Module java.base

Package java.io

Class Reader

java.lang.Object

java.io.Reader

All Implemented Interfaces:

Closeable, AutoCloseable, 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:

1.1

See Also:

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

Field Summary

Fields

Modifier and Type	Field	Description
protected Object	lock	The object used to synchronize operations on this stream.

Constructor Summary

Constructors

Modifier	Constructor	Description
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.

Method Summary

Modifier and Type	Method	Description
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 Reader that reads no characters.
int	read()	Reads a single character.
int	read(char[] cbuf)	Reads characters into an array.
abstract int	read(char[] cbuf, int off, int len)	Reads characters into a portion of 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.

Methods declared in class java.lang.Object

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

Field Details

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 Details

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 - The Object to synchronize on.

Method Details

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:

a Reader which reads no characters

Since:

11

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. If the length of the specified character buffer is zero, then no characters will be read and zero will be returned.

Specified by:

read in interface Readable

Parameters:

target - the buffer to read characters into

Returns:

The number of characters added to the buffer, possibly zero, 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, even if its length is zero

Since:

1.5

read

public int read()
         throws IOException

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

read

public int read(char[] cbuf)
         throws IOException

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.

If the length of cbuf is zero, then no characters are read and 0 is returned; otherwise, there is an attempt to read at least one character. If no character is available because the stream is at its end, the value -1 is returned; otherwise, at least one character is read and stored into cbuf.

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

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.

If len is zero, then no characters are read and 0 is returned; otherwise, there is an attempt to read at least one character. If no character is available because the stream is at its end, the value -1 is returned; otherwise, at least one character is read and stored into cbuf.

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:

IndexOutOfBoundsException - If off is negative, or len is negative, or len is greater than cbuf.length - off

IOException - If an I/O error occurs

skip

public long skip(long n)
          throws IOException

Skips characters. This method will block until some characters are available, an I/O error occurs, or the end of the stream is reached. If the stream is already at its end before this method is invoked, then no characters are skipped and zero is returned.

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

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

markSupported

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.

mark

public void mark(int readAheadLimit)
          throws IOException

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

reset

public void reset()
           throws IOException

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

close

public abstract void close()
                    throws IOException

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.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException - If an I/O error occurs

transferTo

public long transferTo(Writer out)
                throws IOException

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 the total number of characters transferred is greater than Long.MAX_VALUE, then Long.MAX_VALUE will be returned.

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 - the writer, non-null

Returns:

the number of characters transferred

Throws:

IOException - if an I/O error occurs when reading or writing

NullPointerException - if out is null

Since:

10