FileDocCategorySizeDatePackage
BufferedReader.javaAPI DocJava SE 6 API14593Tue Jun 10 00:25:32 BST 2008java.io

BufferedReader

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.

see
FileReader
see
InputStreamReader
version
1.37, 06/03/15
author
Mark Reinhold
since
JDK1.1

Fields Summary
private Reader
in
private char[]
cb
private int
nChars
private int
nextChar
private static final int
INVALIDATED
private static final int
UNMARKED
private int
markedChar
private int
readAheadLimit
private boolean
skipLF
If the next character is a line feed, skip it
private boolean
markedSkipLF
The skipLF flag when the mark was set
private static int
defaultCharBufferSize
private static int
defaultExpectedLineLength
Constructors Summary
public BufferedReader(Reader in, int sz)
Creates a buffering character-input stream that uses an input buffer of the specified size.

param
in A Reader
param
sz Input-buffer size
exception
IllegalArgumentException If sz is <= 0


                                              
         
	super(in);
	if (sz <= 0)
	    throw new IllegalArgumentException("Buffer size <= 0");
	this.in = in;
	cb = new char[sz];
	nextChar = nChars = 0;
    
public BufferedReader(Reader in)
Creates a buffering character-input stream that uses a default-sized input buffer.

param
in A Reader

	this(in, defaultCharBufferSize);
    
Methods Summary
public voidclose()

	synchronized (lock) {
	    if (in == null)
		return;
	    in.close();
	    in = null;
	    cb = null;
	}
    
private voidensureOpen()
Checks to make sure that the stream has not been closed

	if (in == null)
	    throw new IOException("Stream closed");
    
private voidfill()
Fills the input buffer, taking the mark into account if it is valid.

	int dst;
	if (markedChar <= UNMARKED) {
	    /* No mark */
	    dst = 0;
	} else {
	    /* Marked */
	    int delta = nextChar - markedChar;
	    if (delta >= readAheadLimit) {
		/* Gone past read-ahead limit: Invalidate mark */
		markedChar = INVALIDATED;
		readAheadLimit = 0;
		dst = 0;
	    } else {
		if (readAheadLimit <= cb.length) {
		    /* Shuffle in the current buffer */
		    System.arraycopy(cb, markedChar, cb, 0, delta);
		    markedChar = 0;
		    dst = delta;
		} else {
		    /* Reallocate buffer to accommodate read-ahead limit */
		    char ncb[] = new char[readAheadLimit];
		    System.arraycopy(cb, markedChar, ncb, 0, delta);
		    cb = ncb;
		    markedChar = 0;
		    dst = delta;
		}
                nextChar = nChars = delta;
	    }
	}

	int n;
	do {
	    n = in.read(cb, dst, cb.length - dst);
	} while (n == 0);
	if (n > 0) {
	    nChars = dst + n;
	    nextChar = dst;
	}
    
public voidmark(int readAheadLimit)
Marks the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point.

param
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.
exception
IllegalArgumentException If readAheadLimit is < 0
exception
IOException If an I/O error occurs

	if (readAheadLimit < 0) {
	    throw new IllegalArgumentException("Read-ahead limit < 0");
	}
	synchronized (lock) {
	    ensureOpen();
	    this.readAheadLimit = readAheadLimit;
	    markedChar = nextChar;
	    markedSkipLF = skipLF;
	}
    
public booleanmarkSupported()
Tells whether this stream supports the mark() operation, which it does.

	return true;
    
public intread()
Reads a single character.

return
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
exception
IOException If an I/O error occurs

	synchronized (lock) {
	    ensureOpen();
	    for (;;) {
		if (nextChar >= nChars) {
		    fill();
		    if (nextChar >= nChars)
			return -1;
		}
		if (skipLF) {
		    skipLF = false;
		    if (cb[nextChar] == '\n") {
			nextChar++;
			continue;
		    }
		}
		return cb[nextChar++];
	    }
	}
    
public intread(char[] cbuf, int off, int len)
Reads characters into a portion of an array.

This method implements the general contract of the corresponding {@link Reader#read(char[], int, int) read} method of the {@link 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.

param
cbuf Destination buffer
param
off Offset at which to start storing characters
param
len Maximum number of characters to read
return
The number of characters read, or -1 if the end of the stream has been reached
exception
IOException If an I/O error occurs

        synchronized (lock) {
	    ensureOpen();
            if ((off < 0) || (off > cbuf.length) || (len < 0) ||
                ((off + len) > cbuf.length) || ((off + len) < 0)) {
                throw new IndexOutOfBoundsException();
            } else if (len == 0) {
                return 0;
            }

	    int n = read1(cbuf, off, len);
	    if (n <= 0) return n;
	    while ((n < len) && in.ready()) {
		int n1 = read1(cbuf, off + n, len - n);
		if (n1 <= 0) break;
		n += n1;
	    }
	    return n;
	}
    
private intread1(char[] cbuf, int off, int len)
Reads characters into a portion of an array, reading from the underlying stream if necessary.

	if (nextChar >= nChars) {
	    /* If the requested length is at least as large as the buffer, and
	       if there is no mark/reset activity, and if line feeds are not
	       being skipped, do not bother to copy the characters into the
	       local buffer.  In this way buffered streams will cascade
	       harmlessly. */
	    if (len >= cb.length && markedChar <= UNMARKED && !skipLF) {
		return in.read(cbuf, off, len);
	    }
	    fill();
	}
	if (nextChar >= nChars) return -1;
	if (skipLF) {
	    skipLF = false;
	    if (cb[nextChar] == '\n") {
		nextChar++;
		if (nextChar >= nChars)
		    fill();
		if (nextChar >= nChars)
		    return -1;
	    }
	}
	int n = Math.min(len, nChars - nextChar);
	System.arraycopy(cb, nextChar, cbuf, off, n);
	nextChar += n;
	return n;
    
java.lang.StringreadLine(boolean ignoreLF)
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.

param
ignoreLF If true, the next '\n' will be skipped
return
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
see
java.io.LineNumberReader#readLine()
exception
IOException If an I/O error occurs

	StringBuffer s = null;
	int startChar;

        synchronized (lock) {
            ensureOpen();
	    boolean omitLF = ignoreLF || skipLF;

	bufferLoop:
	    for (;;) {

		if (nextChar >= nChars)
		    fill();
		if (nextChar >= nChars) { /* EOF */
		    if (s != null && s.length() > 0)
			return s.toString();
		    else
			return null;
		}
		boolean eol = false;
		char c = 0;
		int i;

                /* Skip a leftover '\n', if necessary */
		if (omitLF && (cb[nextChar] == '\n")) 
                    nextChar++;
		skipLF = false;
		omitLF = false;

	    charLoop:
		for (i = nextChar; i < nChars; i++) {
		    c = cb[i];
		    if ((c == '\n") || (c == '\r")) {
			eol = true;
			break charLoop;
		    }
		}

		startChar = nextChar;
		nextChar = i;

		if (eol) {
		    String str;
		    if (s == null) {
			str = new String(cb, startChar, i - startChar);
		    } else {
			s.append(cb, startChar, i - startChar);
			str = s.toString();
		    }
		    nextChar++;
		    if (c == '\r") {
			skipLF = true;
		    }
		    return str;
		}
		
		if (s == null) 
		    s = new StringBuffer(defaultExpectedLineLength);
		s.append(cb, startChar, i - startChar);
	    }
        }
    
public java.lang.StringreadLine()
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.

return
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
exception
IOException If an I/O error occurs

        return readLine(false);
    
public booleanready()
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.

exception
IOException If an I/O error occurs

	synchronized (lock) {
	    ensureOpen();

	    /* 
	     * If newline needs to be skipped and the next char to be read
	     * is a newline character, then just skip it right away.
	     */
	    if (skipLF) {
		/* Note that in.ready() will return true if and only if the next 
		 * read on the stream will not block.
		 */
		if (nextChar >= nChars && in.ready()) {
		    fill();
		}
		if (nextChar < nChars) {
		    if (cb[nextChar] == '\n") 
			nextChar++;
		    skipLF = false;
		} 
	    }
	    return (nextChar < nChars) || in.ready();
	}
    
public voidreset()
Resets the stream to the most recent mark.

exception
IOException If the stream has never been marked, or if the mark has been invalidated

	synchronized (lock) {
	    ensureOpen();
	    if (markedChar < 0)
		throw new IOException((markedChar == INVALIDATED)
				      ? "Mark invalid"
				      : "Stream not marked");
	    nextChar = markedChar;
	    skipLF = markedSkipLF;
	}
    
public longskip(long n)
Skips characters.

param
n The number of characters to skip
return
The number of characters actually skipped
exception
IllegalArgumentException If n is negative.
exception
IOException If an I/O error occurs

	if (n < 0L) {
	    throw new IllegalArgumentException("skip value is negative");
	}
	synchronized (lock) {
	    ensureOpen();
	    long r = n;
	    while (r > 0) {
		if (nextChar >= nChars)
		    fill();
		if (nextChar >= nChars)	/* EOF */
		    break;
		if (skipLF) {
		    skipLF = false;
		    if (cb[nextChar] == '\n") {
			nextChar++;
		    }
		}
		long d = nChars - nextChar;
		if (r <= d) {
		    nextChar += r;
		    r = 0;
		    break;
		}
		else {
		    r -= d;
		    nextChar = nChars;
		}
	    }
	    return n - r;
	}