Reader

public abstract class Reader extends Object
implements Readable Closeable

Known Direct Subclasses BufferedReader, CharArrayReader, FilterReader, InputStreamReader, PipedReader, StringReader BufferedReader Reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.  CharArrayReader This class implements a character buffer that can be used as a character-input stream.  FilterReader Abstract class for reading filtered character streams.  InputStreamReader An InputStreamReader is a bridge from byte streams to character streams: It reads bytes and decodes them into characters using a specified charset.  PipedReader Piped character-input streams.  StringReader A character stream whose source is a string.

Known Indirect Subclasses FileReader, LineNumberReader, PushbackReader FileReader Convenience class for reading character files.  LineNumberReader A buffered character-input stream that keeps track of line numbers.  PushbackReader A character-stream reader that allows characters to be pushed back into the stream.

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

• BufferedReader
• LineNumberReader
• CharArrayReader
• InputStreamReader
• FileReader
• FilterReader
• PushbackReader
• PipedReader
• StringReader
• Writer

Field Summary

protected Object

lock

The object used to synchronize operations on this stream.

Protected Constructor Summary

	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 Method Summary

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.
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.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.lang.Readable

abstract int

read(CharBuffer cb) Attempts to read characters into the specified character buffer.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Fields

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

protected Reader ()

Creates a new character-stream reader whose critical sections will synchronize on the reader itself.

protected Reader (Object lock)

Creates a new character-stream reader whose critical sections will synchronize on the given object.

Parameters

lock	The Object to synchronize on.

Public Methods

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

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	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

public boolean markSupported ()

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.

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

• 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

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

cbuf	Destination buffer
off	Offset at which to start storing characters
len	Maximum number of characters to read

Returns

• The number of characters read, or -1 if the end of the stream has been reached

Throws

IOException	If an I/O error occurs

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

cbuf	Destination buffer

Returns

• The number of characters read, or -1 if the end of the stream has been reached

Throws

IOException	If an I/O error occurs

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	the buffer to read characters into

Returns

• 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
NullPointerException	if target is null
ReadOnlyBufferException	if target is a read only buffer

public boolean ready ()

Tells whether this stream is ready to be read.

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.

Throws

IOException	If an I/O error occurs

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

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 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

n	The number of characters to skip

Returns

• The number of characters actually skipped

Throws

IllegalArgumentException	If n is negative.
IOException	If an I/O error occurs