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BufferedWriter (Java Platform SE 6) - JDK 5 Documentation v6.0, Java 2 SDK 英文文档


Java™ Platform
Standard Ed. 6

java.io
Class BufferedWriter

java.lang.Object
  extended by java.io.Writer
      extended by java.io.BufferedWriter
All Implemented Interfaces:
Closeable, Flushable, Appendable

public class BufferedWriter
extends Writer

Writes text to a character-output stream, buffering characters so as to provide for the efficient writing of single characters, arrays, and strings.

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

A newLine() method is provided, which uses the platform's own notion of line separator as defined by the system property line.separator. Not all platforms use the newline character ('\n') to terminate lines. Calling this method to terminate each output line is therefore preferred to writing a newline character directly.

In general, a Writer sends its output immediately to the underlying character or byte stream. Unless prompt output is required, it is advisable to wrap a BufferedWriter around any Writer whose write() operations may be costly, such as FileWriters and OutputStreamWriters. For example,

 PrintWriter out
   = new PrintWriter(new BufferedWriter(new FileWriter("foo.out")));
 
will buffer the PrintWriter's output to the file. Without buffering, each invocation of a print() method would cause characters to be converted into bytes that would then be written immediately to the file, which can be very inefficient.

Since:
JDK1.1
See Also:
PrintWriter, FileWriter, OutputStreamWriter

Field Summary
 
Fields inherited from class java.io.Writer
lock
 
Constructor Summary
BufferedWriter(Writer out)
          Creates a buffered character-output stream that uses a default-sized output buffer.
BufferedWriter(Writer out, int sz)
          Creates a new buffered character-output stream that uses an output buffer of the given size.
 
Method Summary
 void close()
          Closes the stream, flushing it first.
 void flush()
          Flushes the stream.
 void newLine()
          Writes a line separator.
 void write(char[] cbuf, int off, int len)
          Writes a portion of an array of characters.
 void write(int c)
          Writes a single character.
 void write(String s, int off, int len)
          Writes a portion of a String.
 
Methods inherited from class java.io.Writer
append, append, append, write, write
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

BufferedWriter

public BufferedWriter(Writer out)
Creates a buffered character-output stream that uses a default-sized output buffer.

Parameters:
out - A Writer

BufferedWriter

public BufferedWriter(Writer out,
                      int sz)
Creates a new buffered character-output stream that uses an output buffer of the given size.

Parameters:
out - A Writer
sz - Output-buffer size, a positive integer
Throws:
IllegalArgumentException - If sz is <= 0
Method Detail

write

public void write(int c)
           throws IOException
Writes a single character.

Overrides:
write in class Writer
Parameters:
c - int specifying a character to be written
Throws:
IOException - If an I/O error occurs

write

public void write(char[] cbuf,
                  int off,
                  int len)
           throws IOException
Writes a portion of an array of characters.

Ordinarily this method stores characters from the given array into this stream's buffer, flushing the buffer to the underlying stream as needed. If the requested length is at least as large as the buffer, however, then this method will flush the buffer and write the characters directly to the underlying stream. Thus redundant BufferedWriters will not copy data unnecessarily.

Specified by:
write in class Writer
Parameters:
cbuf - A character array
off - Offset from which to start reading characters
len - Number of characters to write
Throws:
IOException - If an I/O error occurs

write

public void write(String s,
                  int off,
                  int len)
           throws IOException
Writes a portion of a String.

If the value of the len parameter is negative then no characters are written. This is contrary to the specification of this method in the superclass, which requires that an IndexOutOfBoundsException be thrown.

Overrides:
write in class Writer
Parameters:
s - String to be written
off - Offset from which to start reading characters
len - Number of characters to be written
Throws:
IOException - If an I/O error occurs

newLine

public void newLine()
             throws IOException
Writes a line separator. The line separator string is defined by the system property line.separator, and is not necessarily a single newline ('\n') character.

Throws:
IOException - If an I/O error occurs

flush

public void flush()
           throws IOException
Flushes the stream.

Specified by:
flush in interface Flushable
Specified by:
flush in class Writer
Throws:
IOException - If an I/O error occurs

close

public void close()
           throws IOException
Description copied from class: Writer
Closes the stream, flushing it first. Once the stream has been closed, further write() or flush() invocations will cause an IOException to be thrown. Closing a previously closed stream has no effect.

Specified by:
close in interface Closeable
Specified by:
close in class Writer
Throws:
IOException - If an I/O error occurs

Java™ Platform
Standard Ed. 6

Submit a bug or feature
For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2006 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.