Reader

public abstract class Reader extends Object
implements Readable Closeable
Known Direct Subclasses
Known Indirect Subclasses

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.

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

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
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