java.io
public class: BufferedReader [javadoc |
source]
java.lang.Object
java.io.Reader
java.io.BufferedReader
All Implemented Interfaces:
Closeable, Readable
Direct Known Subclasses:
LineNumberReader
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.
| Constructor: |
|---|
 public BufferedReader(Reader in) {
this(in, defaultCharBufferSize);
}
Creates a buffering character-input stream that uses a default-sized
input buffer. |
public BufferedReader(Reader in,
int sz) {
super(in);
if (sz < = 0)
throw new IllegalArgumentException("Buffer size < = 0");
this.in = in;
cb = new char[sz];
nextChar = nChars = 0;
} Creates a buffering character-input stream that uses an input buffer of
the specified size. Parameters:
in - A Reader
sz - Input-buffer size
IllegalArgumentException - If sz is <= 0
- exception:
IllegalArgumentException - If sz is <= 0
|
| Methods from java.lang.Object: |
|---|
|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Method from java.io.BufferedReader Detail: |
|---|
public void close() throws IOException {
synchronized (lock) {
if (in == null)
return;
in.close();
in = null;
cb = null;
}
} |
public void mark(int readAheadLimit) throws IOException {
if (readAheadLimit < 0) {
throw new IllegalArgumentException("Read-ahead limit < 0");
}
synchronized (lock) {
ensureOpen();
this.readAheadLimit = readAheadLimit;
markedChar = nextChar;
markedSkipLF = skipLF;
}
} Marks the present position in the stream. Subsequent calls to reset()
will attempt to reposition the stream to this point. |
public boolean markSupported() {
return true;
} Tells whether this stream supports the mark() operation, which it does. |
public int read() throws IOException {
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++];
}
}
} Reads a single character. |
public int read(char[] cbuf,
int off,
int len) throws IOException {
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;
}
} 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:
- 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. |
public String readLine() throws IOException {
return readLine(false);
} 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. |
String readLine(boolean ignoreLF) throws IOException {
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);
}
}
} 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. |
public boolean ready() throws IOException {
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();
}
} 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. |
public void reset() throws IOException {
synchronized (lock) {
ensureOpen();
if (markedChar < 0)
throw new IOException((markedChar == INVALIDATED)
? "Mark invalid"
: "Stream not marked");
nextChar = markedChar;
skipLF = markedSkipLF;
}
} Resets the stream to the most recent mark. |
public long skip(long n) throws IOException {
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;
}
} |