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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class BufferedReader - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.io
Class BufferedReader

java.lang.Object
  |
  +--java.io.Reader
        |
        +--java.io.BufferedReader
Direct Known Subclasses:
LineNumberReader
public class BufferedReader
extends Reader

Read text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.

The buffer size may be specified, or the default size may be used. The default is large enough for most purposes.

In general, each read request made of a Reader causes a corresponding read request to be made of the underlying character or byte stream. It is therefore advisable to wrap a BufferedReader around any Reader whose read() operations may be costly, such as FileReaders and InputStreamReaders. For example, 

 BufferedReader in
   = new BufferedReader(new FileReader("foo.in"));
will buffer the input from the specified file. Without buffering, each invocation of read() or readLine() could cause bytes to be read from the file, converted into characters, and then returned, which can be very inefficient.

Programs that use DataInputStreams for textual input can be localized by replacing each DataInputStream with an appropriate BufferedReader.

Since:
JDK1.1
See Also:
FileReader, InputStreamReader

Fields inherited from class java.io.Reader
lock
 
Constructor Summary
BufferedReader(Reader in)
          Create a buffering character-input stream that uses a default-sized input buffer.
BufferedReader(Reader in, int sz)
          Create a buffering character-input stream that uses an input buffer of the specified size.
 
Method Summary
 void close()
          Close the stream.
 void mark(int readAheadLimit)
          Mark the present position in the stream.
 boolean markSupported()
          Tell whether this stream supports the mark() operation, which it does.
 int read()
          Read a single character.
 int read(char[] cbuf, int off, int len)
          Read characters into a portion of an array.
 String readLine()
          Read a line of text.
 boolean ready()
          Tell whether this stream is ready to be read.
 void reset()
          Reset the stream to the most recent mark.
 long skip(long n)
          Skip characters.
 
Methods inherited from class java.io.Reader
read
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

BufferedReader

public BufferedReader(Reader in,
                      int sz)
Create a buffering character-input stream that uses an input buffer of the specified size.
Parameters:
in - A Reader
sz - Input-buffer size
Throws:
IllegalArgumentException - If sz is <= 0

BufferedReader

public BufferedReader(Reader in)
Create a buffering character-input stream that uses a default-sized input buffer.
Parameters:
in - A Reader
Method Detail

read

public int read()
         throws IOException
Read a single character.
Overrides:
read in class Reader
Throws:
IOException - If an I/O error occurs

read

public int read(char[] cbuf,
                int off,
                int len)
         throws IOException
Read characters into a portion of an array.

This method implements the general contract of the corresponding read method of the Reader class. As an additional convenience, it attempts to read as many characters as possible by repeatedly invoking the read method of the underlying stream. This iterated read continues until one of the following conditions becomes true:

  • The specified number of characters have been read,
  • The read method of the underlying stream returns -1, indicating end-of-file, or
  • The ready method of the underlying stream returns false, indicating that further input requests would block.
If the first read on the underlying stream returns -1 to indicate end-of-file then this method returns -1. Otherwise this method returns the number of characters actually read.

Subclasses of this class are encouraged, but not required, to attempt to read as many characters as possible in the same fashion.

Ordinarily this method takes characters from this stream's character buffer, filling it from the underlying stream as necessary. If, however, the buffer is empty, the mark is not valid, and the requested length is at least as large as the buffer, then this method will read characters directly from the underlying stream into the given array. Thus redundant BufferedReaders will not copy data unnecessarily.

Overrides:
read in class Reader
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

readLine

public String readLine()
                throws IOException
Read a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.
Returns:
A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached
Throws:
IOException - If an I/O error occurs

skip

public long skip(long n)
          throws IOException
Skip characters.
Overrides:
skip in class Reader
Parameters:
n - The number of characters to skip
Returns:
The number of characters actually skipped
Throws:
IOException - If an I/O error occurs

ready

public boolean ready()
              throws IOException
Tell whether this stream is ready to be read. A buffered character stream is ready if the buffer is not empty, or if the underlying character stream is ready.
Overrides:
ready in class Reader
Throws:
IOException - If an I/O error occurs

markSupported

public boolean markSupported()
Tell whether this stream supports the mark() operation, which it does.
Overrides:
markSupported in class Reader

mark

public void mark(int readAheadLimit)
          throws IOException
Mark the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point.
Overrides:
mark in class Reader
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. A limit value larger than the size of the input buffer will cause a new buffer to be allocated whose size is no smaller than limit. Therefore large values should be used with care.
Throws:
IllegalArgumentException - If readAheadLimit is < 0
IOException - If an I/O error occurs

reset

public void reset()
           throws IOException
Reset the stream to the most recent mark.
Overrides:
reset in class Reader
Throws:
IOException - If the stream has never been marked, or if the mark has been invalidated

close

public void close()
           throws IOException
Close the stream.
Overrides:
close in class Reader
Throws:
IOException - If an I/O error occurs
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