java.io
Class Reader

java.lang.Object
  java.io.Reader

Direct Known Subclasses:

BufferedReader, InputStreamReader

public abstract class Reader
extends Object

This abstract class forms the base of the hierarchy of classes that read input as a stream of characters. It provides a common set of methods for reading characters from streams. Subclasses implement and extend these methods to read characters from a particular input source such as a file or network connection.

Field Summary

protected Object

lock This is the Object used for synchronizing critical code sections.

Constructor Summary

protected	Reader() Unitializes a Reader that will use the object itself for synchronization of critical code sections.
protected	Reader(Object lock) Initializes a Reader that will use the specified Object for synchronization of critical code sections.

Method Summary

abstract void	close() Closes the stream.
void	mark(int readLimit) Marks a position in the input to which the stream can be "reset" by calling the reset() method.
boolean	markSupported() Returns a boolean that indicates whether the mark/reset methods are supported in this class.
int	read() Reads an char from the input stream and returns it as an int in the range of 0-65535.
int	read(char[] buf) Reads chars from a stream and stores them into a caller supplied buffer.
abstract int	read(char[] buf, int offset, int count) Read chars from a stream and stores them into a caller supplied buffer.
boolean	ready() Determines whether or not this stream is ready to be read.
void	reset() Resets a stream to the point where the mark() method was called.
long	skip(long count) Skips the specified number of chars in the stream.

Methods inherited from class java.lang.Object

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

Field Detail

lock

protected Object lock

This is the Object used for synchronizing critical code sections. Subclasses should use this variable instead of a synchronized method or an explicit synchronization on this

Constructor Detail

Reader

protected Reader()

Unitializes a Reader that will use the object itself for synchronization of critical code sections.

Reader

protected Reader(Object lock)

Initializes a Reader that will use the specified Object for synchronization of critical code sections.

Parameters:

lock - The Object to use for synchronization

Method Detail

read

public abstract int read(char[] buf,
                         int offset,
                         int count)
                  throws IOException

Read chars from a stream and stores them into a caller supplied buffer. It starts storing the data at index offset into the buffer and attempts to read len chars. This method can return before reading the number of chars requested. The actual number of chars read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

This method operates by calling the single char read() method in a loop until the desired number of chars are read. The read loop stops short if the end of the stream is encountered or if an IOException is encountered on any read operation except the first. If the first attempt to read a chars fails, the IOException is allowed to propagate upward. And subsequent IOException is caught and treated identically to an end of stream condition. Subclasses can (and should if possible) override this method to provide a more efficient implementation.

Parameters:

buf - The array into which the chars read should be stored

offset - The offset into the array to start storing chars

count - The requested number of chars to read

Returns:

The actual number of chars read, or -1 if end of stream.

Throws:

IOException - If an error occurs.

read

public int read(char[] buf)
         throws IOException

Reads chars from a stream and stores them into a caller supplied buffer. This method attempts to completely fill the buffer, but can return before doing so. The actual number of chars read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

This method operates by calling an overloaded read method like so: read(buf, 0, buf.length)

Parameters:

buf - The buffer into which the chars read will be stored.

Returns:

The number of chars read or -1 if end of stream.

Throws:

IOException - If an error occurs.

read

public int read()
         throws IOException

Reads an char from the input stream and returns it as an int in the range of 0-65535. This method also will return -1 if the end of the stream has been reached.

This method will block until the char can be read.

Returns:

The char read or -1 if end of stream

Throws:

IOException - If an error occurs

close

public abstract void close()
                    throws IOException

Closes the stream. Any futher attempts to read from the stream may generate an IOException.

Throws:

IOException - If an error occurs

markSupported

public boolean markSupported()

Returns a boolean that indicates whether the mark/reset methods are supported in this class. Those methods can be used to remember a specific point in the stream and reset the stream to that point.

This method always returns false in this class, but subclasses can override this method to return true if they support mark/reset functionality.

Returns:

true if mark/reset functionality is supported, false otherwise

mark

public void mark(int readLimit)
          throws IOException

Marks a position in the input to which the stream can be "reset" by calling the reset() method. The parameter readlimit is the number of chars that can be read from the stream after setting the mark before the mark becomes invalid. For example, if mark() is called with a read limit of 10, then when 11 chars of data are read from the stream before the reset() method is called, then the mark is invalid and the stream object instance is not required to remember the mark.

Parameters:

readLimit - The number of chars that can be read before the mark becomes invalid

Throws:

IOException - If an error occurs such as mark not being supported for this class

reset

public void reset()
           throws IOException

Resets a stream to the point where the mark() method was called. Any chars that were read after the mark point was set will be re-read during subsequent reads.

This method always throws an IOException in this class, but subclasses can override this method if they provide mark/reset functionality.

Throws:

IOException - Always thrown for this class

ready

public boolean ready()
              throws IOException

Determines whether or not this stream is ready to be read. If it returns false the stream may block if a read is attempted, but it is not guaranteed to do so.

This method always returns false in this class

Returns:

true if the stream is ready to be read, false otherwise.

Throws:

IOException - If an error occurs

skip

public long skip(long count)
          throws IOException

Skips the specified number of chars in the stream. It returns the actual number of chars skipped, which may be less than the requested amount.

This method reads and discards chars into a 256 char array until the specified number of chars were skipped or until either the end of stream is reached or a read attempt returns a short count. Subclasses can override this method to provide a more efficient implementation where one exists.

Parameters:

count - The requested number of chars to skip

Returns:

The actual number of chars skipped.

Throws:

IOException - If an error occurs