Reader
public
abstract
class
Reader
extends Object
implements
Readable,
Closeable
java.lang.Object | |
↳ | java.io.Reader |
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 also:
Summary
Fields | |
---|---|
protected
Object |
lock
The object used to synchronize operations on this stream. |
Protected constructors | |
---|---|
Reader()
Creates a new character-stream reader whose critical sections will synchronize on the reader itself. |
|
Reader(Object lock)
Creates a new character-stream reader whose critical sections will synchronize on the given object. |
Public methods | |
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abstract
void
|
close()
Closes the stream and releases any system resources associated with it. |
void
|
mark(int readAheadLimit)
Marks the present position in the stream. |
boolean
|
markSupported()
Tells whether this stream supports the mark() operation. |
static
Reader
|
nullReader()
Returns a new |
int
|
read()
Reads a single character. |
abstract
int
|
read(char[] cbuf, int off, int len)
Reads characters into a portion of an array. |
int
|
read(char[] cbuf)
Reads characters into an array. |
int
|
read(CharBuffer target)
Attempts to read characters into the specified character buffer. |
boolean
|
ready()
Tells whether this stream is ready to be read. |
void
|
reset()
Resets the stream. |
long
|
skip(long n)
Skips characters. |
long
|
transferTo(Writer out)
Reads all characters from this reader and writes the characters to the given writer in the order that they are read. |
Inherited methods | |
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Fields
lock
protected Object lock
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 constructors
Reader
protected Reader ()
Creates a new character-stream reader whose critical sections will synchronize on the reader itself.
Reader
protected Reader (Object lock)
Creates a new character-stream reader whose critical sections will synchronize on the given object.
Parameters | |
---|---|
lock |
Object : The Object to synchronize on. |
Public methods
close
public abstract void close ()
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 |
mark
public void mark (int readAheadLimit)
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.
Parameters | |
---|---|
readAheadLimit |
int : 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 |
markSupported
public boolean markSupported ()
Tells whether this stream supports the mark() operation. The default implementation always returns false. Subclasses should override this method.
Returns | |
---|---|
boolean |
true if and only if this stream supports the mark operation. |
nullReader
public static Reader nullReader ()
Returns a new Reader
that reads no characters. The returned
stream is initially open. The stream is closed by calling the
close()
method. Subsequent calls to close()
have no
effect.
While the stream is open, the read()
, read(char[])
,
read(char[], int, int)
, read(Charbuffer)
, ready()
, skip(long)
, and transferTo()
methods all
behave as if end of stream has been reached. After the stream has been
closed, these methods all throw IOException
.
The markSupported()
method returns false
. The
mark()
and reset()
methods throw an IOException
.
The object
used to synchronize operations on the
returned Reader
is not specified.
Returns | |
---|---|
Reader |
a Reader which reads no characters |
read
public int read ()
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.
Returns | |
---|---|
int |
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 |
Throws | |
---|---|
IOException |
If an I/O error occurs |
read
public abstract int read (char[] cbuf, int off, int len)
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.
Parameters | |
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cbuf |
char : Destination buffer |
off |
int : Offset at which to start storing characters |
len |
int : Maximum number of characters to read |
Returns | |
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int |
The number of characters read, or -1 if the end of the stream has been reached |
Throws | |
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IOException |
If an I/O error occurs |
IndexOutOfBoundsException |
If off is negative, or len is negative,
or len is greater than cbuf.length - off |
read
public int read (char[] cbuf)
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.
Parameters | |
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cbuf |
char : Destination buffer |
Returns | |
---|---|
int |
The number of characters read, or -1 if the end of the stream has been reached |
Throws | |
---|---|
IOException |
If an I/O error occurs |
read
public int read (CharBuffer target)
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.
Parameters | |
---|---|
target |
CharBuffer : the buffer to read characters into |
Returns | |
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int |
The number of characters added to the buffer, or -1 if this source of characters is at its end |
Throws | |
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IOException |
if an I/O error occurs |
NullPointerException |
if target is null |
ReadOnlyBufferException |
if target is a read only buffer |
ready
public boolean ready ()
Tells whether this stream is ready to be read.
Returns | |
---|---|
boolean |
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. |
Throws | |
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IOException |
If an I/O error occurs |
reset
public void reset ()
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 | |
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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 |
skip
public long skip (long n)
Skips characters. This method will block until some characters are available, an I/O error occurs, or the end of the stream is reached.
Parameters | |
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n |
long : The number of characters to skip |
Returns | |
---|---|
long |
The number of characters actually skipped |
Throws | |
---|---|
IllegalArgumentException |
If n is negative. |
IOException |
If an I/O error occurs |
transferTo
public long transferTo (Writer out)
Reads all characters from this reader and writes the characters to the given writer in the order that they are read. On return, this reader will be at end of the stream. This method does not close either reader or writer.
This method may block indefinitely reading from the reader, or writing to the writer. The behavior for the case where the reader and/or writer is asynchronously closed, or the thread interrupted during the transfer, is highly reader and writer specific, and therefore not specified.
If an I/O error occurs reading from the reader or writing to the writer, then it may do so after some characters have been read or written. Consequently the reader may not be at end of the stream and one, or both, streams may be in an inconsistent state. It is strongly recommended that both streams be promptly closed if an I/O error occurs.
Parameters | |
---|---|
out |
Writer : the writer, non-null |
Returns | |
---|---|
long |
the number of characters transferred |
Throws | |
---|---|
IOException |
if an I/O error occurs when reading or writing |
NullPointerException |
if out is null |