- java.lang.Object
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- java.io.Reader
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- 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
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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.
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Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods 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 newReader
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.
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Field Detail
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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 thanthis
or a synchronized method.
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Constructor Detail
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Reader
protected Reader()
Creates a new character-stream reader whose critical sections will synchronize on the reader itself.
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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.
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Method Detail
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nullReader
public static Reader nullReader()
Returns a newReader
that reads no characters. The returned stream is initially open. The stream is closed by calling theclose()
method. Subsequent calls toclose()
have no effect.While the stream is open, the
read()
,read(char[])
,read(char[], int, int)
,read(Charbuffer)
,ready()
,skip(long)
, andtransferTo()
methods all behave as if end of stream has been reached. After the stream has been closed, these methods all throwIOException
.The
markSupported()
method returnsfalse
. Themark()
andreset()
methods throw anIOException
.The
object
used to synchronize operations on the returnedReader
is not specified.- Returns:
- a
Reader
which reads no characters - Since:
- 11
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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 interfaceReadable
- 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 occursNullPointerException
- if target is nullReadOnlyBufferException
- if target is a read only buffer- Since:
- 1.5
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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
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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.- 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
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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.- Parameters:
cbuf
- Destination bufferoff
- Offset at which to start storing characterslen
- 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 occursIndexOutOfBoundsException
- Ifoff
is negative, orlen
is negative, orlen
is greater thancbuf.length - off
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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.- Parameters:
n
- The number of characters to skip- Returns:
- The number of characters actually skipped
- Throws:
IllegalArgumentException
- Ifn
is negative.IOException
- If an I/O error occurs
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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
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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.
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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
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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
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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 interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Throws:
IOException
- If an I/O error occurs
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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 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 writingNullPointerException
- ifout
isnull
- Since:
- 10
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