- 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,- URLReader
 
 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 SummaryConstructors Modifier Constructor Description protectedReader()Creates a new character-stream reader whose critical sections will synchronize on the reader itself.protectedReader(Object lock)Creates a new character-stream reader whose critical sections will synchronize on the given object.
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Method SummaryAll Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract voidclose()Closes the stream and releases any system resources associated with it.voidmark(int readAheadLimit)Marks the present position in the stream.booleanmarkSupported()Tells whether this stream supports the mark() operation.static ReadernullReader()Returns a newReaderthat reads no characters.intread()Reads a single character.intread(char[] cbuf)Reads characters into an array.abstract intread(char[] cbuf, int off, int len)Reads characters into a portion of an array.intread(CharBuffer target)Attempts to read characters into the specified character buffer.booleanready()Tells whether this stream is ready to be read.voidreset()Resets the stream.longskip(long n)Skips characters.longtransferTo(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- 
lockprotected 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 thanthisor a synchronized method.
 
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Constructor Detail- 
Readerprotected Reader() Creates a new character-stream reader whose critical sections will synchronize on the reader itself.
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Readerprotected 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- 
nullReaderpublic static Reader nullReader() Returns a newReaderthat 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 objectused to synchronize operations on the returnedReaderis not specified.- Returns:
- a Readerwhich reads no characters
- Since:
- 11
 
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readpublic 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:
- readin 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
- Since:
- 1.5
 
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readpublic int read() throws IOExceptionReads 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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readpublic int read(char[] cbuf) throws IOExceptionReads 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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readpublic abstract int read(char[] cbuf, int off, int len) throws IOExceptionReads 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
- IndexOutOfBoundsException- If- offis negative, or- lenis negative, or- lenis greater than- cbuf.length - off
 
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skippublic long skip(long n) throws IOExceptionSkips 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- nis negative.
- IOException- If an I/O error occurs
 
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readypublic boolean ready() throws IOExceptionTells 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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markSupportedpublic 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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markpublic void mark(int readAheadLimit) throws IOExceptionMarks 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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resetpublic void reset() throws IOExceptionResets 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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closepublic abstract void close() throws IOExceptionCloses 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:
- closein interface- AutoCloseable
- Specified by:
- closein interface- Closeable
- Throws:
- IOException- If an I/O error occurs
 
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transferTopublic 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 writing
- NullPointerException- if- outis- null
- Since:
- 10
 
 
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