java.io
Class Reader

java.lang.Object   
  java.io.Reader

All Implemented Interfaces:

Closeable , Readable

Direct Known Subclasses:

BufferedReader , CharArrayReader , FilterReader , InputStreamReader , PipedReader , StringReader

public abstract class Reader
extends Object   
implements Readable   , Closeable   

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.

Since:

JDK1.1

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.

Constructor Summary

protected	Reader () Create a new character-stream reader whose critical sections will synchronize on the reader itself.
protected	Reader (Object lock) Create a new character-stream reader whose critical sections will synchronize on the given object.

Method Summary

abstract void	close () Close the stream.
void	mark (int readAheadLimit) Mark the present position in the stream.
boolean	markSupported () Tell whether this stream supports the mark() operation.
int	read () Read a single character.
int	read (char[] cbuf) Read characters into an array.
abstract int	read (char[] cbuf, int off, int len) Read characters into a portion of an array.
int	read (CharBuffer target) Attempts to read characters into the specified character buffer.
boolean	ready () Tell whether this stream is ready to be read.
void	reset () Reset the stream.
long	skip (long n) Skip characters.

Methods inherited from class java.lang.Object

clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait

Field Detail

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.

Constructor Detail

Reader

protected Reader()

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

Reader

protected Reader(Object    lock)

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

Parameters:

lock - The Object to synchronize on.

Method Detail

read

public int read(CharBuffer    target)
         throws IOException   

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.

Specified by:

read in interface Readable

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

read

public int read()
         throws IOException   

Read 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

read

public int read(char[] cbuf)
         throws IOException   

Read 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

read

public abstract int read(char[] cbuf,
                         int off,
                         int len)
                  throws IOException   

Read 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

skip

public long skip(long n)
          throws IOException   

Skip 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

ready

public boolean ready()
              throws IOException   

Tell 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

markSupported

public boolean markSupported()

Tell 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.

mark

public void mark(int readAheadLimit)
          throws IOException   

Mark 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

reset

public void reset()
           throws IOException   

Reset 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

close

public abstract void close()
                    throws IOException   

Close the stream. Once a stream has been closed, further read(), ready(), mark(), or reset() invocations will throw an IOException. Closing a previously-closed stream, however, has no effect.

Specified by:

close in interface Closeable

Throws:

IOException - If an I/O error occurs