(char cbuf[], int off, int len) throws IOException;
/** Maximum skip-buffer size */
private static final int maxSkipBufferSize = 8192;
/** Skip buffer, null until allocated */
private char skipBuffer[] = 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 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");
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;
}
}
/**
* Tells whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input,
* false otherwise. Note that returning false does not guarantee that the
* next read will block.
*
* @exception IOException If an I/O error occurs
*/
public boolean ready() throws IOException {
return false;
}
/**
* Tells whether this stream supports the mark() operation. The default
* implementation always returns false. Subclasses should override this
* method.
*
* @return true if and only if this stream supports the mark operation.
*/
public boolean markSupported() {
return false;
}
/**
* Marks the present position in the stream. Subsequent calls to reset()
* will attempt to reposition the stream to this point. Not all
* character-input streams support the mark() operation.
*
* @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.
*
* @exception IOException If the stream does not support mark(),
* or if some other I/O error occurs
*/
public void mark(int readAheadLimit) throws IOException {
throw new IOException("mark() not supported");
}
/**
* Resets the stream. If the stream has been marked, then attempt to
* reposition it at the mark. If the stream has not been marked, then
* attempt to reset it in some way appropriate to the particular stream,
* for example by repositioning it to its starting point. Not all
* character-input streams support the reset() operation, and some support
* reset() without supporting mark().
*
* @exception IOException If the stream has not been marked,
* or if the mark has been invalidated,
* or if the stream does not support reset(),
* or if some other I/O error occurs
*/
public void reset() throws IOException {
throw new IOException("reset() not supported");
}
/**
* 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.
*
* @exception IOException If an I/O error occurs
*/
abstract public void close() throws IOException;
}