Java™ Platform
Standard Ed. 6

java.io
Class BufferedReader

java.lang.Object
  extended by java.io.Reader
      extended by java.io.BufferedReader
All Implemented Interfaces:
Closeable, Readable
Direct Known Subclasses:
LineNumberReader

public class BufferedReader
extends Reader

Reads 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

Field Summary
 
Fields inherited from class java.io.Reader
lock
 
Constructor Summary
BufferedReader(Reader in)
          Creates a buffering character-input stream that uses a default-sized input buffer.
BufferedReader(Reader in, int sz)
          Creates a buffering character-input stream that uses an input buffer of the specified size.
 
Method Summary
 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, which it does.
 int read()
          Reads a single character.
 int read(char[] cbuf, int off, int len)
          Reads characters into a portion of an array.
 String readLine()
          Reads a line of text.
 boolean ready()
          Tells whether this stream is ready to be read.
 void reset()
          Resets the stream to the most recent mark.
 long skip(long n)
          Skips characters.
 
Methods inherited from class java.io.Reader
read, 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)
Creates 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)
Creates a buffering character-input stream that uses a default-sized input buffer.

Parameters:
in - A Reader
Method Detail

read

public int read()
         throws IOException
Reads a single character.

Overrides:
read in class Reader
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,
                int off,
                int len)
         throws IOException
Reads 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:

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.

Specified by:
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
Reads 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
Skips characters.

Overrides:
skip in class Reader
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. 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
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, which it does.

Overrides:
markSupported in class Reader
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.

Overrides:
mark in class Reader
Parameters:
readAheadLimit - Limit on the number of characters that may be read while still preserving the mark. An attempt to reset the stream after reading characters up to this limit or beyond 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
Resets 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
Description copied from class: Reader
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 Closeable
Specified by:
close in class Reader
Throws:
IOException - If an I/O error occurs

Java™ Platform
Standard Ed. 6

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