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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.
Author: Mark Reinhold See Also: Since: JDK1.1
/**
* 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.
/**
* 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 <tt>this</tt> or a synchronized
* method.
*/
protected Object lock;
Creates a new character-stream reader whose critical sections will
synchronize on the reader itself.
/**
* 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.
Params: - lock – The Object to synchronize on.
/**
* 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.
Params: - target – the buffer to read characters into
Throws: - IOException – if an I/O error occurs
- NullPointerException – if target is null
- ReadOnlyBufferException – if target is a read only buffer
Returns: The number of characters added to the buffer, or
-1 if this source of characters is at its end Since: 1.5
/**
* 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 java.nio.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.
Throws: - IOException – If an I/O error occurs
Returns: 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
/**
* 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.
*
* <p> 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
* (<tt>0x00-0xffff</tt>), 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.
Params: - cbuf – Destination buffer
Throws: - IOException – If an I/O error occurs
Returns: The number of characters read, or -1
if the end of the stream
has been reached
/**
* 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.
Params: - cbuf – Destination buffer
- off – Offset at which to start storing characters
- len – Maximum number of characters to read
Throws: - IOException – If an I/O error occurs
Returns: The number of characters read, or -1 if the end of the
stream has been reached
/**
* 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 /** Maximum skip-buffer size */
private static final int maxSkipBufferSize = 8192;
Skip buffer, null until allocated /** 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.
Params: - n – The number of characters to skip
Throws: - IllegalArgumentException – If
n is negative. - IOException – If an I/O error occurs
Returns: The number of characters actually skipped
/**
* 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");
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.
Throws: - IOException – If an I/O error occurs
Returns: 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.
/**
* 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.
Returns: true if and only if this stream supports the mark operation.
/**
* 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.
Params: - 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 the stream does not support mark(),
or if some other I/O error occurs
/**
* 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().
Throws: - 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
/**
* 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.
Throws: - IOException – If an I/O error occurs
/**
* 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;
}